ScrollView与RecyclerView冲突及异常情况处理

昨天再写项目的时候，有一个布局需要ScrollView嵌套RecyclerView，效果展示的时候RecyclerView的滑动会出现卡顿的样子，ScrollView也滑动不流畅。产生的原因是ScrollView与RecyclerView冲突引起的。

解决方法：先自定义LinearLayoutManager，重新测量；再自定义ScrollView，横向不拦截，竖向拦截；

（1）.自定义LinearLayoutManager:

public class FullyLinearLayoutManager extends LinearLayoutManager {  
  
    private static final String TAG = FullyLinearLayoutManager.class.getSimpleName();  
  
    public FullyLinearLayoutManager(Context context) {  
        super(context);  
    }  
  
    public FullyLinearLayoutManager(Context context, int orientation, boolean reverseLayout) {  
        super(context, orientation, reverseLayout);  
    }  
  
    private int[] mMeasuredDimension = new int[2];  
  
    @Override  
    public void onMeasure(RecyclerView.Recycler recycler, RecyclerView.State state,  
                          int widthSpec, int heightSpec) {  
  
        final int widthMode = View.MeasureSpec.getMode(widthSpec);  
        final int heightMode = View.MeasureSpec.getMode(heightSpec);  
        final int widthSize = View.MeasureSpec.getSize(widthSpec);  
        final int heightSize = View.MeasureSpec.getSize(heightSpec);  
  
        Log.i(TAG, "onMeasure called. \nwidthMode " + widthMode  
                + " \nheightMode " + heightSpec  
                + " \nwidthSize " + widthSize  
                + " \nheightSize " + heightSize  
                + " \ngetItemCount() " + getItemCount());  
  
        int width = 0;  
        int height = 0;  
        for (int i = 0; i < getItemCount(); i++) {  
            measureScrapChild(recycler, i,  
                    View.MeasureSpec.makeMeasureSpec(i, View.MeasureSpec.UNSPECIFIED),  
                    View.MeasureSpec.makeMeasureSpec(i, View.MeasureSpec.UNSPECIFIED),  
                    mMeasuredDimension);  
  
            if (getOrientation() == HORIZONTAL) {  
                width = width + mMeasuredDimension[0];  
                if (i == 0) {  
                    height = mMeasuredDimension[1];  
                }  
            } else {  
                height = height + mMeasuredDimension[1];  
                if (i == 0) {  
                    width = mMeasuredDimension[0];  
                }  
            }  
        }  
        switch (widthMode) {  
            case View.MeasureSpec.EXACTLY:  
                width = widthSize;  
            case View.MeasureSpec.AT_MOST:  
            case View.MeasureSpec.UNSPECIFIED:  
        }  
  
        switch (heightMode) {  
            case View.MeasureSpec.EXACTLY:  
                height = heightSize;  
            case View.MeasureSpec.AT_MOST:  
            case View.MeasureSpec.UNSPECIFIED:  
        }  
  
        setMeasuredDimension(width, height);  
    }  
  
    private void measureScrapChild(RecyclerView.Recycler recycler, int position, int widthSpec,  
                                   int heightSpec, int[] measuredDimension) {  
        try {  
            View view = recycler.getViewForPosition(0);//fix 动态添加时报IndexOutOfBoundsException  
  
            if (view != null) {  
                RecyclerView.LayoutParams p = (RecyclerView.LayoutParams) view.getLayoutParams();  
  
                int childWidthSpec = ViewGroup.getChildMeasureSpec(widthSpec,  
                        getPaddingLeft() + getPaddingRight(), p.width);  
  
                int childHeightSpec = ViewGroup.getChildMeasureSpec(heightSpec,  
                        getPaddingTop() + getPaddingBottom(), p.height);  
  
                view.measure(childWidthSpec, childHeightSpec);  
                measuredDimension[0] = view.getMeasuredWidth() + p.leftMargin + p.rightMargin;  
                measuredDimension[1] = view.getMeasuredHeight() + p.bottomMargin + p.topMargin;  
                recycler.recycleView(view);  
            }  
        } catch (Exception e) {  
            e.printStackTrace();  
        } finally {  
        }  
    }  
}  

（2）.自定义ScrollView

public class MyScrollview extends ScrollView{
    private int downX;
    private int downY;
    private int mTouchSlop;
    public MyScrollview(Context context) {
        this(context,null);
    }

    public MyScrollview(Context context, AttributeSet attrs) {
        this(context, attrs,-1);
     }

     public MyScrollview(Context context, AttributeSet attrs, int defStyleAttr) {
          super(context, attrs, defStyleAttr);
          mTouchSlop = ViewConfiguration.get(context).getScaledTouchSlop();
     }

    @Override
    public boolean onInterceptTouchEvent(MotionEvent e) {
        int action = e.getAction();
        switch (action) {
            case MotionEvent.ACTION_DOWN:
                downX = (int) e.getRawX();
                downY = (int) e.getRawY();
                break;
            case MotionEvent.ACTION_MOVE:
                int moveY = (int) e.getRawY();
                if (Math.abs(moveY - downY) > mTouchSlop) {
                    return true;
                }
        }
        return super.onInterceptTouchEvent(e);
    }

}

（3）.上面弄好，会出现另外一个问题，RecyclerView条目加载不完全。

如何解决呢？

第一种就是固定recyclerView条目的个数；

第二种就是在recyclerView的外层再嵌套一层相对布局或者线性布局。

        <RelativeLayout
            android:layout_width="match_parent"
            android:layout_weight="1"
            android:layout_height="0dp">
            <android.support.v7.widget.RecyclerView
                android:id="@+id/recycler_front"
                android:layout_width="match_parent"
                android:layout_height="match_parent"/>
        </RelativeLayout>