ViewGroupUtils.java

package com.mcxtzhang.coordinatordemo;

import android.graphics.Matrix;
import android.graphics.Rect;
import android.graphics.RectF;
import android.view.View;
import android.view.ViewGroup;
import android.view.ViewParent;

/**
 * 介绍：
 * 作者：zhangxutong
 * 邮箱：zhangxutong@imcoming.com
 * 时间： 2016/10/24.
 */

public class ViewGroupUtils {
    /**
     * 获取的任意子View的bound
     * Retrieve the transformed bounding rect of an arbitrary descendant view.
     * This does not need to be a direct child.
     *
     * @param descendant descendant view to reference
     * @param out        rect to set to the bounds of the descendant view
     */
    public static void getDescendantRect(ViewGroup parent, View descendant, Rect out) {
        out.set(0, 0, descendant.getWidth(), descendant.getHeight());
        offsetDescendantRect(parent, descendant, out);
    }

    private static final ThreadLocal<Matrix> sMatrix = new ThreadLocal<>();
    private static final ThreadLocal<RectF> sRectF = new ThreadLocal<>();

    static void offsetDescendantRect(ViewGroup group, View child, Rect rect) {
        Matrix m = sMatrix.get();
        if (m == null) {
            m = new Matrix();
            sMatrix.set(m);
        } else {
            m.reset();
        }
        offsetDescendantMatrix(group, child, m);
        RectF rectF = sRectF.get();
        if (rectF == null) {
            rectF = new RectF();
            sRectF.set(rectF);
        }
        rectF.set(rect);
        m.mapRect(rectF);
        rect.set((int) (rectF.left + 0.5f), (int) (rectF.top + 0.5f),
                (int) (rectF.right + 0.5f), (int) (rectF.bottom + 0.5f));
    }

    static void offsetDescendantMatrix(ViewParent target, View view, Matrix m) {
        final ViewParent parent = view.getParent();
        if (parent instanceof View && parent != target) {
            final View vp = (View) parent;
            offsetDescendantMatrix(target, vp, m);
            m.preTranslate(-vp.getScrollX(), -vp.getScrollY());
        }
        m.preTranslate(view.getLeft(), view.getTop());
        if (!view.getMatrix().isIdentity()) {
            m.preConcat(view.getMatrix());
        }
    }
}