Android: setBackgroundTintList works on support fab, setSupportBackgroundTintList causes npe

Question

I have a support fab defined as follows:

<android.support.design.widget.FloatingActionButton
        android:id="@+id/somefab"
        android:layout_width="50dp"
        android:layout_height="wrap_content"
        android:layout_centerHorizontal="true"
        android:layout_marginTop="20dp"
        app:elevation="6dp"
        app:rippleColor="@android:color/white"
        />

if I set the backgroundtintlist programmatically like this then it works:

somefab.setBackgroundTintList(ColorStateList.valueOf(Color.GRAY));

however, this is a support fab that should be visible on lower apis, so I want to use the support method:

somefab.setSupportBackgroundTintList(ColorStateList.valueOf(Color.GRAY));

and here already I'm getting a null pointer exception.

    java.lang.RuntimeException: Unable to start activity ComponentInfo{myprojectpath}: java.lang.NullPointerException: Attempt to invoke virtual method 'android.graphics.drawable.Drawable android.graphics.drawable.Drawable$ConstantState.newDrawable()' on a null object reference
  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2416)
  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2476)
  at android.app.ActivityThread.handleRelaunchActivity(ActivityThread.java:4077)
  at android.app.ActivityThread.-wrap15(ActivityThread.java)
  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1350)
  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$MethodAndArgsCaller.run(ZygoteInit.java:726)
  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)
                                                                            Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'android.graphics.drawable.Drawable android.graphics.drawable.Drawable$ConstantState.newDrawable()' on a null object reference
  at android.graphics.drawable.LayerDrawable$ChildDrawable.<init>(LayerDrawable.java:1723)
  at android.graphics.drawable.LayerDrawable$LayerState.<init>(LayerDrawable.java:1792)
  at android.graphics.drawable.RippleDrawable$RippleState.<init>(RippleDrawable.java:998)
  at android.graphics.drawable.RippleDrawable.createConstantState(RippleDrawable.java:989)
  at android.graphics.drawable.RippleDrawable.createConstantState(RippleDrawable.java:988)
  at android.graphics.drawable.LayerDrawable.mutate(LayerDrawable.java:1652)
  at android.graphics.drawable.RippleDrawable.mutate(RippleDrawable.java:975)
  at android.support.v7.widget.AppCompatDrawableManager.tintDrawable(AppCompatDrawableManager.java:773)
  at android.support.v7.widget.AppCompatBackgroundHelper.applySupportBackgroundTint(AppCompatBackgroundHelper.java:115)
  at android.support.v7.widget.AppCompatBackgroundHelper.setSupportBackgroundTintList(AppCompatBackgroundHelper.java:90)
  at android.support.v7.widget.AppCompatImageButton.setSupportBackgroundTintList(AppCompatImageButton.java:99)
  at myproject.myActivity$override.onCreate(myActivity.java:126)
  at myproject.myActivity$override.access$dispatch(myActivity.java)
  at myproject.myActivity.onCreate(myActivity.java:0)
  at android.app.Activity.performCreate(Activity.java:6251)
  at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1107)
  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2369)
  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2476) 
  at android.app.ActivityThread.handleRelaunchActivity(ActivityThread.java:4077) 
  at android.app.ActivityThread.-wrap15(ActivityThread.java) 
  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1350) 
  at android.os.Handler.dispatchMessage(Handler.java:102) 
  at android.os.Looper.loop(Looper.java:148) 
  at android.app.ActivityThread.main(ActivityThread.java:5417) 
  at java.lang.reflect.Method.invoke(Native Method) 
  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726) 
  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616) 

Why does the first method work but not the second?

Answer 1

This should work, I tested it on API 15, 21 and 23:

ViewCompat.setBackgroundTintList(somefab, ColorStateList.valueOf(Color.GRAY));

Why? Going to the source of setSupportBackgroundTintList() shows this:

/**
 * This should be accessed via
 * {@link android.support.v4.view.ViewCompat#setBackgroundTintList(android.view.View, ColorStateList)}
 *
 * @hide
 */
@Override
public void setSupportBackgroundTintList(@Nullable ColorStateList tint) {
    if (mBackgroundTintHelper != null) {
        mBackgroundTintHelper.setSupportBackgroundTintList(tint);
    }
}

It seems the setSupportBackgroundTintList() method should be called indirectly using ViewCompat.setBackgroundTintList(). I tried to call setSupportBackgroundTintList() directly, it worked on API 15 and 21 but crashed on API 23, giving the same NullPointerException you gave.