ViewGroups

ViewGroups.java

package com.example.mrenouf.touchtest;

import android.support.v4.view.ViewCompat;
import android.view.View;
import android.view.ViewGroup;
import android.view.ViewParent;

import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.List;

public final class ViewGroups {
  private ViewGroups() {}

  private static final ZComparator Z_COMPARATOR = new ZComparator();
  private static final List<View> tmpViewList = new ArrayList<>();

  public static boolean isTopChildUnder(View child, float x, float y) {
    final ViewParent viewParent = child.getParent();
    if (!(viewParent instanceof ViewGroup)) {
      return true;
    }
    final ViewGroup parent = (ViewGroup) viewParent;
    return getTopChildUnder(parent, x, y) == child;
  }

  public static View getTopChildUnder(ViewGroup parent, float x, float y) {
    // list of siblings ordered by Z, descending (top to bottom)
    getTopSortedChildren(parent, tmpViewList);

    final int childCount = parent.getChildCount();
    for (int i = 0; i < childCount; i++) {
      final View child = tmpViewList.get(i);
      if (child.getVisibility() == View.VISIBLE
          && x >= child.getLeft() && x < child.getRight()
          && y >= child.getTop() && y < child.getBottom()) {
        return child;
      }
    }
    // Somehow outside the bounds of all the child views?
    return null;
  }

  private static void getTopSortedChildren(ViewGroup parent, List<View> out) {
    out.clear();
    final int childCount = parent.getChildCount();
    for (int i = childCount - 1; i >= 0; i--) {
      out.add(parent.getChildAt(i));
    }
    Collections.sort(out, Z_COMPARATOR);
  }

  private static class ZComparator implements Comparator<View> {
    @Override
    public int compare(View lhs, View rhs) {
      final float lz = ViewCompat.getZ(lhs);
      final float rz = ViewCompat.getZ(rhs);
      if (lz > rz) {
        return -1;
      } else if (lz < rz) {
        return 1;
      }
      return 0;
    }
  }
}