RecyclerView 在tv端 焦点问题

转自：http://blog.csdn.net/u010072711/article/details/51039967 （收藏）

我们把RecyclerView写成GridView样式，并把RecyclerView的item写成focusable并且有焦点框的时候，我们用焦点滚动RecyclerView的时候会发现RecyclerView的焦点跳转有bug，跟我们想要的焦点跳转规则不一致，会出现的BUG如下图：

黑色方框代表屏幕，我们从左上角的一个item往下按焦点的时候，当需要加载新的一行的时候焦点却跑到了新的一行的最后一个item上面了，（如图，本来是item1获得焦点的，结果跑到item2上面了）。

   这是RecyclerView的一个BUG，记得RecyclerView刚出来的时候滚动都还有点卡顿，到了现在滚动起来还是非常流畅的，比较一个全新的艺术般的空间是需要时间来沉淀的，这个BUG我们可以重写GridLayoutManger来解决。直接看代码：

 package com.wasu.cs.widget;

 import android.content.Context;
 import android.support.v7.widget.GridLayoutManager;
 import android.support.v7.widget.RecyclerView;
 import android.util.AttributeSet;
 import android.view.View;

 /**
  * 自定义GridLayoutManager，修改RecyelerView焦点乱跳的BUG
  * Created by Danxingxi on 2016/4/1.
  */
 public class FocusGridLayoutManager extends GridLayoutManager {


     /**
      * Constructor used when layout manager is set in XML by RecyclerView attribute
      * "layoutManager". If spanCount is not specified in the XML, it defaults to a
      * single column.
      *
      * @param context
      * @param attrs
      * @param defStyleAttr
      * @param defStyleRes
      * @attr ref android.support.v7.recyclerview.R.styleable#RecyclerView_spanCount
      */
     public FocusGridLayoutManager(Context context, AttributeSet attrs, int defStyleAttr, int defStyleRes) {
         super(context, attrs, defStyleAttr, defStyleRes);
     }

     /**
      * Creates a vertical GridLayoutManager
      *
      * @param context   Current context, will be used to access resources.
      * @param spanCount The number of columns in the grid
      */
     public FocusGridLayoutManager(Context context, int spanCount) {
         super(context, spanCount);
     }

     /**
      * @param context       Current context, will be used to access resources.
      * @param spanCount     The number of columns or rows in the grid
      * @param orientation   Layout orientation. Should be {@link #HORIZONTAL} or {@link
      *                      #VERTICAL}.
      * @param reverseLayout When set to true, layouts from end to start.
      */
     public FocusGridLayoutManager(Context context, int spanCount, int orientation, boolean reverseLayout) {
         super(context, spanCount, orientation, reverseLayout);
     }

     /**
      * Return the current number of child views attached to the parent RecyclerView.
      * This does not include child views that were temporarily detached and/or scrapped.
      *
      * @return Number of attached children
      */
     @Override
     public int getChildCount() {
         return super.getChildCount();
     }

     /**
      * Return the child view at the given index
      *
      * @param index Index of child to return
      * @return Child view at index
      */
     @Override
     public View getChildAt(int index) {
         return super.getChildAt(index);
     }

     /**
      * Returns the number of items in the adapter bound to the parent RecyclerView.
      * @return The number of items in the bound adapter
      */
     @Override
     public int getItemCount() {
         return super.getItemCount();
     }

     /**
      * Returns the item View which has or contains focus.
      *
      * @return A direct child of RecyclerView which has focus or contains the focused child.
      */
     @Override
     public View getFocusedChild() {
         return super.getFocusedChild();
     }

     /**
      * Returns the adapter position of the item represented by the given View. This does not
      * contain any adapter changes that might have happened after the last layout.
      *
      * @param view The view to query
      * @return The adapter position of the item which is rendered by this View.
      */
     @Override
     public int getPosition(View view) {
         return super.getPosition(view);
     }

     /**
      * 获取列数
      * @return
      */
     @Override
     public int getSpanCount() {
         return super.getSpanCount();
     }

     /**
      * Called when searching for a focusable view in the given direction has failed for the current content of the RecyclerView.
      * This is the LayoutManager's opportunity to populate views in the given direction to fulfill the request if it can.
      * The LayoutManager should attach and return the view to be focused. The default implementation returns null.
      * 防止当recyclerview上下滚动的时候焦点乱跳
      * @param focused
      * @param focusDirection
      * @param recycler
      * @param state
      * @return
      */
     @Override
     public View onFocusSearchFailed(View focused, int focusDirection, RecyclerView.Recycler recycler, RecyclerView.State state) {

         // Need to be called in order to layout new row/column
         View nextFocus = super.onFocusSearchFailed(focused, focusDirection, recycler, state);

         if (nextFocus == null) {
             return null;
         }
         /**
          * 获取当前焦点的位置
          */
         int fromPos = getPosition(focused);
         /**
          * 获取我们希望的下一个焦点的位置
          */
         int nextPos = getNextViewPos(fromPos, focusDirection);

         return findViewByPosition(nextPos);

     }

     /**
      * Manually detect next view to focus.
      *
      * @param fromPos from what position start to seek.
      * @param direction in what direction start to seek. Your regular {@code View.FOCUS_*}.
      * @return adapter position of next view to focus. May be equal to {@code fromPos}.
      */
     protected int getNextViewPos(int fromPos, int direction) {
         int offset = calcOffsetToNextView(direction);

         if (hitBorder(fromPos, offset)) {
             return fromPos;
         }

         return fromPos + offset;
     }

     /**
      * Calculates position offset.
      *
      * @param direction regular {@code View.FOCUS_*}.
      * @return position offset according to {@code direction}.
      */
     protected int calcOffsetToNextView(int direction) {
         int spanCount = getSpanCount();
         int orientation = getOrientation();

         if (orientation == VERTICAL) {
             switch (direction) {
                 case View.FOCUS_DOWN:
                     return spanCount;
                 case View.FOCUS_UP:
                     return -spanCount;
                 case View.FOCUS_RIGHT:
                     return 1;
                 case View.FOCUS_LEFT:
                     return -1;
             }
         } else if (orientation == HORIZONTAL) {
             switch (direction) {
                 case View.FOCUS_DOWN:
                     return 1;
                 case View.FOCUS_UP:
                     return -1;
                 case View.FOCUS_RIGHT:
                     return spanCount;
                 case View.FOCUS_LEFT:
                     return -spanCount;
             }
         }

         return 0;
     }

     /**
      * Checks if we hit borders.
      *
      * @param from from what position.
      * @param offset offset to new position.
      * @return {@code true} if we hit border.
      */
     private boolean hitBorder(int from, int offset) {
         int spanCount = getSpanCount();

         if (Math.abs(offset) == 1) {
             int spanIndex = from % spanCount;
             int newSpanIndex = spanIndex + offset;
             return newSpanIndex < 0 || newSpanIndex >= spanCount;
         } else {
             int newPos = from + offset;
             return newPos < 0 && newPos >= spanCount;
         }
     }
 }

   分析：在我们从第五行往下按的时候，第六行的view是重新加载的，当新的一行的item还没有加载出来的时候，去找焦点是找不到的，找不到焦点就会调用mLayout.onFocusSearchFailed()方法，

onFocusSearchFailed方法是LayoutManager的方法，默认是返回null的，我们在自定义GridLayoutManager的时候重写此方法即可，具体的处理步骤请看到代码。在RecyclerView源代码中，onFocusSearchFailed是内部抽象类LayoutManager的一个成员方法，默认返回null。