How to fix getActionBar method may produce java.lang.NullPointerException
AndroidAndroid ActionbarToolbarAndroid Problem Overview
I am using a toolbar as my actionbar in an activity. I am trying to add the method getActionBar().setDisplayHomeAsUpEnabled(true);
to the Activity.java file for Up navigation for older devices.
The method produces the following error message in Android Studio:
> Method invocation may produce java.lang.NullPointerException
The Up navigation on the toolbar works fine on newer devices...now I'm trying to figure out how to make sure it will work for older devices. Please advise.
From build.gradle:
dependencies {
compile "com.android.support:appcompat-v7:22.1.0"
}
From AndroidManifest.xml:
android:theme="@style/Theme.AppCompat.NoActionBar.FullScreen"
From styles.xml
<style name="Theme.AppCompat.NoActionBar.FullScreen" parent="AppTheme">
<item name="android:windowNoTitle">true</item>
<item name="windowActionBar">false</item>
<item name="android:windowFullscreen">true</item>
from Activity.java
public class CardViewActivity extends AppCompatActivity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.cardviewinput);
Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
if (toolbar != null) {
// Up navigation to the parent activity for 4.0 and earlier
getActionBar().setDisplayHomeAsUpEnabled(true);
toolbar.setNavigationIcon(R.drawable.ic_action_previous_item);
toolbar.setNavigationOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
onBackPressed();
}
});
}
}
Android Solutions
Solution 1 - Android
Actually Android Studio isn't showing you an "error message", it's just a warning.
Some answers propose the use of an assertion, Dalvik runtime has assertion turned off by default, so you have to actually turn it on for it to actually do something. In this case (assertion is turned off), what you're essentially doing is just tricking Android Studio to not show you the warning. Also, I prefer not to use "assert" in production code.
In my opinion, what you should do is very simple.
if(getActionBar() != null){
getActionBar().setDisplayHomeAsUpEnabled(true);
}
Update: In case you're using the support library version of the Action Bar, you should replace getActionBar() with getSupportActionBar().
if(getSupportActionBar() != null){
getSupportActionBar().setDisplayHomeAsUpEnabled(true);
}
Solution 2 - Android
First off, you need to set the toolbar as the support ActionBar. Then if you're certain it's going to be there all the time, just assert it as != null. This will tell the compiler it won't be null, so the null check passes.
@Override
protected void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
setContentView(R.layout.cardviewinput);
Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
setSupportActionBar(toolbar);
assert getSupportActionBar() != null;
getSupportActionBar().setDisplayHomeAsUpEnabled(true); // it's getSupportActionBar() if you're using AppCompatActivity, not getActionBar()
}
Solution 3 - Android
Thank You Andrew for your answer. If you have a Nav Drawer or something else that uses getSupportActionBar() you need to add assert getSupportActionBar() != null;
Peace,
Example:
@Override
public void setTitle(CharSequence title) {
mTitle = title;
assert getSupportActionBar() != null;
getSupportActionBar().setTitle(mTitle);
}
Solution 4 - Android
Try this :
private ActionBar getActionBar() {
return ((AppCompatActivity) getActivity()).getSupportActionBar();
}
Solution 5 - Android
What I have done is override the getSupportActionBar()
method in my base Activity and add a @NonNull
annotation. This way, I only get one lint warning in the base activity about how I use @NonNull
annotation for something that has a @Nullable
annotation.
@NonNull
@Override
public ActionBar getSupportActionBar() {
// Small hack here so that Lint does not warn me in every single activity about null
// action bar
return super.getSupportActionBar();
}
Solution 6 - Android
I created a generic class such as:
public final class Cast
{
private Cast() {}
/**
* Helps to eliminate annoying NullPointerException lint warning.
*/
@android.support.annotation.NonNull
public static <T> T neverNull(T value)
{
return value;
}
}
then I can use it for any call with NullPointerException warning for which I am sure that it will never happen, e.g.
final ActionBar actionBar = Cast.neverNull(getSupportActionBar());
actionBar.setDisplayHomeAsUpEnabled(true);
actionBar.setHomeButtonEnabled(true);
P.S. don't forget to add "com.android.support:support-annotations" to your gradle file.
Solution 7 - Android
add assert getSupportActionBar() != null;
before getSupportActionBar().setDisplayHomeAsUpEnabled(true);
Solution 8 - Android
if(actionBar != null) {
actionBar.setHomeButtonEnabled(true);
actionBar.setBackgroundDrawable(ContextCompat.getDrawable(mContext,
R.drawable.action_bar_gradient));
}
Solution 9 - Android
use this theme: android:theme="@style/Theme.AppCompat.Light.NoActionBar"
Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
toolbar.setTitle("Title");
setSupportActionBar(toolbar);
ActionBar actionBar = getSupportActionBar();
actionBar.setHomeButtonEnabled(true);
actionBar.setHomeAsUpIndicator(R.drawable.ic_action_previous_item);
actionBar.setDisplayHomeAsUpEnabled(true);
Solution 10 - Android
Alternatively you could assert actionbar to not null.Add the assertion before calling your actionbar as follows
assert getSupportActionBar() != null;
Final snippet would therefore look as follows:
setSupportActionBar((Toolbar) findViewById(R.id.toolbar));
assert getSupportActionBar() != null;
getSupportActionBar().setDisplayHomeAsUpEnabled(true);
Solution 11 - Android
Try this :
setSupportActionBar (toolbar);
if(getSupportActionBar () != null) {
assert getSupportActionBar () != null;
getSupportActionBar ().setDisplayHomeUpEnabled(true);
}
Note that setSupportActionBar(toolbar) should be before getSupportActionBar().
Solution 12 - Android
if(getSupportActionBar() != null){
getSupportActionBar().setDisplayHomeAsUpEnabled(true);
}
OR
Replace the MainActivity extends AppCompatActivity
to public class MainActivity extends AppCompatActivity
Solution 13 - Android
just check getSupportActionBar not equal to null
setSupportActionBar(toolbar);
if(getSupportActionBar() != null) {
getSupportActionBar().setDisplayHomeAsUpEnabled(true);
getSupportActionBar().setTitle("Daily Shopping List");
}
Solution 14 - Android
If you are importing
android.app.ActionBar
you have to use getActionBar()
and if you are importing
android.support.v7.app.ActionBar
use getSupportActionBar()