如何在android中将BitmapDrawable转换为LayerDrawable

Question

This is code snippet.

public boolean onCreateOptionsMenu(Menu menu) {
    // Inflate the main; this adds items to the action bar if it is present.
    getMenuInflater().inflate(R.menu.main, menu);

    MenuItem item = menu.findItem(R.id.action_notifications);
    LayerDrawable icon = (LayerDrawable) item.getIcon();




    // Update LayerDrawable's BadgeDrawable
    Utils2.setBadgeCount(this, icon, mNotificationsCount);
    return true;
}

It is giving error in line

LayerDrawable icon = (LayerDrawable) item.getIcon();

BitmapDrawable cannot be cast to android.graphics.drawable.LayerDrawable

How to cast BitmapDrawable to layer LayerDrawable?

Edit : adding setBadgeCount function.

public static void setBadgeCount(Context context, LayerDrawable icon, int count) {

    BadgeDrawable badge;

    // Reuse drawable if possible
    Drawable reuse = icon.findDrawableByLayerId(R.id.ic_badge);
    if (reuse != null && reuse instanceof BadgeDrawable) {
        badge = (BadgeDrawable) reuse;
    } else {
        badge = new BadgeDrawable(context);
    }

    badge.setCount(count);
    icon.mutate();
    icon.setDrawableByLayerId(R.id.ic_badge, badge);
}

Answer 1

You can only cast the Drawable you get from item.getIcon() to a LayerDrawable if it actually is a LayerDrawable , ie if the icon attribute in the menu definition references a drawable defined by a layer-list

From the the article you mentionned : the menu definition ( menu/menu_home.xml in the article, menu/main.xml in your case)

<menu xmlns:android="http://schemas.android.com/apk/res/android">
    <item android:id="@+id/action_notifications"
        android:title="Notifications"
        android:icon="@drawable/ic_menu_notifications"
        android:showAsAction="always"/>
</menu>

The icon ( drawable/ic_menu_notifications ) referenced should be a layer-list :

<?xml version="1.0" encoding="utf-8"?>
<layer-list xmlns:android="http://schemas.android.com/apk/res/android">
  <item
      android:id="@+id/ic_notification"
      android:drawable="@drawable/ic_action_email"
      android:gravity="center" />
  <!-- set a place holder Drawable so android:drawable isn't null -->
  <item
      android:id="@+id/ic_badge"
      android:drawable="@drawable/ic_action_email" />
</layer-list>

Also one of the layer should have ic_badge as id. This is the layer used by setBadgeCount()