Question

I have inner class as broadcast receiver:

public class ManualBacklightReceiver extends BroadcastReceiver {

    public static final String ACTION_MANUAL_BACKLIGHT = "com.android.systemui.statusbar.powerwidget.MANUAL_BACKLIGHT";

    public ManualBacklightReceiver() {
    }

    @Override
    public void onReceive(Context context, Intent intent) {
        Log.d("ManualBacklightReceiver", intent.getAction());
    }

};

AndroidManifest:

<receiver android:name=".statusbar.powerwidget.PowerWidgetGrid$ManualBacklightReceiver">
        <intent-filter>
            <action android:name="com.android.systemui.statusbar.powerwidget.MANUAL_BACKLIGHT"/>
        </intent-filter>            
    </receiver>

And when I send the intent with this code:
Intent intent = new Intent();

intent.setAction("com.android.systemui.statusbar.powerwidget.MANUAL_BACKLIGHT");
intent.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
mContext.sendBroadcast(intent);

I get these exceptions:

java.lang.RuntimeException: Unable to instantiate receiver com.android.systemui.statusbar.powerwidget.PowerWidgetGrid$ManualBacklightReceiver:
java.lang.InstantiationException: can't instantiate class com.android.systemui.statusbar.powerwidget.PowerWidgetGrid$ManualBacklightReceiver; no empty constructor
Caused by: java.lang.InstantiationException: can't instantiate class com.android.systemui.statusbar.powerwidget.PowerWidgetGrid$ManualBacklightReceiver; no empty constructor

But I have an empty constructor! Why it doesn’t work?

Answer 1

You need to declare your inner class as static. Otherwise, an inner class is associated with an instance of your outer class.

Check out the Java Nested Classes tutorial for details. Here is a snippet:

An instance of InnerClass can exist only within an instance of
OuterClass and has direct access to the methods and fields of its
enclosing instance. The next figure illustrates this idea.

and:

A nested class is a member of its enclosing class. Non-static nested
classes (inner classes) have access to other members of the enclosing
class, even if they are declared private. Static nested classes do not
have access to other members of the enclosing class. As a member of
the OuterClass, a nested class can be declared private, public,
protected, or package private. (Recall that outer classes can only be
declared public or package private.)