RecyclerView的焦点记忆封装

上一篇中介绍了TV开发中的列表焦点实现
android tv列表焦点记忆实现，是用外部代码控制的方式实现的，比较繁琐，现在介绍用自定义RecyclerView的方式来实现，并增加了其他的功能：限制纵向和横向移出焦点，移入移出焦点的事件监听等。

代码实现如下：


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;
        }
    }

}

代码实现和注释说明如上。
可以直接作为一个recyclerview使用，已经具有了焦点记忆的功能了，不需要在外层增加额外的代码；要增加限制纵向和横向移出焦点，移入移出焦点的事件监听的功能，可以再调用上面的setXXXListener等方法。