I am afraid you can&#39;t. Why not write dependency modules in Kotlin?

To write dependency modules in java, you need to configure your Gradle script in this way:

&gt;      compile &#39;com.google.dagger:dagger:2.8&#39;
&gt;      apt &#39;com.google.dagger:dagger-compiler:2.8&#39;

But, to write dependency modules in Kotlin, you should configure your Gradle script  in this way:

&gt;     compile &#39;com.google.dagger:dagger:2.8&#39; 
&gt;     kapt &#39;com.google.dagger:dagger-compiler:2.8&#39;

dagger need the annotation processing tool to generate the dependency code during the compiling process. So I guess you just need to use the right APT(annotation processing tool) according to right language.

I created a service SocketService, basically it initializes the socket to let the app listen on the port. This service also interacts with some components.

**// socket.service.ts**

    export class SocketService {
        constructor() {
            // Initializes the socket
        }
        ...
    }

I know the code in SocketService&#39;s constructor() only starts to run when a component use SocketService.

And usually the code in app.ts looks like this:

**// app.ts**

    import {SocketService} from &#39;./socket.service&#39;;
    ...
    class App {
        constructor () {}
    }
    bootstrap(App, [SocketService]);

However, I want this service run when the app starts. So I made a trick, just add `private _socketService: SocketService` in App&#39;s constructor(). So now the codes look like this:

**// app.ts (new)**

    import {SocketService} from &#39;./socket.service&#39;;
    ...
    class App {
        constructor (private _socketService: SocketService) {}
    }
    bootstrap(App, [SocketService]);

Now it works. The problem is sometimes the codes in SocketService&#39;s constructor() run, sometimes not. So how should I do it correctly? Thanks

How to run a service when the app starts in Angular 2

I&#39;m trying to run this command in Laravel 5.2 but it&#39;s not working:

    php artisan make:auth 

And prompts with these statements:


    [InvalidArgumentException]
      Command &quot;make:auth&quot; is not defined
      Did you mean one of these?  
    
    
          make:test
          make:request
          make:migration
          make:seeder
          make:middleware
          make:controller
          make:provider
          make:policy
          make:event
          make:console
          make:job
          make:listener
          make:model
          make:command

Php artisan make:auth command is not defined

I&#39;m getting this note in the build whenever I do an inject into a kotlin class (btw, I have a mixed android project with both kotlin and java).

For example, after this gradle task: `compileStagingDebugJavaWithJavac` (StagingDebug is my build variant), I get this message:

&gt; &quot;Note: Generating a MembersInjector or Factory for com.packageNameXXX.CourseDiscoveryMapFragment. Prefer to run the dagger processor over that class instead.&quot;

My **CourseDiscoveryMapFragment** code can be seen here:

    class CourseDiscoveryMapFragment : Fragment(){
    
        @Inject
        lateinit var presenter: CourseDiscoveryMapPresenter
    
        lateinit var mapView: MapView
    
        override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?, savedInstanceState: Bundle?): View? {
    
            val view = inflater.inflate(R.layout.fragment_discovery_map, container, false)
    
            MapsInitializer.initialize(activity)
    
            mapView = view.mapView
            mapView.onCreate(savedInstanceState?.getBundle(BUNDLE_KEY_MAP_STATE))
    
            (activity as BaseActivity)
                    .activityComponent.inject(this)
    }

And my **ActivityComponent** is :

    @ActivityScope
    @Subcomponent(modules = ActivityModule.class)
    public interface ActivityComponent {
    
        void inject(BaseActivity baseActivity);
    
        void inject(CourseDiscoveryMapFragment fragment);
    
        //Exposed to sub-graphs.
        Activity activity();
    }

So, I&#39;m having dagger component and modules written in Java, while having dagger injections in Kotlin.

Is this anything that I should be worried about?

Thank you. 

&quot;Prefer to run the dagger processor over that class instead&quot; in Kotlin

I'm getting this note in the build whenever I do an inject into a kotlin class (btw, I have a mixed android project with both kotlin and java).
For example, after this gradle task: <code>compileStagingDebugJavaWithJavac</code> (StagingDebug is my build variant), I get this message:
> "Note: Generating a MembersInjector or Factory for com.packageNameXXX.CourseDiscoveryMapFragment. Prefer to run the dagger processor over that class instead."
My CourseDiscoveryMapFragment code can be seen here:
<pre><code class="hljs language-kotlin">class CourseDiscoveryMapFragment : Fragment(){

 @Inject
 lateinit var presenter: CourseDiscoveryMapPresenter

 lateinit var mapView: MapView

 override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?, savedInstanceState: Bundle?): View? {

 val view = inflater.inflate(R.layout.fragment_discovery_map, container, false)

 MapsInitializer.initialize(activity)

 mapView = view.mapView
 mapView.onCreate(savedInstanceState?.getBundle(BUNDLE_KEY_MAP_STATE))

 (activity as BaseActivity)
 .activityComponent.inject(this)
}
</code></pre>
And my ActivityComponent is :
<pre><code class="hljs language-less">@ActivityScope
@Subcomponent(modules = ActivityModule.class)
public interface ActivityComponent {

 void inject(BaseActivity baseActivity);

 void inject(CourseDiscoveryMapFragment fragment);

 //Exposed to sub-graphs.
 Activity activity();
}
</code></pre>
So, I'm having dagger component and modules written in Java, while having dagger injections in Kotlin.
Is this anything that I should be worried about?
Thank you.

I am having trouble in implementing databinding in a Dialog. Is it possible?

Below is my xml.

&lt;?xml version=&quot;1.0&quot; encoding=&quot;utf-8&quot;?&gt;
&lt;layout xmlns:android=&quot;http://schemas.android.com/apk/res/android&quot;&gt;

    &lt;data&gt;

        &lt;variable
            name=&quot;olaBooking&quot;
            type=&quot;com.example.myapp.viewmodels.ViewModel&quot; /&gt;
    &lt;/data&gt;

    &lt;LinearLayout
        android:layout_width=&quot;match_parent&quot;
        android:layout_height=&quot;match_parent&quot;&gt;

        &lt;android.support.v7.widget.CardView
            android:id=&quot;@+id/cv&quot;
            android:layout_width=&quot;match_parent&quot;
            android:layout_height=&quot;wrap_content&quot;
            android:layout_margin=&quot;15dp&quot;
            android:elevation=&quot;4dp&quot;
            android:padding=&quot;15dp&quot;&gt;

            &lt;LinearLayout
                android:layout_width=&quot;match_parent&quot;
                android:layout_height=&quot;wrap_content&quot;
                android:orientation=&quot;vertical&quot;&gt;

                &lt;TextView
                    android:layout_width=&quot;match_parent&quot;
                    android:layout_height=&quot;wrap_content&quot;
                    android:background=&quot;@color/colorPrimary&quot;
                    android:gravity=&quot;center&quot;
                    android:padding=&quot;15dp&quot;
                    android:text=&quot;OLA Cab Booked !&quot;
                    android:textAppearance=&quot;@style/TextAppearance.AppCompat.Body1&quot; /&gt;

                &lt;View
                    android:layout_width=&quot;match_parent&quot;
                    android:layout_height=&quot;2dp&quot;
                    android:background=&quot;@color/colorPrimaryDark&quot; /&gt;

                &lt;TextView
                    android:layout_width=&quot;match_parent&quot;
                    android:layout_height=&quot;wrap_content&quot;
                    android:gravity=&quot;start|center&quot;
                    android:padding=&quot;15dp&quot;
                    android:text=&quot;Car Details&quot; /&gt;

                &lt;View
                    android:layout_width=&quot;match_parent&quot;
                    android:layout_height=&quot;2dp&quot;
                    android:background=&quot;@color/colorPrimaryDark&quot; /&gt;

                &lt;TextView
                    android:id=&quot;@+id/driverName&quot;
                    android:layout_width=&quot;match_parent&quot;
                    android:layout_height=&quot;wrap_content&quot;
                    android:padding=&quot;5dp&quot;
                    android:text=&quot;@{olaBooking.driverName}&quot; /&gt;

                &lt;TextView
                    android:id=&quot;@+id/carModel&quot;
                    android:layout_width=&quot;match_parent&quot;
                    android:layout_height=&quot;wrap_content&quot;
                    android:padding=&quot;5dp&quot;
                    android:text=&quot;@{olaBooking.getCarName}&quot; /&gt;

                &lt;TextView
                    android:id=&quot;@+id/carNo&quot;
                    android:layout_width=&quot;match_parent&quot;
                    android:layout_height=&quot;wrap_content&quot;
                    android:padding=&quot;5dp&quot;
                    android:text=&quot;@{olaBooking.getCabNo}&quot; /&gt;

                &lt;TextView
                    android:id=&quot;@+id/eta&quot;
                    android:layout_width=&quot;match_parent&quot;
                    android:layout_height=&quot;wrap_content&quot;
                    android:padding=&quot;5dp&quot;
                    android:text=&quot;@{olaBooking.getEta}&quot; /&gt;
            &lt;/LinearLayout&gt;
        &lt;/android.support.v7.widget.CardView&gt;
    &lt;/LinearLayout&gt;
&lt;/layout&gt;

I want to bind the above layout in a Dialog. How is it possible? Below is my java code i tried but it&#39;s not working 

            dialog.setContentView(R.layout.dialog_ola_booking_confirmed);
        DialogOlaBookingConfirmedBinding binding = DataBindingUtil.inflate(
                LayoutInflater.from(dialog.getContext()),
                R.layout.dialog_ola_booking_confirmed,
                (ViewGroup) dialog.findViewById(R.id.cv),
                false);
        ViewModel viewModel = new ViewModel(this, event.olaBooking);

How to use data-binding in Dialog?

I&#39;m currently trying to get the [ES6 react-native-webpack-server][1] running
on an Android emulator. The difference is I&#39;ve upgraded my `package.json` and `build.grade` to use react `0.18.0`, and am getting this error on boot. As far as I&#39;m aware `AppRegistry` is imported correctly. Even if I were to comment out the code this error still comes up. This does work on iOS without issue. 

What am I doing wrong?

EDIT: After trying other boilerplates that do support 0.18.0, I&#39;m still coming across the same issue.

[![enter image description here][2]][2]


  [1]: https://github.com/mjohnston/react-native-webpack-server/tree/master/Examples/BabelES6
  [2]: http://i.stack.imgur.com/HJqqQ.png

React-Native: Module AppRegistry is not a registered callable module

I want to change the text of a TextView inside the navigation drawer header. But I get this error:

&gt; java.lang.NullPointerException: Attempt to invoke virtual method &#39;void
&gt; android.widget.TextView.setText(java.lang.CharSequence)&#39; on a null
&gt; object reference

---------
**activity_main.xml**

    &lt;?xml version=&quot;1.0&quot; encoding=&quot;utf-8&quot;?&gt;
    &lt;android.support.v4.widget.DrawerLayout xmlns:android=&quot;http://schemas.android.com/apk/res/android&quot;
        xmlns:app=&quot;http://schemas.android.com/apk/res-auto&quot;
        xmlns:tools=&quot;http://schemas.android.com/tools&quot;
        android:id=&quot;@+id/drawer_layout&quot;
        android:layout_width=&quot;match_parent&quot;
        android:layout_height=&quot;match_parent&quot;
        android:fitsSystemWindows=&quot;true&quot;
        tools:openDrawer=&quot;start&quot;&gt;
    
        &lt;LinearLayout
            android:layout_width=&quot;match_parent&quot;
            android:layout_height=&quot;match_parent&quot;
            android:orientation=&quot;vertical&quot;&gt;
    
            &lt;include
                layout=&quot;@layout/app_bar_main&quot;
                android:layout_width=&quot;match_parent&quot;
                android:layout_height=&quot;wrap_content&quot; /&gt;
    
            &lt;FrameLayout
                android:id=&quot;@+id/frame_container&quot;
                android:layout_width=&quot;match_parent&quot;
                android:layout_height=&quot;match_parent&quot; /&gt;
    
        &lt;/LinearLayout&gt;
    
        &lt;android.support.design.widget.NavigationView
            android:id=&quot;@+id/nav_view&quot;
            android:layout_width=&quot;wrap_content&quot;
            android:layout_height=&quot;match_parent&quot;
            android:layout_gravity=&quot;start&quot;
            android:fitsSystemWindows=&quot;true&quot;
            app:headerLayout=&quot;@layout/nav_header_main&quot;
            app:menu=&quot;@menu/activity_main_drawer&quot; /&gt;
    
    &lt;/android.support.v4.widget.DrawerLayout&gt;

**nav_header_main**

    &lt;?xml version=&quot;1.0&quot; encoding=&quot;utf-8&quot;?&gt;
    &lt;LinearLayout xmlns:android=&quot;http://schemas.android.com/apk/res/android&quot;
        android:layout_width=&quot;match_parent&quot;
        android:layout_height=&quot;@dimen/nav_header_height&quot;
        android:background=&quot;@drawable/slide_nav_bar&quot;
        android:gravity=&quot;bottom&quot;
        android:orientation=&quot;vertical&quot;
        android:paddingBottom=&quot;@dimen/activity_vertical_margin&quot;
        android:paddingLeft=&quot;@dimen/activity_horizontal_margin&quot;
        android:paddingRight=&quot;@dimen/activity_horizontal_margin&quot;
        android:paddingTop=&quot;@dimen/activity_vertical_margin&quot;
        android:theme=&quot;@style/ThemeOverlay.AppCompat.Dark&quot;&gt;
    
        &lt;ImageView
            android:id=&quot;@+id/tvHeaderIcon&quot;
            android:layout_width=&quot;60dp&quot;
            android:layout_height=&quot;60dp&quot;
            android:paddingTop=&quot;@dimen/nav_header_vertical_spacing&quot;
            android:src=&quot;@android:drawable/sym_def_app_icon&quot; /&gt;
    
        &lt;TextView
            android:layout_width=&quot;match_parent&quot;
            android:layout_height=&quot;wrap_content&quot;
            android:paddingTop=&quot;@dimen/nav_header_vertical_spacing&quot;
            android:text=&quot;@string/app_name&quot;
            android:textAppearance=&quot;@style/TextAppearance.AppCompat.Body1&quot; /&gt;
    
        &lt;TextView
            android:id=&quot;@+id/tvHeaderName&quot;
            android:layout_width=&quot;wrap_content&quot;
            android:layout_height=&quot;wrap_content&quot; /&gt;
    
    &lt;/LinearLayout&gt;

**MainActivity.java**

    TextView tvHeaderName;

    @Override
        protected void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
            setContentView(R.layout.activity_main);

        tvHeaderName= (TextView) findViewById(R.id.tvHeaderName);
        tvHeaderName.setText(&quot;Saly&quot;);    
    }

How can I do this?

How to change text of a TextView in navigation drawer header?

I have an app published to the alpha channel, with an in-app (un)managed item that costs $1.

When I purchase normally, i.e, use a credit/debit card Google returns the correct developer payload string, but if I choose to &quot;redeem&quot; a promo code and enter said code, Google returns an empty developer payload string, and thus authentication fails in &#39;onIabPurchaseFinished()&#39;.

I should mention that this only occurs if I choose to redeem a code from the app&#39;s purchase flow, and everything works flawlessly if I open Play Store first, redeem the code, and then come back and open the app.

Is this a bug on  Google&#39;s part?

EDIT: The Play Store thing is expected, since it can&#39;t know your payload and the purchase is done without having to check for it.

In-app purchases made via promo codes return empty developer payload string

I am trying to insert values in table. But there is only one value inserted. I am getting an error in log cat when I am trying to insert new values. 

Log cat shows :

    abort at 13 in [INSERT INTO event(totalminutesfrom,dayofweek,title,location,totalminutesto,id) VALUES (?,?,?,?,?,?)]: UNIQUE constraint failed: event.id
    01-24 11:34:39.764 7763-7763/com.example.siddhi.timetablelayout E/SQLiteDatabase: Error inserting totalminutesfrom=694 dayofweek=null title=qxs location=Eded &amp; Mariz totalminutesto=0 id=0
    01-24 11:34:39.764 7763-7763/com.example.siddhi.timetablelayout E/SQLiteDatabase: android.database.sqlite.SQLiteConstraintException: UNIQUE constraint failed: event.id (code 1555)
    01-24 11:34:39.764 7763-7763/com.example.siddhi.timetablelayout E/SQLiteDatabase:     at android.database.sqlite.SQLiteConnection.nativeExecuteForLastInsertedRowId(Native Method)
    01-24 11:34:39.764 7763-7763/com.example.siddhi.timetablelayout E/SQLiteDatabase:     at android.database.sqlite.SQLiteConnection.executeForLastInsertedRowId(SQLiteConnection.java:782)
    01-24 11:34:39.764 7763-7763/com.example.siddhi.timetablelayout E/SQLiteDatabase:     at android.database.sqlite.SQLiteSession.executeForLastInsertedRowId(SQLiteSession.java:788)
    01-24 11:34:39.764 7763-7763/com.example.siddhi.timetablelayout E/SQLiteDatabase:     at android.database.sqlite.SQLiteStatement.executeInsert(SQLiteStatement.java:86)
    01-24 11:34:39.764 7763-7763/com.example.siddhi.timetablelayout E/SQLiteDatabase:     at android.database.sqlite.SQLiteDatabase.insertWithOnConflict(SQLiteDatabase.java:1471)
    01-24 11:34:39.764 7763-7763/com.example.siddhi.timetablelayout E/SQLiteDatabase:     at android.database.sqlite.SQLiteDatabase.insert(SQLiteDatabase.java:1341)
    01-24 11:34:39.764 7763-7763/com.example.siddhi.timetablelayout E/SQLiteDatabase:     at com.example.siddhi.timetablelayout.EventTableHelper.addEvent(EventTableHelper.java:76)
    01-24 11:34:39.764 7763-7763/com.example.siddhi.timetablelayout E/SQLiteDatabase:     at com.example.siddhi.timetablelayout.AddEventActivity$5.onClick(AddEventActivity.java:217)


Its showing error on these two lines while inserting row.

    db.insert(TABLE, null, values);

       db.addEvent(new EventData(eventTitle,dayOfWeek,totalMinutesFrom, totalMinutesTo,location));



EventTableHelper


        
    public class EventTableHelper extends SQLiteOpenHelper {
    
    
        private static final String TABLE = &quot;event&quot;;
        private static final String KEY_ID = &quot;id&quot;;
        private static final String KEY_TITLE = &quot;title&quot;;
        private static final String KEY_LOCATION = &quot;location&quot;;
        private static final String KEY_DAY_OF_WEEK = &quot;dayofweek&quot;;
        private static final String KEY_TOTAL_MINUTES_FROM = &quot;totalminutesfrom&quot;;
        private static final String KEY_TOTAL_MINUTES_TO = &quot;totalminutesto&quot;;
    
    
    
        public EventTableHelper(Context context) {
            super(context, Constants.DATABASE_NAME, null, Constants.DATABASE_VERSION);
            //3rd argument to be passed is CursorFactory instance
        }
    
        // Creating Tables
        @Override
        public void onCreate(SQLiteDatabase db) {
            //createTable(db);
        }
    
        public void createTable(SQLiteDatabase db){
            String CREATE_EVENTS_TABLE = &quot;CREATE TABLE &quot; + TABLE + &quot;(&quot;
                    + KEY_ID + &quot; INTEGER PRIMARY KEY,&quot; + KEY_TITLE + &quot; TEXT,&quot;
                    + KEY_DAY_OF_WEEK +&quot;TEXT&quot; + KEY_TOTAL_MINUTES_FROM +&quot;INTEGER&quot;
                    + KEY_TOTAL_MINUTES_TO + &quot;INTEGER&quot; +  KEY_LOCATION + &quot;TEXT&quot; +  &quot;)&quot;;
    
            db.execSQL(CREATE_EVENTS_TABLE);
    
        }
        // Upgrading database
        @Override
        public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
            // Drop older table if existed
           // db.execSQL(&quot;DROP TABLE IF EXISTS &quot; + TABLE);
    
          //  createTable(db);
    
            // Create tables again
            //onCreate(db);
        }
    
        // code to add the new contact
        public void addEvent(EventData event) {
            SQLiteDatabase db = this.getWritableDatabase();
    
            ContentValues values = new ContentValues();
            values.put(KEY_ID, event.getId());
            values.put(KEY_TITLE,event.getTitle()); // Contact Name
            values.put(KEY_DAY_OF_WEEK,event.getDayofWeek());
            values.put(KEY_TOTAL_MINUTES_FROM,event.getFromMinutes());
            values.put(KEY_TOTAL_MINUTES_TO,event.getToMinutes());
            values.put(KEY_LOCATION,event.getLocation());
            // Inserting Row
            db.insert(TABLE, null, values);
            //2nd argument is String containing nullColumnHack
            db.close(); // Closing database connection
        }
    
        // code to get the single contact
       EventData getEvent(int id) {
            SQLiteDatabase db = this.getReadableDatabase();
    
            Cursor cursor = db.query(TABLE, new String[] { KEY_ID,
                            KEY_TITLE, KEY_DAY_OF_WEEK, KEY_TOTAL_MINUTES_FROM,KEY_TOTAL_MINUTES_TO,KEY_LOCATION }, KEY_ID + &quot;=?&quot;,
                    new String[] { String.valueOf(id) }, null, null, null, null);
            if (cursor != null)
                cursor.moveToFirst();
           EventData eventData = new EventData(Integer.parseInt(cursor.getString(0)),cursor.getString(1), cursor.getString(2),
                   cursor.getInt(3),cursor.getInt(4),cursor.getString(5));
    
            return eventData;
        }
    
    
    
        // code to get all contacts in a list view
        public List&lt;EventData&gt; getAllEvents() {
            List&lt;EventData&gt; conList = new ArrayList&lt;EventData&gt;();
            // Select All Query
            String selectQuery = &quot;SELECT  * FROM &quot; + TABLE;
    
            SQLiteDatabase db = this.getWritableDatabase();
            Cursor cursor = db.rawQuery(selectQuery, null);
    
            // looping through all rows and adding to list
            if (cursor.moveToFirst()) {
                do {
    
                    EventData event = new EventData();
    
                    event.setId(Integer.parseInt(cursor.getString(0)));
                    event.setTitle(cursor.getString(1));
                    event.setDayofWeek(cursor.getString(2));
                    event.setFromMinutes(cursor.getInt(3));
                    event.setToMinutes(cursor.getInt(4));
                    event.setLocation(cursor.getString(5));
                    // Adding contact to list
                    conList.add(event);
                } while (cursor.moveToNext());
            }
    
            // return contact list
            return conList;
        }
    }

How to solve this??

UNIQUE constraint failed: sqlite database : android

I have a Kotlin source file, but I want to translate it to Java.

How can I convert Kotlin to Java source?

How to convert a Kotlin source file to a Java source file

I wanted to know why most variables in Kotlin are underlined. Some files contain a lot of underlining which is very annoying. If I hover my mouse over a variable it doesn&#39;t give any information most of the time. But on some it says &quot;This property has a backing field&quot; or &quot;Value captured in a closure&quot;. Does anybody know how to disable those underlines? Here is a screenshot with what I mean:
[![enter image description here][1]][1]

And realm is then underlined throughout the entire file.


  [1]: http://i.stack.imgur.com/qUQMI.png

Kotlin: Why are most variables underlined in Android Studio and how do I turn that off?

How can I create a Array like we do in java?

    int A[] = new int[N];

How can I do this in Kotlin?

How can I create an array in Kotlin like in Java by just providing a size?

Given some arrays in Kotlin

&lt;!-- language: lang-kotlin --&gt;

    let a = arrayOf(&quot;first&quot;, &quot;second&quot;)
    val b = arrayOf(&quot;first&quot;, &quot;second&quot;)
    val c = arrayOf(&quot;1st&quot;, &quot;2nd&quot;)

Are there built-in functions to the Kotlin std-lib that tests two arrays for (value) equality for each element?

Thus resulting in:

&lt;!-- language: lang-kotlin --&gt;

    a.equals(b) // true
    a.equals(c) // false

`equals()` is actually returning `false` in both cases, but maybe there are built-in functions to Kotlin that one could use?

There is the static function `java.utils.Arrays.deepEquals(a.toTypedArray(), b.toTypedArray())` but I would rather prefer an instance method as it would work better with optionals.


How to compare two arrays in Kotlin?

In Kotlin, a function with at least one argument can be defined either as a regular non-member function or as an [extension function][1] with one argument being a receiver.

As to the scoping, there seems to be no difference: both can be declared inside or outside classes and other functions, and both can or cannot have visibility modifiers equally.

Language reference seems not to recommend using regular functions or extension functions for different situations.

So, my question is: **when do extension functions give advantage over regular non-member ones?** And when regular ones over extensions?

`foo.bar(baz, baq)` vs `bar(foo, baz, baq)`.

Is it just a hint of a function semantics (receiver is definitely in focus) or are there cases when using extensions functions makes code much cleaner or opens up opportunities?


  [1]: https://kotlinlang.org/docs/reference/extensions.html#extension-functions

When should one prefer Kotlin extension functions?

I&#39;ve been working with dagger2 for a while. And I got confused wether to create an own component/module for each Activity/ Fragment. Please help me clarify this:

For example, We have an app, and the app has about 50 screens.
We will implement the code following the MVP pattern and Dagger2 for DI. Suppose that we have 50 activities and 50 presenters. 

In my opinion, usually we should organize the code like this :

1. Create an AppComponent and AppModule which will provide all objects that will be used while the app is open.

		@Module
		public class AppModule {

		    private final MyApplicationClass application;

		    public AppModule(MyApplicationClass application) {
		        this.application = application;
		    }

		    @Provides
		    @Singleton
		    Context provideApplicationContext() {
		        return this.application;
		    }

		    //... and many other providers 

		}

		@Singleton
		@Component( modules = { AppModule.class } )
		public interface AppComponent {

		    Context getAppContext();

		    Activity1Component plus(Activity1Module module);
		    Activity2Component plus(Activity2Module module);

		    //... plus 48 methods for 48 other activities. Suppose that we don&#39;t have any other Scope (like UserScope after user login, ....)

		}

2. Create ActivityScope :

		@Scope
		@Documented
		@Retention(value=RUNTIME)
		public @interface ActivityScope {
		}

3. Create Component and Module for each Activity. Usually I will put them as static classes within the Activity class:

		@Module
		public class Activity1Module {

		    public LoginModule() {
		    }
		    @Provides
		    @ActivityScope
		    Activity1Presenter provideActivity1Presenter(Context context, /*...some other params*/){
		        return new Activity1PresenterImpl(context, /*...some other params*/);
		    }

		}

		@ActivityScope
		@Subcomponent( modules = { Activity1Module.class } )
		public interface Activity1Component {
		    void inject(Activity1 activity); // inject Presenter to the Activity
		}

		// .... Same with 49 remaining modules and components.


Those are just very simple examples to show how I would implement this.

**But a friend of mine just gave me another implementation:**

1. Create PresenterModule which will provide all presenters:

		@Module
		public class AppPresenterModule {

		    @Provides
		    Activity1Presenter provideActivity1Presentor(Context context, /*...some other params*/){
		        return new Activity1PresenterImpl(context, /*...some other params*/);
		    }

		   	@Provides
		    Activity2Presenter provideActivity2Presentor(Context context, /*...some other params*/){
		        return new Activity2PresenterImpl(context, /*...some other params*/);
		    }

		    //... same with 48 other presenters.

		}


2. Create AppModule and AppComponent:


		@Module
		public class AppModule {

		    private final MyApplicationClass application;

		    public AppModule(MyApplicationClass application) {
		        this.application = application;
		    }

		    @Provides
		    @Singleton
		    Context provideApplicationContext() {
		        return this.application;
		    }

		    //... and many other provides 

		}

		@Singleton
		@Component(
		        modules = { AppModule.class,  AppPresenterModule.class }
		)
		public interface AppComponent {

		    Context getAppContext();

		    public void inject(Activity1 activity);
		    public void inject(Activity2 activity);

		    //... and 48 other methods for 48 other activities. Suppose that we don&#39;t have any other Scope (like UserScope after user login, ....)

		}


His explaination is: **He doesn&#39;t have to create components and modules for each activity.**
I think my friends idea is absolutely not good at all, but please correct me if I am wrong. Here are the reasons:

1. **A lot of memory leaks** :
 - **The app will create 50 presenters even if the user has only 2 Activities open.** 
 - **After the user closes an Activity, its presenter will still remain**

2. What happens if I want to create two instances of one Activity ? (how can he create two presenters )

3. It will take a lot of time for the app to initialize (because it has to create many presenters, objects, ...)


**Sorry for a long post, but please help me clarify this for me and my friend, I can&#39;t convince him.**
Your comments will be very appreciated.


/*-----------------------------------------------------------------------*/

Edit after doing a demo. 

First, thanks for @pandawarrior answer.
I should have created a Demo before I asked this question. I hope my conclusion here could help someone else.

1. What my friend has done does not cause memory leaks unless he puts any Scope to the Provides-methods. (For example @Singleton, or @UserScope, ...)
2. We can create many presenters, if the Provides-method doesn&#39;t have any Scope. (So, my second point is wrong, too)
3. Dagger will create the presenters only when they are needed. (So, the app will not take a long time to initialize, I was confused by Lazy Injection)

So, all the reasons I have said above are mostly wrong. But it does not mean that we should follow my friend idea, for two reasons:

1. It&#39;s not good for the source&#39;s architecture, when he inits all presenters in  module / component. (It violates [Interface segregation principle][1], maybe [Single Responsibility][2] priciple, too).

2. When we create a Scope Component, we will know when it&#39;s created and when it&#39;s destroyed which is a huge benefit for avoiding memory leaks. So, for each Activity we should create a Component with an @ActivityScope. Let&#39;s imagine, with my friends implementation, that we forgot to put some Scope in the Provider-method =&gt; memory leaks will occur.

In my opinion, with a small app (just a few screens without many dependencies or with similar dependencies), we could apply my friends idea, but of course it&#39;s not recommended.

Prefer to read more on:
https://stackoverflow.com/questions/28411352/what-determines-the-lifecycle-of-a-component-object-graph-in-dagger-2
https://stackoverflow.com/questions/35314682/dagger2-activity-scope-how-many-modules-components-do-i-need?rq=1

And one more note: If you want to see when the object are destroyed, you can call those of method together and the GC will run immediately:

        System.runFinalization();
        System.gc();

If you use only one of these methods, GC will run later, and you may get wrong results.


  [1]: https://en.wikipedia.org/wiki/Interface_segregation_principle
  [2]: https://en.wikipedia.org/wiki/Single_responsibility_principle

Dagger- Should we create each component and module for each Activity/ Fragment

In my module, in my base Application class 

    component = DaggerCompClassComponent.builder()
                    .classModule(new ModuleClass()).build();


it can not find DaggerCompClassComponent. 

I have on module build.gradle


    apply plugin: &#39;com.neenbedankt.android-apt&#39;
    .........................
    apt &#39;com.google.dagger:dagger-compiler:2.8&#39;
    compile &#39;com.google.dagger:dagger:2.8&#39;
    provided &#39;javax.annotation:jsr250-api:1.0&#39;

and in Project build.gradle, 

     classpath &#39;com.neenbedankt.gradle.plugins:android-apt:1.8&#39;

I have done build / rebuild / clean / restart project. I have a Component class where I inject objects and a ModuleClass where I provide objects to inject.

What can be the cause for not generating Dagger Component . class ?

EDIT:

This is my ModuleClass, adnotated with @Module:

    @Provides
    @Singleton
    public Interceptor provideInterceptor() {
        return new Interceptor() {
            @Override
            public Response intercept(Chain chain) throws IOException {
                Request.Builder builder = chain.request().newBuilder();

                builder.addHeader(&quot;AppName-Android&quot;, BuildConfig.VERSION_NAME + &quot;-&quot; + BuildConfig.VERSION_CODE)
                        .addHeader(&quot;Content-Type&quot;, &quot;application/json&quot;);

                return chain.proceed(builder.build());
            }
        };
    }

    @Provides
    @Singleton
    OkHttpClient provideOkHttpClient(Interceptor interceptor) {
        OkHttpClient.Builder builder = new OkHttpClient.Builder();
        builder.interceptors().add(interceptor);
        return builder.build();
    }

    @Provides
    @Singleton
    Retrofit provideRetrofit(OkHttpClient client) {
        return new Retrofit.Builder()
                .baseUrl(BaseApplication.getRes().getString(R.string.api_base_url))
                .addConverterFactory(GsonConverterFactory.create())
                .client(client)
                .build();
    }

    @Provides
    @Singleton
    WebServiceCall provideWebService(Retrofit retrofit) {
        return retrofit.create(WebServiceCall.class);
    }


And this is my Component Class:

    @Component(modules = ModuleClass.class)
    @Singleton
    public interface ComponentClass {
    
        void inject(Interceptor o);
        void inject(OkHttpClient o);
        void inject(Retrofit o);
        void inject(WebServiceCall o);
    
    }

Dagger 2 component not generated

I am new to Dagger 2. I have 2 Activities, I want to use injected ViewModel for both. Here is my **ViewModuleFactory** :

    @Singleton
    public class ProductViewModelFactory implements ViewModelProvider.Factory {
    
        private final Map&lt;Class&lt;? extends ViewModel&gt;, Provider&lt;ViewModel&gt;&gt; creators;
    
        @Inject
        public ProductViewModelFactory(Map&lt;Class&lt;? extends ViewModel&gt;, Provider&lt;ViewModel&gt;&gt; creators) {
            this.creators = creators;
        }
    
    
        @SuppressWarnings(&quot;unchecked&quot;)
        @Override
        public &lt;T extends ViewModel&gt; T create(Class&lt;T&gt; modelClass) {
            Provider&lt;? extends ViewModel&gt; creator = creators.get(modelClass);
            if (creator == null) {
                for (Map.Entry&lt;Class&lt;? extends ViewModel&gt;, Provider&lt;ViewModel&gt;&gt; entry : creators.entrySet()) {
                    if (modelClass.isAssignableFrom(entry.getKey())) {
                        creator = entry.getValue();
                        break;
                    }
                }
            }
            if (creator == null) {
                throw new IllegalArgumentException(&quot;unknown viewmodel class &quot; + modelClass);
            }
            try {
                return (T) creator.get();
            } catch (Exception e) {
                throw new RuntimeException(e);
            }
        }
    }


My **ViewModelModule**:

    @Module
    abstract class ViewModelModule {
        @Binds
        @IntoMap
        @ViewModelKey(ProductListViewModel.class)
        abstract ViewModel bindProductListViewModel(ProductListViewModel listViewModel);
    
        @Binds
        @IntoMap
        @ViewModelKey(ProductDetailsViewModel.class)
        abstract ViewModel bindProductDetailsViewModel(ProductDetailsViewModel detailsViewModel);
    
        @Binds
        abstract ViewModelProvider.Factory bindViewModelFactory(ProductViewModelFactory factory);
    }

My **ViewModelKey** for mapping:

    @Documented
    @Target({ElementType.METHOD})
    @Retention(RetentionPolicy.RUNTIME)
    @MapKey
    @interface ViewModelKey {
        Class&lt;? extends ViewModel&gt; value();
    }

My **ActivityModule** :

    @Module
    public abstract class ActivityModule {
        abstract ProductListActivity contributeProductListActivity();
        abstract ProductDetailsActivity contributeProductDetailsActivity();
    }

My **AppModule**:

    @Module
    class AppModule {
    
    @Provides
        @Singleton
        RedMartProductService provideRedMartProductService() {
            ........
        }
    
        @Provides
        @Singleton
        ProductListRepository provideProductListRepository(ProductListRepository repository) {
            return repository;
        }
    
        @Provides
        @Singleton
        ProductDetailsRepository provideProductDetailsRepository(ProductDetailsRepository repository) {
            return repository;
        }
    }

My **AppComponent**:

    @Singleton
    @Component(modules = {AndroidInjectionModule.class, ActivityModule.class, AppModule.class})
    public interface AppComponent {
        @Component.Builder
        interface Builder {
            @BindsInstance
            Builder application(Application application);
    
            AppComponent build();
        }
    
        void inject(MartApplication martApp);
    }

My **Application**:

    public class MartApplication extends Application implements HasActivityInjector {
    
        @Inject
        DispatchingAndroidInjector&lt;Activity&gt; dispatchingAndroidInjector;
    
        @Override
        public void onCreate() {
            super.onCreate();
        }
    
        @Override
        public DispatchingAndroidInjector&lt;Activity&gt; activityInjector() {
            return dispatchingAndroidInjector;
        }
    }

In **Activity**: 

    @Inject
    ViewModelProvider.Factory viewModelFactory;
    .......
    AndroidInjection.inject(activity); // Throwing exception
    ListViewModel = ViewModelProviders.of(this, viewModelFactory).get(ProductListViewModel.class);


It is throwing an exception on inject: 

    java.lang.IllegalArgumentException: No injector factory bound for Class&lt;com.mymart.ui.ProductListActivity&gt;

Can anyone help me identify the problem in my code?

.......................................................................

**Edit**: I tried with `ContributesAndroidInjector` as per @azizbekian, but it resulted following error on build: 

        error: [dagger.android.AndroidInjector.inject(T)] Found a dependency cycle:
    com.mymart.repository.ProductListRepository is injected at
    com.mymart.di.AppModule.provideProductListRepository(repository)
    com.mymart.repository.ProductListRepository is injected at
    com.mymart.viewmodel.ProductListViewModel.&lt;init&gt;(productListRepository)
    com.mymart.viewmodel.ProductListViewModel is injected at
    com.mymart.di.ViewModelModule.bindProductListViewModel(listViewModel)
    java.util.Map&lt;java.lang.Class&lt;? extends android.arch.lifecycle.ViewModel&gt;,javax.inject.Provider&lt;android.arch.lifecycle.ViewModel&gt;&gt; is injected at
    com.mymart.viewmodel.ProductViewModelFactory.&lt;init&gt;(creators)
    com.mymart.viewmodel.ProductViewModelFactory is injected at
    com.mymart.di.ViewModelModule.bindViewModelFactory(factory)
    android.arch.lifecycle.ViewModelProvider.Factory is injected at
    com.mymart.ui.ProductListActivity.viewModelFactory
    com.mymart.ui.ProductListActivity is injected at
    dagger.android.AndroidInjector.inject(arg0)

**Edit 2**
After all changes, I am facing again exception:

    java.lang.RuntimeException: Unable to create application com.kaushik.myredmart.MartApplication: java.lang.IllegalStateException: com.kaushik.myredmart.di.AppModule must be set
                                                     at android.app.ActivityThread.handleBindApplication(ActivityThread.java:4710)
                                                     at android.app.ActivityThread.-wrap1(ActivityThread.java)
                                                     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1405)
                                                     at android.os.Handler.dispatchMessage(Handler.java:102)
                                                     at android.os.Looper.loop(Looper.java:148)
                                                     at android.app.ActivityThread.main(ActivityThread.java:5417)
                                                     at java.lang.reflect.Method.invoke(Native Method)
                                                     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
                                                     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)
                                                  Caused by: java.lang.IllegalStateException: com.kaushik.myredmart.di.AppModule must be set
                                                     at com.kaushik.myredmart.di.DaggerAppComponent$Builder.build(DaggerAppComponent.java:180)
                                                     at com.kaushik.myredmart.di.AppInjector.init(AppInjector.java:30)
                                                     at com.kaushik.myredmart.MartApplication.onCreate(MartApplication.java:28)
                                                     at android.app.Instrumentation.callApplicationOnCreate(Instrumentation.java:1013)
                                                     at android.app.ActivityThread.handleBindApplication(ActivityThread.java:4707)
                                                     at android.app.ActivityThread.-wrap1(ActivityThread.java)&#160;
                                                     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1405)&#160;
                                                     at android.os.Handler.dispatchMessage(Handler.java:102)&#160;
                                                     at android.os.Looper.loop(Looper.java:148)&#160;
                                                     at android.app.ActivityThread.main(ActivityThread.java:5417)&#160;
                                                     at java.lang.reflect.Method.invoke(Native Method)

Dagger: IllegalArgumentException: No injector factory bound for Class

I use in kotlin activity ViewPager and I want in Kotlin Fragment use the dagger injection. I have got Error: Dagger does not support injection into private fields.
In Java Fragment the dagger injection work.
Why can i not inject dagger in kotlin faragment ?

in my kotlin activity

    mPagerAdapter = object : FragmentPagerAdapter(supportFragmentManager) {

            private val mFragments = arrayOf(KotlinFragment(), JavaFragment())
            private val mFragmentNames = arrayOf(getString(R.string.cashdocuments), getString(R.string.action_absmysql))

            override fun getItem(position: Int): Fragment {
                return mFragments[position]
            }

            override fun getCount(): Int {
                return mFragments.size
            }

            override fun getPageTitle(position: Int): CharSequence {
                return mFragmentNames[position]
            }
        }

my kotlin fragment

    class KotlinFragment : Fragment()  {


    @Inject
    internal var mSharedPreferences: SharedPreferences? = null

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)

        (activity.application as SamfantozziApp).dgaeacomponent().inject(this)

    }

    override fun onCreateView(inflater: LayoutInflater?, container: ViewGroup?,
                              savedInstanceState: Bundle?): View? {
        super.onCreateView(inflater, container, savedInstanceState)
        val rootView = inflater!!.inflate(R.layout.activity_absserver, container, false)
        
        return rootView
    }
    
    }

messages gradle build

[![enter image description here][1]][1]


  [1]: https://i.stack.imgur.com/WDYxt.png

Content Type	Original Author	Original Content on Stackoverflow
Question	Fábio Carballo	View Question on Stackoverflow
Solution 1 - Android	Jacob	View Answer on Stackoverflow

"Prefer to run the dagger processor over that class instead" in Kotlin

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