Android RecyclerView的焦点记忆封装

import android.content.Context;
import android.support.annotation.Nullable;
import android.support.v7.widget.RecyclerView;
import android.util.AttributeSet;
import android.util.Log;
import android.view.KeyEvent;
import android.view.View;
import android.view.ViewGroup;
import java.util.ArrayList;
public class FocusKeepRecyclerView extends RecyclerView {
  private static final String TAG = FocusKeepRecyclerView.class.getSimpleName();
  //是否可以纵向移出
  private boolean mCanFocusOutVertical = true;
  //是否可以横向移出
  private boolean mCanFocusOutHorizontal = true;
  //焦点移出recyclerview的事件监听
  private FocusLostListener mFocusLostListener;
  //焦点移入recyclerview的事件监听
  private FocusGainListener mFocusGainListener;
  //默认第一次选中第一个位置
  private int mCurrentFocusPosition = 0;

  public FocusKeepRecyclerView(Context context) {
    this(context, null);
  }

  public FocusKeepRecyclerView(Context context, @Nullable AttributeSet attrs) {
    this(context, attrs, 0);
  }

  public FocusKeepRecyclerView(Context context, @Nullable AttributeSet attrs, int defStyle) {
    super(context, attrs, defStyle);
    setDescendantFocusability(ViewGroup.FOCUS_AFTER_DESCENDANTS);
    setChildrenDrawingOrderEnabled(true);
    setItemAnimator(null);
    this.setFocusable(true);
  }

  public boolean isCanFocusOutVertical() {
    return mCanFocusOutVertical;
  }

  public void setCanFocusOutVertical(boolean canFocusOutVertical) {
    mCanFocusOutVertical = canFocusOutVertical;
  }

  public boolean isCanFocusOutHorizontal() {
    return mCanFocusOutHorizontal;
  }

  public void setCanFocusOutHorizontal(boolean canFocusOutHorizontal) {
    mCanFocusOutHorizontal = canFocusOutHorizontal;
  }

  @Override
  public View focusSearch(int direction) {
    return super.focusSearch(direction);
  }

  //覆写focusSearch寻焦策略
  @Override
  public View focusSearch(View focused, int direction) {
    Log.i(TAG, "focusSearch " + focused + ",direction= " + direction);
    View view = super.focusSearch(focused, direction);
    if (focused == null) {
      return view;
    }
    if (view != null) {
  //该方法返回焦点view所在的父view,如果是在recyclerview之外，就会是null.所以根据是否是null,来判断是否是移出了recyclerview
      View nextFocusItemView = findContainingItemView(view);
      if (nextFocusItemView == null) {
        if (!mCanFocusOutVertical && (direction == View.FOCUS_DOWN || direction == View.FOCUS_UP)) {
          //屏蔽焦点纵向移出recyclerview
          return focused;
        }
        if (!mCanFocusOutHorizontal && (direction == View.FOCUS_LEFT || direction == View.FOCUS_RIGHT)) {
          //屏蔽焦点横向移出recyclerview
          return focused;
        }
       //调用移出的监听
        if (mFocusLostListener != null) {
          mFocusLostListener.onFocusLost(focused, direction);
        }
        return view;
      }
    }
    return view;
  }

  public void setFocusLostListener(FocusLostListener focusLostListener) {
    this.mFocusLostListener = focusLostListener;
  }

  public interface FocusLostListener {
    void onFocusLost(View lastFocusChild, int direction);
  }

  public void setGainFocusListener(FocusGainListener focusListener) {
    this.mFocusGainListener = focusListener;
  }

  public interface FocusGainListener {
    void onFocusGain(View child, View focued);
  }

  @Override
  public void requestChildFocus(View child, View focused) {
    Log.i(TAG, "nextchild= " + child + ",focused = " + focused);
    if (!hasFocus()) {
      //recyclerview 子view 重新获取焦点，调用移入焦点的事件监听
      if (mFocusGainListener != null) {
        mFocusGainListener.onFocusGain(child, focused);
      }
    }
    super.requestChildFocus(child, focused);//执行过super.requestChildFocus之后hasFocus会变成true
    mCurrentFocusPosition = getChildViewHolder(child).getAdapterPosition();
    Log.i(TAG,"focusPos = "+mCurrentFocusPosition);
  }

 //实现焦点记忆的关键代码
  @Override
  public void addFocusables(ArrayList<View> views, int direction, int focusableMode) {
    View view = null;
    if (this.hasFocus() || mCurrentFocusPosition < 0 || (view = getLayoutManager().findViewByPosition(mCurrentFocusPosition)) == null) {
      super.addFocusables(views,direction,focusableMode);
    }else if(view.isFocusable()){
//将当前的view放到Focusable views列表中，再次移入焦点时会取到该view,实现焦点记忆功能
      views.add(view);
    }else{
      super.addFocusables(views,direction,focusableMode);
    }
  }
  
  /**
   * 控制当前焦点最后绘制，防止焦点放大后被遮挡
   * 原顺序123456789，当4是focus时，绘制顺序变为123567894
   * @param childCount
   * @param i
   * @return
   */
  @Override
  protected int getChildDrawingOrder(int childCount, int i) {
    View focusedChild = getFocusedChild();
    Log.i(TAG,"focusedChild ="+focusedChild);
    if(focusedChild== null){
      return super.getChildDrawingOrder(childCount, i);
    }else{
      int index = indexOfChild(focusedChild);
      Log.i(TAG, " index = " + index + ",i=" + i + ",count=" + childCount);
      if(i == childCount-1){
        return index;
      }
      if(i<index){
        return i;
      }
      return i+1;
    }
  }
}