RecyclerView焦点跳转BUG优化的方法

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;     }   } }