HierarchyTreeChangeListener.java

import android.view.View;
import android.view.ViewGroup;

/**
 * A {@link ViewGroup.OnHierarchyChangeListener hierarchy change listener} which recursively
 * monitors an entire tree of views.
 */
public final class HierarchyTreeChangeListener implements ViewGroup.OnHierarchyChangeListener {
  /**
   * Wrap a regular {@link ViewGroup.OnHierarchyChangeListener hierarchy change listener} with one
   * that monitors an entire tree of views.
   */
  public static HierarchyTreeChangeListener wrap(ViewGroup.OnHierarchyChangeListener delegate) {
    return new HierarchyTreeChangeListener(delegate);
  }

  private final ViewGroup.OnHierarchyChangeListener delegate;

  private HierarchyTreeChangeListener(ViewGroup.OnHierarchyChangeListener delegate) {
    if (delegate == null) {
      throw new NullPointerException("Delegate must not be null.");
    }
    this.delegate = delegate;
  }

  @Override public void onChildViewAdded(View parent, View child) {
    delegate.onChildViewAdded(parent, child);

    if (child instanceof ViewGroup) {
      ViewGroup childGroup = (ViewGroup) child;
      childGroup.setOnHierarchyChangeListener(this);
      for (int i = 0; i < childGroup.getChildCount(); i++) {
        onChildViewAdded(childGroup, childGroup.getChildAt(i));
      }
    }
  }

  @Override public void onChildViewRemoved(View parent, View child) {
    if (child instanceof ViewGroup) {
      ViewGroup childGroup = (ViewGroup) child;
      for (int i = 0; i < childGroup.getChildCount(); i++) {
        onChildViewRemoved(childGroup, childGroup.getChildAt(i));
      }
      childGroup.setOnHierarchyChangeListener(null);
    }

    delegate.onChildViewRemoved(parent, child);
  }
}