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; 
    } 
  } 
}