ScrollView嵌套ListView手势冲突

外层ScrollView，内嵌ListView，都是垂直方向。采用内部拦截法，实现ListView能滚动时则让ListView处理，当ListView滑到顶部或者底部不能滑动时让ScrollView处理

布局
上面有一段文本，中间是ListView，下面还有一段文本

<?xml version="1.0" encoding="utf-8"?>
<org.icegeneral.scroll.MyScrollView xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/sv"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:orientation="vertical">

        <TextView
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:text="AAAAAAAAAA\nAAAAAAAAAA\nAAAAAAAAAA\nAAAAAAAAAA\nAAAAAAAAAA\nAAAAAAAAAA\nAAAAAAAAAA\nAAAAAAAAAA\nAAAAAAAAAA\nAAAAAAAAAA" />

        <org.icegeneral.scroll.MyListView
            android:id="@+id/lv"
            android:layout_width="match_parent"
            android:layout_height="500dp"
            android:background="#888888">

        </org.icegeneral.scroll.MyListView>

        <TextView
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:text="BBBBBBBBBB\nBBBBBBBBBB\nBBBBBBBBBB\nBBBBBBBBBB\nBBBBBBBBBB\nBBBBBBBBBB\nBBBBBBBBBB\nBBBBBBBBBB\nBBBBBBBBBB\nBBBBBBBBBB" />
    </LinearLayout>
</org.icegeneral.scroll.MyScrollView>

MyScrollView
ACTION_DOWN必须让给ListView，ListView才能收到ACTION_MOVE，ListView才能判断自己是否还能滚动
第二点要注意的是：因为ACTION_DOWN让给ListView，那么ACTION_DOWN就无法进入ScrollView的onTouchEvent， 但是ScrollView的滚动需要在ACTION_DOWN阶段做一些准备，所以主动调用了一次

public class MyScrollView extends ScrollView {

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

    @Override
    public boolean onInterceptTouchEvent(MotionEvent ev) {
        if (ev.getAction() == MotionEvent.ACTION_DOWN) {
            onTouchEvent(ev);
            return false;
        }
        return true;
    }

}

MyListView

public class MyListView extends ListView {

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

    private float lastY;

    @RequiresApi(api = Build.VERSION_CODES.KITKAT)
    @Override
    public boolean dispatchTouchEvent(MotionEvent ev) {
        if (ev.getAction() == MotionEvent.ACTION_DOWN) {
            getParent().getParent().requestDisallowInterceptTouchEvent(true);
        } else if (ev.getAction() == MotionEvent.ACTION_MOVE) {
            if (lastY > ev.getY()) {
                // 如果是向上滑动，且不能滑动了，则让ScrollView处理
                if (!canScrollList(1)) {
                    getParent().getParent().requestDisallowInterceptTouchEvent(false);
                    return false;
                }
            } else if (ev.getY() > lastY) {
                // 如果是向下滑动，且不能滑动了，则让ScrollView处理
                if (!canScrollList(-1)) {
                    getParent().getParent().requestDisallowInterceptTouchEvent(false);
                    return false;
                }
            }
        }
        lastY = ev.getY();
        return super.dispatchTouchEvent(ev);
    }

}

Activity

protected void onCreate(Bundle savedInstanceState) {
    ....
    scrollView.smoothScrollTo(0, 0);
}

---

ACTION_DOWN的特殊性
解释下为什么ListView的ACTION_UP无需调用
getParent().getParent().requestDisallowInterceptTouchEvent(false)
来看下ViewGroup源码

@Override
public boolean dispatchTouchEvent(MotionEvent ev) {
    ...
    boolean handled = false;
    if (onFilterTouchEventForSecurity(ev)) {
        final int action = ev.getAction();
        final int actionMasked = action & MotionEvent.ACTION_MASK;

        if (actionMasked == MotionEvent.ACTION_DOWN) {
            cancelAndClearTouchTargets(ev);
            resetTouchState(); //重点是这句
        }

        // Check for interception.
        final boolean intercepted;
        if (actionMasked == MotionEvent.ACTION_DOWN
                || mFirstTouchTarget != null) {
            final boolean disallowIntercept = (mGroupFlags & FLAG_DISALLOW_INTERCEPT) != 0;
            if (!disallowIntercept) {
                intercepted = onInterceptTouchEvent(ev);
                ev.setAction(action); // restore action in case it was changed
            } else {
                intercepted = false;
            }
        } else {
            intercepted = true;
        }
        ...
    }
    ...
}

private void resetTouchState() {
    clearTouchTargets();
    resetCancelNextUpFlag(this);
    mGroupFlags &= ~FLAG_DISALLOW_INTERCEPT; //移除FLAG_DISALLOW_INTERCEPT
    mNestedScrollAxes = SCROLL_AXIS_NONE;
}

所以如果是ACTION_DOWN，会调用resetTouchState()，移除FLAG_DISALLOW_INTERCEPT，所以ACTION_DOWN时，parent一定会进入onInterceptTouchEvent

其他
其实现在都用RecyclerView代替ListView，ScrollView嵌套RecyclerView时，对于手势已经支持得很好，不必自己处理冲突。这个在demo里也有写，做个对比

代码