Changed means the data set changed. Individual items updated, or items were added or removed. Invalidated means the data source is no longer available.

I&#39;ve seen the operators `&gt;&gt;` and `&lt;&lt;` in various code that I&#39;ve looked at (none of which I actually understood), but I&#39;m just wondering what they actually do and what some practical uses of them are.

If the shifts are like `x * 2` and `x / 2`, what is the real difference from actually using the `*` and `/` operators? Is there a performance difference?


What does a bitwise shift (left or right) do and what is it used for?

**Note** This is *not* a question about how to implement or emulate duck typing in C#...

For several years I was under the impression that certain C# language features were depdendent on data structures defined in the language itself (which always seemed like an odd chicken &amp; egg scenario to me). For example, I was under the impression that the `foreach` loop was only available to use with types that implemented `IEnumerable`.

Since then I&#39;ve come to understand that the C# compiler uses duck typing to determine whether an object can be used in a foreach loop, looking for a `GetEnumerator` method rather than `IEnumerable`. This makes a lot of sense as it removes the chicken &amp; egg conundrum.

I&#39;m a little confused as to why this isn&#39;t doesn&#39;t seem to be the case with the `using` block and `IDisposable`. Is there any particular reason the compiler can&#39;t use duck typing &amp; look for a `Dispose` method? What&#39;s the reason for this inconsistency?

Perhaps there&#39;s something else going on under the hood with IDisposable?

*Discussing why you would **ever** have an object with a Dispose method that didn&#39;t implement IDisposable is outside the scope of this question :)*

Duck typing in the C# compiler

What is the difference? The android documentation doesn&#39;t have a description for notifyDataSetInvalidated(). I was thinking maybe you call that function to notify all registered listeners, but use notifyDataSetChanged() to not notify them?

Android ListView Adapter notifyDataSetInvalidated() vs notifyDataSetChanged()

<p>What is the difference? The android documentation doesn't have a description for notifyDataSetInvalidated(). I was thinking maybe you call that function to notify all registered listeners, but use notifyDataSetChanged() to not notify them?</p>


I want to make a read-only `EditText` view. The XML to do this code seems to be `android:editable=&quot;false&quot;`, but I want to do this in code. 

How can I do this?

Make EditText ReadOnly

I know this has been asked in many different ways but I still can not seem to delete the gallery image from the default folder. I&#39;m saving the file to the SD card correctly and I can delete that file fine, but the default gallery image file that shows under the folder Camera will not delete.

I would like the image to delete once the activity is returned since the file is already stored on the SD card under `/Coupon2`. 

Any suggestions?

    public void startCamera() {
        Log.d(&quot;ANDRO_CAMERA&quot;, &quot;Starting camera on the phone...&quot;);
    
        mManufacturerText = (EditText) findViewById(R.id.manufacturer);
    	String ManufacturerText = mManufacturerText.getText().toString();
    	String currentDateTimeString = new Date().toString();
    	
        Intent intent = new Intent(MediaStore.ACTION_IMAGE_CAPTURE);
        File filedir = new File(Environment.getExternalStorageDirectory()+&quot;/Coupon2&quot;);
        filedir.mkdirs();
        
        File file = new File(Environment.getExternalStorageDirectory()+&quot;/Coupon2&quot;, ManufacturerText+&quot;-test.png&quot;);
        outputFileUri = Uri.fromFile(file);
        intent.putExtra(MediaStore.EXTRA_OUTPUT, outputFileUri);

        startActivityForResult(intent, CAMERA_PIC_REQUEST);
    }

    protected void onActivityResult(int requestCode, int resultCode, Intent data) {  
    	super.onActivityResult(requestCode, resultCode, data);
        if (requestCode == CAMERA_PIC_REQUEST &amp;&amp; resultCode == -1) {  
            Intent intent = new Intent(&quot;com.android.camera.action.CROP&quot;);
            intent.putExtra(&quot;crop&quot;, &quot;true&quot;);
            intent.putExtra(&quot;scale&quot;, &quot;true&quot;);
            
            intent.putExtra(&quot;return-data&quot;, false);
            intent.setDataAndType(outputFileUri, &quot;image/*&quot;);
            intent.putExtra(MediaStore.EXTRA_OUTPUT, outputFileUri);
            startActivityForResult(intent, CAMERA_CROP_REQUEST);
        }else { 
           	SetImage();
           	saveState();
        }
    }

Deleting a gallery image after camera intent photo taken

I found that I am using a deprecated method for noficitations (notification.setLatestEventInfo())

It says to use Notification.Builder. 

- **How do I use it?**

When I try to create a new instance, it tells me:

    Notification.Builder cannot be resolved to a type



How exactly to use Notification.Builder

I tried using the sample code [in this tutorial](http://web.archive.org/web/20100203080019/http://anddev.org/launch_activity_on_system-emulator_startup-t428.html) but it seems outdated and it did not work. So what changes do I have to make and to what files to have my app start automatically when Android finishes booting up?

How do I start my app when the phone starts on Android?

I have the following Layout which does not work:

&lt;!-- language: lang-xml --&gt;

    &lt;LinearLayout 
        android:orientation=&quot;horizontal&quot; 
        android:layout_width=&quot;match_parent&quot; 
        android:id=&quot;@+id/experienceLayout&quot; 
        android:background=&quot;#ffffff&quot; 
        android:layout_height=&quot;match_parent&quot; 
        android:paddingLeft=&quot;6dp&quot; 
        android:paddingRight=&quot;6dp&quot; 
        android:paddingBottom=&quot;6dp&quot; 
        android:paddingTop=&quot;6dp&quot;&gt;
    
        &lt;TextView 
            android:layout_weight=&quot;1&quot; 
            android:id=&quot;@+id/experienceLabel&quot; 
            android:text=&quot;Experience&quot; 
            android:layout_height=&quot;wrap_content&quot; 
            android:textColor=&quot;#000000&quot; 
            android:layout_width=&quot;wrap_content&quot; 
            android:textStyle=&quot;bold&quot;&gt;
        &lt;/TextView&gt;
    
        &lt;TextView 
            android:id=&quot;@+id/experienceTextView&quot; 
            android:text=&quot;TextView&quot; 
            android:layout_height=&quot;wrap_content&quot; 
            android:textColor=&quot;#000000&quot; 
            android:layout_width=&quot;wrap_content&quot; 
            android:ellipsize=&quot;end&quot; 
            android:lines=&quot;1&quot; 
            android:maxLines=&quot;1&quot; 
            android:singleLine=&quot;true&quot; 
            android:fadeScrollbars=&quot;false&quot;&gt;
        &lt;/TextView&gt;
    
    &lt;/LinearLayout&gt;

How can I show ellipses on my TextView if it is greater than the 1 line?

How can I remove the rows separator in a `ListView`(if possible within the XML layout file where it&#39;s described)?

Remove ListView separator(in the xml layout file)

How can I programmatically scroll to a specific position in a `ListView`?

For example, I have a `String[] {A,B,C,D....}`, and I need to set the top visible item of the `ListView` to the index 21 of my `String[]`.

Programmatically scroll to a specific position in an Android ListView

I have a fairly complex layout (containing RelativeLayouts, TextViews and ImageViews) that I want to place above a listview.  This view should scroll with the listview.

I tried adding the layout as a header to the listview using this code:

    View v = inflater.inflate(R.layout.list_view, container, false);
		
	View header = inflater.inflate(R.layout.header_layout, container, false);
		
	// populate views in the header
		
	mList = (ListView)v.findViewById(R.id.list);
	mList.addHeaderView(header);
	mAdapter = new ReviewsAdapter(getActivity());
	mList.setAdapter(mAdapter); &lt;-- error occurs here

`ReviewsAdapter` is a custom adapter I&#39;ve written which extends `BaseAdapter`.

Upon executing the code, I get this error:

    11-25 17:19:14.802: E/AndroidRuntime(1215): java.lang.ClassCastException: android.widget.FrameLayout$LayoutParams cannot be cast to android.widget.AbsListView$LayoutParams
    11-25 17:19:14.802: E/AndroidRuntime(1215): 	at android.widget.ListView.clearRecycledState(ListView.java:513)
    11-25 17:19:14.802: E/AndroidRuntime(1215): 	at android.widget.ListView.resetList(ListView.java:499)
    11-25 17:19:14.802: E/AndroidRuntime(1215): 	at android.widget.ListView.setAdapter(ListView.java:442)
    11-25 17:19:14.802: E/AndroidRuntime(1215): 	at com.coppi.storefront.product.ProductReviewsFragment.onCreateView(ProductReviewsFragment.java:104)

If I comment out the `mList.addHeaderView(header)` line I do not get the error.  I can also display the header layout without the listview with no problems.

I&#39;m assuming this has something to do with the contents of the header layout but I&#39;m not sure exactly what would be causing it. 

Here is the header xml:

    &lt;RelativeLayout xmlns:android=&quot;http://schemas.android.com/apk/res/android&quot;
    android:layout_width=&quot;match_parent&quot;
    android:layout_height=&quot;match_parent&quot; &gt;

        &lt;RelativeLayout
            android:layout_width=&quot;fill_parent&quot;
            android:layout_height=&quot;fill_parent&quot; &gt;

            &lt;RelativeLayout
                android:id=&quot;@+id/header_section&quot;
                android:layout_width=&quot;fill_parent&quot;
                android:layout_height=&quot;wrap_content&quot;
                android:layout_marginBottom=&quot;@dimen/margin_sides&quot;
                android:background=&quot;@color/pdp_availability_section_background&quot; &gt;

                &lt;TextView
                    android:id=&quot;@+id/header_text&quot;
                    android:layout_width=&quot;fill_parent&quot;
                    android:layout_height=&quot;wrap_content&quot;
                    android:layout_margin=&quot;@dimen/margin_sides&quot;
                    android:paddingBottom=&quot;@dimen/margin_sides&quot;
                    android:text=&quot;@string/ratings_reviews&quot;
                    android:textColor=&quot;#000&quot;
                    android:textSize=&quot;18dp&quot; /&gt;
            &lt;/RelativeLayout&gt;

            &lt;RelativeLayout
                android:id=&quot;@+id/body_section&quot;
                android:layout_width=&quot;fill_parent&quot;
                android:layout_height=&quot;fill_parent&quot;
                android:layout_below=&quot;@id/header_section&quot; &gt;

                &lt;TextView
                    android:id=&quot;@+id/product_title&quot;
                    style=&quot;@style/ProductTitleFont&quot;
                    android:layout_marginBottom=&quot;@dimen/product_title_bottom_margin&quot;
                    android:layout_marginLeft=&quot;@dimen/margin_sides&quot;
                    android:layout_marginRight=&quot;@dimen/margin_sides&quot; /&gt;

                &lt;RelativeLayout
                    android:id=&quot;@+id/attributes_section&quot;
                    android:layout_width=&quot;wrap_content&quot;
                    android:layout_height=&quot;wrap_content&quot;
                    android:layout_below=&quot;@id/product_title&quot;
                    android:layout_centerHorizontal=&quot;true&quot;
                    android:layout_margin=&quot;@dimen/margin_sides&quot; &gt;

                    &lt;LinearLayout
                        android:id=&quot;@+id/overall_section&quot;
                        android:layout_width=&quot;wrap_content&quot;
                        android:layout_height=&quot;wrap_content&quot;
                        android:orientation=&quot;horizontal&quot;
                        android:gravity=&quot;bottom&quot; &gt;

                        &lt;TextView
                            android:id=&quot;@+id/overall_label&quot;
                            style=&quot;@style/ProductTitleFont&quot;
                            android:layout_width=&quot;wrap_content&quot;
                            android:text=&quot;@string/overall_rating&quot; /&gt;

                        &lt;ImageView
                            android:id=&quot;@+id/overall_1&quot;
                            android:layout_width=&quot;wrap_content&quot;
                            android:layout_height=&quot;wrap_content&quot;
                            android:layout_marginLeft=&quot;10dp&quot;
                            android:src=&quot;@drawable/icon_rating_empty&quot; /&gt;

                        &lt;ImageView
                            android:id=&quot;@+id/overall_2&quot;
                            android:layout_width=&quot;wrap_content&quot;
                            android:layout_height=&quot;wrap_content&quot;
                            android:src=&quot;@drawable/icon_rating_empty&quot; /&gt;

                        &lt;ImageView
                            android:id=&quot;@+id/overall_3&quot;
                            android:layout_width=&quot;wrap_content&quot;
                            android:layout_height=&quot;wrap_content&quot;
                            android:src=&quot;@drawable/icon_rating_empty&quot; /&gt;

                        &lt;ImageView
                            android:id=&quot;@+id/overall_4&quot;
                            android:layout_width=&quot;wrap_content&quot;
                            android:layout_height=&quot;wrap_content&quot;
                            android:src=&quot;@drawable/icon_rating_empty&quot; /&gt;

                        &lt;ImageView
                            android:id=&quot;@+id/overall_5&quot;
                            android:layout_width=&quot;wrap_content&quot;
                            android:layout_height=&quot;wrap_content&quot;
                            android:src=&quot;@drawable/icon_rating_empty&quot; /&gt;

                        &lt;TextView
                            android:id=&quot;@+id/overall_score&quot;
                            style=&quot;@style/ProductTitleFont&quot;
                            android:layout_width=&quot;wrap_content&quot;
                            android:layout_marginLeft=&quot;10dp&quot;
                            android:text=&quot;4.6&quot; /&gt;
                    &lt;/LinearLayout&gt;

                    &lt;Button
                        android:id=&quot;@+id/rate_review_button&quot;
                        android:layout_width=&quot;fill_parent&quot;
                        android:layout_height=&quot;wrap_content&quot;
                        android:layout_below=&quot;@id/overall_section&quot;
                        android:layout_marginBottom=&quot;@dimen/margin_sides&quot;
                        android:layout_marginTop=&quot;@dimen/margin_sides&quot;
                        android:text=&quot;@string/rate_review_button_text&quot; /&gt;
                &lt;/RelativeLayout&gt;

                &lt;View
                    android:id=&quot;@+id/attributes_divider&quot;
                    android:layout_width=&quot;fill_parent&quot;
                    android:layout_height=&quot;1dp&quot;
                    android:layout_below=&quot;@id/attributes_section&quot;
                    android:layout_marginBottom=&quot;@dimen/margin_sides&quot;
                    android:layout_marginTop=&quot;@dimen/margin_sides&quot;
                    android:background=&quot;@color/pdp_section_divider&quot; /&gt;

                &lt;TextView
                    android:id=&quot;@+id/review_count&quot;
                    style=&quot;@style/ProductTitleFont&quot;
                    android:layout_width=&quot;wrap_content&quot;
                    android:layout_below=&quot;@id/attributes_divider&quot;
                    android:layout_marginLeft=&quot;@dimen/margin_sides&quot;
                    android:text=&quot;0 &quot; /&gt;

                &lt;TextView
                    style=&quot;@style/ProductTitleFont&quot;
                    android:layout_width=&quot;wrap_content&quot;
                    android:layout_alignBaseline=&quot;@id/review_count&quot;
                    android:layout_marginRight=&quot;@dimen/margin_sides&quot;
                    android:layout_toRightOf=&quot;@id/review_count&quot;
                    android:text=&quot;@string/customer_reviews&quot; /&gt;

                &lt;View
                    android:id=&quot;@+id/review_count_divider&quot;
                    android:layout_width=&quot;fill_parent&quot;
                    android:layout_height=&quot;1dp&quot;
                    android:layout_below=&quot;@id/review_count&quot;
                    android:layout_marginBottom=&quot;@dimen/margin_sides&quot;
                    android:layout_marginTop=&quot;@dimen/margin_sides&quot;
                    android:background=&quot;@color/pdp_section_divider&quot; /&gt;
            &lt;/RelativeLayout&gt;
        &lt;/RelativeLayout&gt;
&lt;/RelativeLayout&gt;

**Update:** I tried reducing the header .xml file to just a single TextView and the problem continues.  So I don&#39;t believe the problem is being cause by something in the xml.

ClassCastException when calling ListView.addHeaderView()?

I want to add `OnLongClickListener` on my list view. Whenever the user long press the item in list some action should be performed, But my code does not catch this listener. Please let me know where I am going wrong. The similar code works for `setOnItemClickListener` very well.


Here is the code :

    listView.setOnItemLongClickListener(new AdapterView.OnItemLongClickListener() {
    
    			public boolean onItemLongClick(AdapterView&lt;?&gt; arg0, View v,
    					int index, long arg3) {
    				// TODO Auto-generated method stub
    				 Log.d(&quot;in onLongClick&quot;);
    			     String str=listView.getItemAtPosition(index).toString();
    				 
    				 Log.d(&quot;long click : &quot; +str);
    				return true;
    			}
    }); 
    			

how to implement a long click listener on a listview

I&#39;ve been looking at creating a stylistically different list view, like many other people, and I started by looking to extend AbsListView. Per the Android doc, AbsListView is:

&gt; Base class that can be used to implement virtualized lists of items. A list does not have a spatial definition here. For instance, subclases of this class can display the content of the list in a grid, in a carousel, as stack, etc.

After some effort and review of the ListView implementation, it looks like it may not be possible to extend AbsListView the way ListView does because of the coupling of the two classes and the inability to access certain package members. I stumbled on this form Romain Guy:

&gt; AbsListView and AbsSpinner are designed to be extended within the
framework. They could also be extended in 3rd party apps but we did
not expose all the necessary protected fields and methods on purpose.
We want to be very careful in how we expose such APIs so as to not get
stuff for future extensions and internal changes. Our current
recommendation is you simply copy/paste the code you need inside your
app.

I started trying to do this but copying AbsListView becomes a rabbit hole of copying in a bunch of other stuff and it really just seems like a losing proposition. I wanted to see if anyone has had success extending AbsListView who could share a methodology.

[1] http://developer.android.com/reference/android/widget/AbsListView.html

[2] https://groups.google.com/forum/?fromgroups#!topic/android-developers/UhbR1tpVvF0

Is it possible to extend AbsListView to make new ListView implementations?

I&#39;m using the v4 compatibility ViewPager in Android.  My FragmentActivity has a bunch of data which is to be displayed in different ways on different pages in my ViewPager.  So far I just have 3 instances of the same ListFragment, but in the future I will have 3 instances of different ListFragments.  The ViewPager is on a vertical phone screen, the lists are not side-by-side.

Now a button on the ListFragment starts an separate full-page activity (via the FragmentActivity), which returns and FragmentActivity modifies the data, saves it, then attempts to update all views in its ViewPager.  It is here, where I am stuck.

    public class ProgressMainActivity extends FragmentActivity
    {
    	MyAdapter mAdapter;
    	ViewPager mPager;
    	
    	@Override
    	public void onCreate(Bundle savedInstanceState)
    	{
    	...
    		mAdapter = new MyAdapter(getSupportFragmentManager());
    
    		mPager = (ViewPager) findViewById(R.id.viewpager);
    		mPager.setAdapter(mAdapter);
    	}
    	
    	@Override
    	protected void onActivityResult(int requestCode, int resultCode, Intent data)
        {
            ...
            updateFragments();
    		...
        }
    	public void updateFragments()
    	{
    		//Attempt 1:
    		//mAdapter.notifyDataSetChanged();
    		//mPager.setAdapter(mAdapter);
    		
    		//Attempt 2:
    		//HomeListFragment fragment = (HomeListFragment) getSupportFragmentManager().findFragmentById(mAdapter.fragId[0]);
    		//fragment.updateDisplay();
    	}
    	
    	public static class MyAdapter extends FragmentPagerAdapter implements
             TitleProvider
    	{
          int[] fragId = {0,0,0,0,0};
          public MyAdapter(FragmentManager fm)
          {
             super(fm);
          }
          @Override
          public String getTitle(int position){
             return titles[position];
          }
          @Override
          public int getCount(){
             return titles.length;
          }
    
          @Override
          public Fragment getItem(int position)
          {
    		
             Fragment frag = HomeListFragment.newInstance(position);
             //Attempt 2:
    		 //fragId[position] = frag.getId();
             return frag;
          }
          
          @Override
          public int getItemPosition(Object object) {
             return POSITION_NONE; //To make notifyDataSetChanged() do something
         }
       }
       
        public class HomeListFragment extends ListFragment
    	{
    	...
    		public static HomeListFragment newInstance(int num)
    		{
    			HomeListFragment f = new HomeListFragment();
    			...
    			return f;
    		}
       ...

Now as you can see, my first attempt was to notifyDataSetChanged on the entire FragmentPagerAdapter, and this showed to update the data sometimes, but others I got an IllegalStateException: Can not perform this action after onSaveInstanceState.  

My second attempt involed trying to call an update function in my ListFragment, but getId in getItem returned 0.  As per the docs I tried by 

&gt; acquiring a reference to the Fragment from FragmentManager, using
&gt; findFragmentById() or findFragmentByTag()

but I don&#39;t know the tag or id of my Fragments! I have an android:id=&quot;@+id/viewpager&quot; for ViewPager, and a android:id=&quot;@android:id/list&quot; for my ListView in the ListFragment layout, but I don&#39;t think these are useful.

So, how can I either:
a) update the entire ViewPager safely in one go (ideally returning the user to the page he was on before) - it is ok that the user see the view change.
Or preferably,
b) call a function in each affected ListFragment to update the ListView manually.

Any help would be gratefully accepted!

Update data in ListFragment as part of ViewPager

In many of the code samples that I find on the internet the `context` is obtained in the constructor of an adapter.

This context is used to get an `inflater` to inflate the views in `getView` method.

My Question is why bother getting the context in the constructor when it can easily be obtained like so
    
            LayoutInflater inflater;
            @Override
            public View getView(int position, View convertView, ViewGroup parent) {
                if(inflater == null){
                Context context = parent.getContext();
                inflater = (LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
                }
                ...
                ...
                
                return convertView;
            }

Also is there any reason not to use the above method because it till now I have not faced any problem in using it .

Getting the android context in an adapter

I always use `LayoutInflater` and `findViewById` for creating new item in the`getView` method of an `Adapter`.

But in many articles people write that `findViewById` is very very slow and strongly recommend to use the View Holder Pattern.

Can anyone explain why `findViewById` is so slow? And why the View Holder Pattern is faster? 


And what should I do if needed to add different items to a `ListView`? Should I create classes for each type?

    static class ViewHolderItem1 {
        TextView textViewItem;
    }
    
    static class ViewHolderItem2 {
        Button btnViewItem;
    }
    static class ViewHolderItem3 {
        Button btnViewItem;
        ImageView imgViewItem;
    }

findViewById vs View Holder Pattern in ListView adapter

I have listview with custom adapter (base adapter). I want to get view from listview by position. I tried `mListView.getChildAt(position)` , but it is not working. How can i get item view by position?

android - listview get item view by position

When I have to use a classic adapter with a [ListView](https://developer.android.com/guide/topics/ui/layout/listview.html), I update my data in the ListView like this:

    myAdapter.swapArray(data);
    
    public swapArray(List&lt;Data&gt; data) {
      clear();
      addAll(data);
      notifyDataSetChanged();
    }

I would like to know what is the best practice for a [RecyclerView](https://developer.android.com/training/material/lists-cards.html). Because in a **RecyclerView** adapter you can&#39;t do a `clear` and `addAll` as in **ListView**.

So I tried just with a `notifyDataSetChanged`, but it didn&#39;t work. 
Then I tried with a swapAdapter on my view:

    List&lt;Data&gt; data = newData;
    
    MyRecyclerAdapter adapter = new MyRecyclerAdapter(data);
    
    // swapAdapter on my recyclerView (instead of a .setAdapter like with a classic listView).
    recyclerViewList.swapAdapter(adapter, false);

But with this last solution, I still have to create a new instance of my adapter and I feel like it&#39;s not the best solution. I should be able just to change my data without a new `MyRecyclerAdapter`.

Content Type	Original Author	Original Content on Stackoverflow
Question	Spidy	View Question on Stackoverflow
Solution 1 - Android	adamp	View Answer on Stackoverflow

Android ListView Adapter notifyDataSetInvalidated() vs notifyDataSetChanged()

Android Problem Overview

Android Solutions

Solution 1 - Android

Duck typing in the C# compiler

What does a bitwise shift (left or right) do and what is it used for?

Attributions