CoordinatorLayout+AppBarLayout+R

问题描述：当AppBarLayout够高时候，快速滑动，在RecyclerView处向相反方向滑动，就会出现弹动抖动现象

问题解决：
1、布局中
<com.google.android.material.appbar.AppBarLayout
android:id="@+id/app_bar_layout"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:background="@color/white"
android:orientation="vertical"
app:layout_behavior="xxxxxx.FixAppBarLayoutBehavior"
app:elevation="0dp"> //内部嵌套的子view就不会有黑线了

app:layout_behavior="xxxxxx.FixAppBarLayoutBehavior" 设置自定义behavior
2、代码中

public class FixAppBarLayoutBehavior extends AppBarLayout.Behavior {
private static final String TAG = "FixBehavior";
private static final int TYPE_FLING = 1;
private boolean isFlinging;
private boolean shouldBlockNestedScroll;

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

@Override
public boolean onInterceptTouchEvent(CoordinatorLayout parent, AppBarLayout child, MotionEvent ev) {
    Log.d(TAG, "onInterceptTouchEvent:" + child.getTotalScrollRange());
    shouldBlockNestedScroll = isFlinging;
    switch (ev.getActionMasked()) {
        case MotionEvent.ACTION_DOWN:
            //手指触摸屏幕的时候停止fling事件
            stopAppbarLayoutFling(child);
            break;
        default:
            break;
    }
    return super.onInterceptTouchEvent(parent, child, ev);
}

/**
 * 反射获取私有的flingRunnable 属性，考虑support 28以后变量名修改的问题
 *
 * @return Field
 */
private Field getFlingRunnableField() throws NoSuchFieldException {
    Class<?> superclass = this.getClass().getSuperclass();
    try {
        // support design 27及一下版本
        Class<?> headerBehaviorType = null;
        if (superclass != null) {
            headerBehaviorType = superclass.getSuperclass();
        }
        if (headerBehaviorType != null) {
            return headerBehaviorType.getDeclaredField("mFlingRunnable");
        } else {
            return null;
        }
    } catch (NoSuchFieldException e) {
        e.printStackTrace();
        // 可能是28及以上版本
        Class<?> headerBehaviorType = superclass.getSuperclass().getSuperclass();
        if (headerBehaviorType != null) {
            return headerBehaviorType.getDeclaredField("flingRunnable");
        } else {
            return null;
        }
    }
}

/**
 * 反射获取私有的scroller 属性，考虑support 28以后变量名修改的问题
 *
 * @return Field
 */
private Field getScrollerField() throws NoSuchFieldException {
    Class<?> superclass = this.getClass().getSuperclass();
    try {
        // support design 27及一下版本
        Class<?> headerBehaviorType = null;
        if (superclass != null) {
            headerBehaviorType = superclass.getSuperclass();
        }
        if (headerBehaviorType != null) {
            return headerBehaviorType.getDeclaredField("mScroller");
        } else {
            return null;
        }
    } catch (NoSuchFieldException e) {
        e.printStackTrace();
        // 可能是28及以上版本
        Class<?> headerBehaviorType = superclass.getSuperclass().getSuperclass();
        if (headerBehaviorType != null) {
            return headerBehaviorType.getDeclaredField("scroller");
        } else {
            return null;
        }
    }
}

/**
 * 停止appbarLayout的fling事件
 *
 * @param appBarLayout
 */
private void stopAppbarLayoutFling(AppBarLayout appBarLayout) {
    //通过反射拿到HeaderBehavior中的flingRunnable变量
    try {
        Field flingRunnableField = getFlingRunnableField();
        Runnable flingRunnable;
        if (flingRunnableField != null) {
            flingRunnableField.setAccessible(true);
            flingRunnable = (Runnable) flingRunnableField.get(this);
            if (flingRunnable != null) {
                Log.d(TAG, "存在flingRunnable");
                appBarLayout.removeCallbacks(flingRunnable);
                flingRunnableField.set(this, null);
            }
        }

        Field scrollerField = getScrollerField();
        if (scrollerField != null) {
            scrollerField.setAccessible(true);
            OverScroller overScroller = (OverScroller) scrollerField.get(this);
            if (overScroller != null && !overScroller.isFinished()) {
                overScroller.abortAnimation();
            }
        }
    } catch (NoSuchFieldException e) {
        e.printStackTrace();
    } catch (IllegalAccessException e) {
        e.printStackTrace();
    }
}

@Override
public boolean onStartNestedScroll(CoordinatorLayout parent, AppBarLayout child,
                                   View directTargetChild, View target,
                                   int nestedScrollAxes, int type) {
    Log.d(TAG, "onStartNestedScroll");
    stopAppbarLayoutFling(child);
    return super.onStartNestedScroll(parent, child, directTargetChild, target,
            nestedScrollAxes, type);
}

@Override
public void onNestedPreScroll(CoordinatorLayout coordinatorLayout,
                              AppBarLayout child, View target,
                              int dx, int dy, int[] consumed, int type) {
    Log.d(TAG, "onNestedPreScroll:" + child.getTotalScrollRange()
            + " ,dx:" + dx + " ,dy:" + dy + " ,type:" + type);
    //type返回1时，表示当前target处于非touch的滑动，
    //该bug的引起是因为appbar在滑动时，CoordinatorLayout内的实现NestedScrollingChild2接口的滑动
    //子类还未结束其自身的fling
    //所以这里监听子类的非touch时的滑动，然后block掉滑动事件传递给AppBarLayout
    if (type == TYPE_FLING) {
        isFlinging = true;
    }
    if (!shouldBlockNestedScroll) {
        super.onNestedPreScroll(coordinatorLayout, child, target, dx, dy, consumed, type);
    }
}

@Override
public void onNestedScroll(CoordinatorLayout coordinatorLayout, AppBarLayout child,
                           View target, int dxConsumed, int dyConsumed, int
                                   dxUnconsumed, int dyUnconsumed, int type) {
    Log.d(TAG, "onNestedScroll: target:" + target.getClass() + " ,"
            + child.getTotalScrollRange() + " ,dxConsumed:"
            + dxConsumed + " ,dyConsumed:" + dyConsumed + " " + ",type:" + type);
    if (!shouldBlockNestedScroll) {
        super.onNestedScroll(coordinatorLayout, child, target, dxConsumed,
                dyConsumed, dxUnconsumed, dyUnconsumed, type);
    }
}

@Override
public void onStopNestedScroll(CoordinatorLayout coordinatorLayout, AppBarLayout abl,
                               View target, int type) {
    Log.d(TAG, "onStopNestedScroll");
    super.onStopNestedScroll(coordinatorLayout, abl, target, type);
    isFlinging = false;
    shouldBlockNestedScroll = false;
}

}

原因分析：behavior用来协调子view间的事件滑动