FixAppBarLayoutBehavior的小小改进

关于CoordinatorLayout和AppBarLayout 嵌套滑动时抖动的一个原生bug网上有很多文章，我就不细说了，可以看一下这个CoordinatorLayout和AppBarLayout 嵌套滑动时抖动的一个原生bug，里面涉及到的FixAppBarLayoutBehavior这个类，关于反射拿到OverScroller对象实体的地方，需要小小改进一下，如下,此处就做一个小小的记录吧。

package com.msyc.onion.ui.commons.behavior;

import android.content.Context;
import android.util.AttributeSet;
import android.view.MotionEvent;
import android.view.View;
import android.widget.OverScroller;

import androidx.coordinatorlayout.widget.CoordinatorLayout;
import androidx.core.view.ViewCompat;

import com.google.android.material.appbar.AppBarLayout;

import java.lang.reflect.Field;

import static android.view.MotionEvent.ACTION_DOWN;

/**
 * Workaround AppBarLayout.Behavior for https://issuetracker.google.com/66996774
 * 

 * See https://gist.github.com/chrisbanes/8391b5adb9ee42180893300850ed02f2 for
 * example usage.
 * 

 * Change the package name as you wish.
 */
public class FixAppBarLayoutBehavior extends AppBarLayout.Behavior {

    private static final String TAG = "AppBarLayoutBehavior";

    public FixAppBarLayoutBehavior() {
        super();
    }

    public FixAppBarLayoutBehavior(Context context, AttributeSet attrs) {
        super(context, attrs);
    }

    @Override
    public boolean onInterceptTouchEvent(CoordinatorLayout parent, AppBarLayout child, MotionEvent ev) {
        if (ev.getAction() == ACTION_DOWN) {
            Object scroller = getSuperSuperField(this);
            if (scroller != null && scroller instanceof OverScroller) {
                OverScroller overScroller = (OverScroller) scroller;
                overScroller.abortAnimation();
            }
        }
        return super.onInterceptTouchEvent(parent, child, ev);
    }

    private Object getSuperSuperField(Object paramClass) {
        Field field;
        Object object = null;
        try {
            Class cla = (Class) paramClass.getClass().getSuperclass().getSuperclass().getSuperclass();
            field = cla.getDeclaredField("scroller");
            field.setAccessible(true);
            System.out.println("单个对象的某个键的值==反射==" + field.get(paramClass));
            object = field.get(paramClass);

            if (object == null) {
                field = paramClass.getClass().getSuperclass().getSuperclass().getDeclaredField("mScroller");
                field.setAccessible(true);
                object = field.get(paramClass);
            }

        } catch (Exception e) {
            e.printStackTrace();
        }
        return object;
    }

    @Override
    public void onNestedScroll(CoordinatorLayout coordinatorLayout, AppBarLayout child, View target,
                               int dxConsumed, int dyConsumed, int dxUnconsumed, int dyUnconsumed, int type, int[] consume) {
        super.onNestedScroll(coordinatorLayout, child, target, dxConsumed, dyConsumed,
                dxUnconsumed, dyUnconsumed, type, consume);
        stopNestedScrollIfNeeded(dyUnconsumed, child, target, type);
    }

    @Override
    public void onNestedPreScroll(CoordinatorLayout coordinatorLayout, AppBarLayout child,
                                  View target, int dx, int dy, int[] consumed, int type) {
        super.onNestedPreScroll(coordinatorLayout, child, target, dx, dy, consumed, type);
        stopNestedScrollIfNeeded(dy, child, target, type);
    }

    private void stopNestedScrollIfNeeded(int dy, AppBarLayout child, View target, int type) {
        if (type == ViewCompat.TYPE_NON_TOUCH) {
            final int currOffset = getTopAndBottomOffset();
            if ((dy < 0 && currOffset == 0)
                    || (dy > 0 && currOffset == -child.getTotalScrollRange())) {
                ViewCompat.stopNestedScroll(target, ViewCompat.TYPE_NON_TOUCH);
            }
        }
    }
}