重写RecyclerView让其在TV上运行

原生RecyclerView使用时的局限性

在手机端使用RecyclerView相信都很简单，但是在TV和盒子端就会出现不少的问题，例如焦点显示不全，无法定位到某个position等等

下面总结下在TV端使用使用RecyclerView时踩过的坑

(一) 解决RecyclerView刷新数据的时候，焦点错乱问题

下面是google官方给出的解决方案

1. adapter调用setHasStableIds(true)方法

2. 重写getItemId()方法,让每个view都有各自的id

public abstract class BaseRecyclerAdapter<VH extends BaseRecyclerViewHolder, T> extends RecyclerView.Adapter<BaseRecyclerViewHolder> {

public LayoutInflater mInflate;

public List<T> mDataList;

public BaseRecyclerAdapter(Context context, List<T> dataList)     {
this.mInflate = LayoutInflater.from(context);
this.mDataList = dataList;
setHasStableIds(true);
}

public void setDataList(List<T> dataList) {
this.mDataList = dataList;
}

public void addDataList(List<T> dataList) {
if (dataList != null && dataList.size()>0) {
this.mDataList.addAll(dataList);
}
}

@Override
public int getItemCount() {
return mDataList != null ? mDataList.size() : 0;
}

@Override
public long getItemId(int position) {
return position;
}

public List<T> getDataList() {
return mDataList;
}

@Override
public void onBindViewHolder(BaseRecyclerViewHolder holder, int position) {
onBindBaseViewHolder((VH) holder, position);
}

public abstract VH onCreateViewHolder(ViewGroup parent, int viewType);

protected abstract void onBindBaseViewHolder(VH viewHolder, int position);

/**
* @param hasStableIds 有多个observer的话会报错
*/
@Override
public void setHasStableIds(boolean hasStableIds) {
super.setHasStableIds(hasStableIds);
}

}

3. RecyclerView的动画必须去掉

setItemAnimator(null);

（二）解决长按遥控器，让RecyclerView快速滑动，焦点错乱问题

1. 由于长按遥控器的时候，RecyclerView找不到findFocusView为null，此时我就把RecyclerView的onKeyUp事件给屏蔽了;

2. 通过FocusFind类找到view，并让view请求焦点；

3.focusFind焦点失败之后，如果是让其滑动item的宽度（左后滑动）或者高度（上下滑动），因为有可能滑到下面还有可能有item，否则RecyclerView将不会继续滑动

@Override
public boolean dispatchKeyEvent(KeyEvent event) {
if (mInterceptLister != null && mInterceptLister.onIntercept(event)) {
return true;
}

boolean result = super.dispatchKeyEvent(event);
View focusView = this.findFocus();
if (focusView == null) {
return result;
} else {

int dy = 0;
int dx = 0;
if (getChildCount() > 0) {
View firstView = this.getChildAt(0);
dy = firstView.getHeight();
dx = firstView.getWidth();
}
if (event.getAction() == KeyEvent.ACTION_UP) {
return true;
} else {
switch (event.getKeyCode()) {
case KeyEvent.KEYCODE_DPAD_RIGHT:
View rightView = FocusFinder.getInstance().findNextFocus(this, focusView, View.FOCUS_RIGHT);
Log.i(TAG, "rightView is null:" + (rightView == null));
if (rightView != null) {
rightView.requestFocus();
return true;
} else {
this.smoothScrollBy(dx, 0);
return true;
}
case KeyEvent.KEYCODE_DPAD_LEFT:
View leftView = FocusFinder.getInstance().findNextFocus(this, focusView, View.FOCUS_LEFT);
Log.i(TAG, "leftView is null:" + (leftView == null));
if (leftView != null) {
leftView.requestFocus();
return true;
} else {
this.smoothScrollBy(-dx, 0);
return true;
}
case KeyEvent.KEYCODE_DPAD_DOWN:
View downView = FocusFinder.getInstance().findNextFocus(this, focusView, View.FOCUS_DOWN);
Log.i(TAG, " downView is null:" + (downView == null));
if (downView != null) {
downView.requestFocus();
return true;
} else {
this.smoothScrollBy(0, dy);
return true;
}
case KeyEvent.KEYCODE_DPAD_UP:
View upView = FocusFinder.getInstance().findNextFocus(this, focusView, View.FOCUS_UP);
Log.i(TAG, "upView is null:" + (upView == null));
if (event.getAction() == KeyEvent.ACTION_UP) {
return true;
} else {
if (upView != null) {
upView.requestFocus();
return true;
} else {
this.smoothScrollBy(0, -dy);
return true;
}

}
}

}

}
return result;
}

（三）解决RecyclerView 定位到某个item不获取焦点问题

RecyclerView仅仅提供了一个smoothScrollToPosition(int position)方法，而且该方法，能滑到指定的position位置，但是该position处的item并没有获取焦点。

想起在使用LeanBack中的RecyclerView时，你会发现它提供了专门定位到某个position，并获取焦点的方法。但是然后沉下心把源码给看了，终于明白了其中的原理，原来它在定位到指定位置的item后，找到目标的item，并让其主动请求焦点。完美解决

(1) RecyclerView的smoothScrollToPosition方法，最终执行的是LayoutManger的smoothScrollToPosition方法。下面是RecyclerView的

smoothScrollToPosition的源代码

public void smoothScrollToPosition(int position) {
if (mLayoutFrozen) {
return;
}
if (mLayout == null) {
Log.e(TAG, "Cannot smooth scroll without a LayoutManager set. " +
"Call setLayoutManager with a non-null argument.");
return;
}
mLayout.smoothScrollToPosition(this, mState, position);
}

(2) RecyclerView弹性滑动是通过SmoothScroller来实现的，SmoothScroller中有onStart和onStop的回调，大胆猜测一下，onStop肯定是滑动结束的回调，于是找到targetView，并让其请求焦点，问题得以解决

/**
* Created by liuyu on 17/2/8.
* fix issue: RecyclerView 进行item定位的时候,item没有获取焦点
*/
public class TvGridLayoutManager extends GridLayoutManager {

public TvGridLayoutManager(Context context, AttributeSet attrs, int defStyleAttr, int defStyleRes) {
super(context, attrs, defStyleAttr, defStyleRes);
}

public TvGridLayoutManager(Context context, int spanCount) {
super(context, spanCount);
}

public TvGridLayoutManager(Context context, int spanCount, int orientation, boolean reverseLayout) {
super(context, spanCount, orientation, reverseLayout);
}

/**
* Base class which scrolls to selected view in onStop().
*/
abstract class GridLinearSmoothScroller extends LinearSmoothScroller {

public GridLinearSmoothScroller(Context context) {
super(context);
}

/**
* 滑动完成后,让该targetPosition 处的item获取焦点
*/
@Override
protected void onStop() {
super.onStop();
View targetView = findViewByPosition(getTargetPosition());

if (targetView != null) {
targetView.requestFocus();
}
super.onStop();
}

}

/**
* RecyclerView的smoothScrollToPosition方法最终会执行smoothScrollToPosition
* @param recyclerView
* @param state
* @param position
*/
@Override
public void smoothScrollToPosition(RecyclerView recyclerView, RecyclerView.State state,
int position) {
GridLinearSmoothScroller linearSmoothScroller =
new GridLinearSmoothScroller(recyclerView.getContext()) {
@Override
public PointF computeScrollVectorForPosition(int targetPosition) {
return computeVectorForPosition(targetPosition);
}
};
linearSmoothScroller.setTargetPosition(position);
startSmoothScroll(linearSmoothScroller);
}

public PointF computeVectorForPosition(int targetPosition) {
return super.computeScrollVectorForPosition(targetPosition);
}
}

为了方便大家我把代码上传到了github：https://github.com/Fredlxy/TVRecyclerView