Setting a subtitle on my Toolbar from a fragment

问题

I am having some trouble setting the sub-title in my Toolbar from my fragment. I keep getting a Null Pointer Exception at the setSubTitle.

@Override
public void onActivityCreated(Bundle savedInstanceState) {
    super.onActivityCreated(savedInstanceState);

    getActivity().getActionBar().setSubtitle("About"); // NULL POINTER EXCEPTION here
}

Adding the toolbar to the host activity:

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    toolbar = (Toolbar) findViewById(R.id.toolbar);
    if (toolbar != null) {
        Log.w("Rakshak", "Toolbar is not null");

        setSupportActionBar(toolbar);
    }
}

My style.xml

 <style name="AppTheme.Base" parent="Theme.AppCompat.Light.DarkActionBar">
    <item name="colorPrimary">#1A7E99</item>
    <item name="colorPrimaryDark">#16657A</item>
    <item name="android:windowNoTitle">true</item>
    <item name="windowActionBar">false</item>        
</style>

Here is the Logcat:

11-12 11:24:15.580: E/AndroidRuntime(22183): FATAL EXCEPTION: main
11-12 11:24:15.580: E/AndroidRuntime(22183): java.lang.NullPointerException
11-12 11:24:15.580: E/AndroidRuntime(22183):    at com.driverdesignstudio.drvr.About.onActivityCreated(About.java:63)
11-12 11:24:15.580: E/AndroidRuntime(22183):    at android.app.Fragment.performActivityCreated(Fragment.java:1703)
11-12 11:24:15.580: E/AndroidRuntime(22183):    at android.app.FragmentManagerImpl.moveToState(FragmentManager.java:903)
11-12 11:24:15.580: E/AndroidRuntime(22183):    at android.app.FragmentManagerImpl.moveToState(FragmentManager.java:1057)
11-12 11:24:15.580: E/AndroidRuntime(22183):    at android.app.BackStackRecord.run(BackStackRecord.java:694)
11-12 11:24:15.580: E/Androidenter code hereRuntime(22183):     at android.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1435)
11-12 11:24:15.580: E/AndroidRuntime(22183):    at android.app.FragmentManagerImpl$1.run(FragmentManager.java:441)
11-12 11:24:15.580: E/AndroidRuntime(22183):    at android.os.Handler.handleCallback(Handler.java:800)
11-12 11:24:15.580: E/AndroidRuntime(22183):    at android.os.Handler.dispatchMessage(Handler.java:100)
11-12 11:24:15.580: E/AndroidRuntime(22183):    at android.os.Looper.loop(Looper.java:194)
11-12 11:24:15.580: E/AndroidRuntime(22183):    at android.app.ActivityThread.main(ActivityThread.java:5371)
11-12 11:24:15.580: E/AndroidRuntime(22183):    at java.lang.reflect.Method.invokeNative(Native Method)
11-12 11:24:15.580: E/AndroidRuntime(22183):    at java.lang.reflect.Method.invoke(Method.java:525)
11-12 11:24:15.580: E/AndroidRuntime(22183):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:833)
11-12 11:24:15.580: E/AndroidRuntime(22183):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:600)
11-12 11:24:15.580: E/AndroidRuntime(22183):    at dalvik.system.NativeStart.main(Native Method)

Do I have to make interface listeners and listen to the fragment start and stop in my Fragment Activity to set subtitles or is there an easier way to set subtitles in my toolbar from my fragments.

Let me know if you need to see any more of my code.

Cheers.

回答1:

To use the Toolbar and the Appcompat 21, you have to use an AppCompatActivity and use:

((AppCompatActivity) getActivity()).getSupportActionBar().setSubtitle("About");

回答2:

instead of calling getActivity() get the activity reference from the onAttach() lifecycle method of Fragment.

if you are using sherlock actionbar then call getSherlock().getActionBar()

回答3:

You Can Create One Custom Layout For This And Then use in onCreateView method.

private ActionBar actionBar;

OnCreateView method:

actionBar = getActivity().getActionBar();
if (actionBar != null) {
    actionBar.setCustomView(R.layout.actionbar_inner_custom_view);
    actionBar.setDisplayOptions(ActionBar.DISPLAY_SHOW_CUSTOM);
}

回答4:

Declare a variable ActionBar toolbar and use it this way:

toolbar=((AppCompatActivity) getActivity()).getSupportActionBar();

toolbar.setHomeAsUpIndicator(R.drawable.ic_arrow_left);
toolbar.setTitle("Detalhes");

来源：https://stackoverflow.com/questions/26880544/setting-a-subtitle-on-my-toolbar-from-a-fragment