1、簡介

想必大家在開發中不可避免的都在使用RecyclerView吧，那麼也應該在NestScrollView中巢狀過RecyclerView吧，但是呢，你會發現當你的Rv和Nsv同向的時候，那麼會遇到滑動失去慣性的問題，這就是我們的問題一，再有當我們的Nsv是固定高度的，那麼會帶來Rv的滑動問題的，這是問題二，以下我們就探討下這兩個問題。

2、滑動慣性解決方案

說來慚愧，我也不知道是啥問題，下面先貼出解決方案，後面知道了再進行補充吧

manager.setSmoothScrollbarEnabled(true);
manager.setAutoMeasureEnabled(true);
//取消recycleview的滑動 
mRvContent.setHasFixedSize(true); 
mRvContent.setNestedScrollingEnabled(false); 
 

3. 解決限定高度的滑動衝突

執行效果:

3.1情景還原

   佈局如下圖所示，整個佈局的主體是個滑動NestScrollView，上部分為內容的主體，固定樣式，而下部分則為在固定高度的LinearLayout中的RecyclerVierw。然後怎麼滑動都沒有反應

    <android.support.v4.widget.NestedScrollView
        android:id="@+id/mNestView"
        android:layout_width="match_parent"
        android:layout_height="match_parent">
        <!--獲取焦點 不然會被Recv搶奪-->
        <LinearLayout
            android:focusable="true"
            android:focusableInTouchMode="true"
            android:orientation="vertical"
            android:layout_width="match_parent"
            android:layout_height="match_parent">
            <View
                android:background="@color/colorAccent"
                android:layout_width="match_parent"
                android:layout_height="200dp"/>
            <RelativeLayout
                android:layout_width="match_parent"
                android:layout_height="520dp">
                <com.example.apple.scrolldemo.confict.TNoConflictRecyclerView
                    android:id="@+id/rv"
                    android:layout_width="match_parent"
                    android:layout_height="match_parent">
                </com.example.apple.scrolldemo.confict.TNoConflictRecyclerView>
            </RelativeLayout>
        </LinearLayout>
    </android.support.v4.widget.NestedScrollView>
 

問題解釋

首先應該清楚的是，NestedScrollview的滑動原理是通過 scrollTo（）來調整並記錄它的滑動位置，而且只要是有拖拽的動作那麼NestedScrollView就會攔截掉滑動的 事件，由它自己去處理滑動，即滾動控制元件。所以我們需要處理的是當RecyclerView滑動的時候，對應的父佈局 NestedScrollVew不允許攔截。

下面貼出NestScrollView的原始碼

    @Override
    public boolean onInterceptTouchEvent(MotionEvent ev) {
        /*
         * This method JUST determines whether we want to intercept the motion.
         * If we return true, onMotionEvent will be called and we do the actual
         * scrolling there.
         */

        /*
        * Shortcut the most recurring case: the user is in the dragging
        * state and he is moving his finger.  We want to intercept this
        * motion.
        */
        final int action = ev.getAction();
        if ((action == MotionEvent.ACTION_MOVE) && (mIsBeingDragged)) {
            return true;
        }

        switch (action & MotionEvent.ACTION_MASK) {
            case MotionEvent.ACTION_MOVE: {
                /*
                 * mIsBeingDragged == false, otherwise the shortcut would have caught it. Check
                 * whether the user has moved far enough from his original down touch.
                 */

                /*
                * Locally do absolute value. mLastMotionY is set to the y value
                * of the down event.
                */
                final int activePointerId = mActivePointerId;
                if (activePointerId == INVALID_POINTER) {
                    // If we don't have a valid id, the touch down wasn't on content.
                    break;
                }

                final int pointerIndex = ev.findPointerIndex(activePointerId);
                if (pointerIndex == -1) {
                    Log.e(TAG, "Invalid pointerId=" + activePointerId
                            + " in onInterceptTouchEvent");
                    break;
                }

                final int y = (int) ev.getY(pointerIndex);
                final int yDiff = Math.abs(y - mLastMotionY);
                if (yDiff > mTouchSlop
                        && (getNestedScrollAxes() & ViewCompat.SCROLL_AXIS_VERTICAL) == 0) {
                    mIsBeingDragged = true;
                    mLastMotionY = y;
                    initVelocityTrackerIfNotExists();
                    mVelocityTracker.addMovement(ev);
                    mNestedYOffset = 0;
                    final ViewParent parent = getParent();
                    if (parent != null) {
                        parent.requestDisallowInterceptTouchEvent(true);
                    }
                }
                break;
            }

            case MotionEvent.ACTION_DOWN: {
                final int y = (int) ev.getY();
                if (!inChild((int) ev.getX(), y)) {
                    mIsBeingDragged = false;
                    recycleVelocityTracker();
                    break;
                }

                /*
                 * Remember location of down touch.
                 * ACTION_DOWN always refers to pointer index 0.
                 */
                mLastMotionY = y;
                mActivePointerId = ev.getPointerId(0);

                initOrResetVelocityTracker();
                mVelocityTracker.addMovement(ev);
                /*
                 * If being flinged and user touches the screen, initiate drag;
                 * otherwise don't. mScroller.isFinished should be false when
                 * being flinged. We need to call computeScrollOffset() first so that
                 * isFinished() is correct.
                */
                mScroller.computeScrollOffset();
                mIsBeingDragged = !mScroller.isFinished();
                startNestedScroll(ViewCompat.SCROLL_AXIS_VERTICAL, ViewCompat.TYPE_TOUCH);
                break;
            }

            case MotionEvent.ACTION_CANCEL:
            case MotionEvent.ACTION_UP:
                /* Release the drag */
                mIsBeingDragged = false;
                mActivePointerId = INVALID_POINTER;
                recycleVelocityTracker();
                if (mScroller.springBack(getScrollX(), getScrollY(), 0, 0, 0, getScrollRange())) {
                    ViewCompat.postInvalidateOnAnimation(this);
                }
                stopNestedScroll(ViewCompat.TYPE_TOUCH);
                break;
            case MotionEvent.ACTION_POINTER_UP:
                onSecondaryPointerUp(ev);
                break;
        }

        /*
        * The only time we want to intercept motion events is if we are in the
        * drag mode.
        */
        return mIsBeingDragged;
    }
 

正確的處理

即是重寫RecyclerView，讓上下滑動時不被攔截掉事件，讓RecyclerView去處理事件。

public class NoConflictRecyclerView  extends RecyclerView{
    private float mStartX;
    private float mStartY;


    public NoConflictRecyclerView(Context context) {
        super(context);
    }

    public NoConflictRecyclerView(Context context, @Nullable AttributeSet attrs) {
        super(context, attrs);
    }

    public NoConflictRecyclerView(Context context, @Nullable AttributeSet attrs, int defStyle) {
        super(context, attrs, defStyle);
    }

    @Override
    public boolean dispatchTouchEvent(MotionEvent ev) {
        switch (ev.getAction())
        {
            case MotionEvent.ACTION_DOWN:
                mStartX = ev.getRawX();
                mStartY = ev.getRawY();
                break;
            case MotionEvent.ACTION_MOVE:
                float endY = ev.getRawY();
                float endX = ev.getRawX();
                float x = endX - mStartX;
                float y = endY - mStartY;
                /* 左右滑動不攔截,上下滑動攔截*/
                if (Math.abs(y) > Math.abs(x))
                {
                    /* 已經在頂部了*/
                    if (y > 0 && !canScrollVertically(-1)){
                        getParent().requestDisallowInterceptTouchEvent(false);
                    }else if (y < 0 && !canScrollVertically(1)){
                        // 不能再上滑了 ========================
                        getParent().requestDisallowInterceptTouchEvent(false);
                    }else {
                        getParent().requestDisallowInterceptTouchEvent(true);
                    }
                }else {
                    getParent().requestDisallowInterceptTouchEvent(false);
                }
                break;
            default:
                break;

        }
        return super.dispatchTouchEvent(ev);
    }


    @Override
    public void onScrolled(int dx, int dy) {
        super.onScrolled(dx, dy);
        Log.e("Rv正在滑動","-dx ="+dx+"---dy ="+dy);
    }

    @Override
    protected void onScrollChanged(int l, int t, int oldl, int oldt) {
        super.onScrollChanged(l, t, oldl, oldt);
    }
}

4. 解決recycleview搶佔焦點

不管NestScrollView的內容是什麼，會自動跳轉到recycleview顯示 

1）給NestScrollView節點新增 
android:focusableInTouchMode="true" 
2）給NestScrollView下的包裹滑動內容的layout新增 
android:descendantFocusability="blocksDescendants"

應用場景: 當NestedScrollView內建了RecyclerView 你期望NestedScrollView獲得焦點時，頂部展開。
該節點的viewgroup(也就是NestScrollView)會優先其子類控制元件而獲取到焦點。

左邊是不處理RecyclerView獲得滑動焦點的效果；

右邊是處理郭RecyclerView失去焦點,且NestedScrollView獲得焦點的情況；

效果還是很顯然易見的，希望對大家有幫助。