RecyclerView的Adapter中attach和detach探索
问题描述
今天App的日志捕获中收到了一条这样的crash日志:
刚看到这个日志的时候,分析了一下,复现的场景应该是这样的:RecyclerView的Item中一个按钮,点击了之后会发起一个异步请求,开始前会弹出一个ProgressDialog等待,如果这个时候按home键回到了后台,此时不巧被Activity被系统回收的话,就会出现这个问题。debug模式下,开启不保留活动发现能够稳定复现。原因是:异步操作回来的时候,在执行ProgressDialog的dismisss方法的时候,由于Activity已经被回收之后,就相当于这个ProgressDialog(它持有了Activity的Context)所依附的window已经被销毁了,所以会出现这个问题。
代码场景
具体到项目的场景中,我们的项目中一个RecyclerView中对应了很多种type类型,所以引用了MultiType的库来简洁的注册多种类型,这并没什么问题。
问题是:当初为了简单,按钮的点击效果是直接放到了ViewHolder中来处理了。参考代码如下:
public class SongBinder extends ItemViewBinder<SongInfo, SongBinder.ViewHolder> {
@NonNull @Override protected ViewHolder onCreateViewHolder(@NonNull LayoutInflater inflater,
@NonNull ViewGroup parent) {
...
}
@Override protected void onBindViewHolder(@NonNull ViewHolder holder, @NonNull SongInfo item) {
holder.bind(item);
...
}
static class ViewHolder extends RecyclerView.ViewHolder {
private View mView;
private ProgressDialog mProgressDialog;
private CompositeDisposable mDisposables = new CompositeDisposable();
...
public ViewHolder(View itemView) {
super(itemView);
mView = itemView;
...
}
public void bind(SongInfo info) {
mView.setOnClickListener(view -> {
...
// Step1 显示弹窗
showProgress();
mDisposables.add(PlayUtils.playSingleSong().subscribe(status -> {
// Step2 关闭弹窗
dismissProgress();
...
}, throwable -> {
// Step2 关闭弹窗
dismissProgress();
...
}));
});
}
public void showProgress() {
if (mProgressDialog == null) {
mProgressDialog = new LoadingDialog(getContext());
}
mProgressDialog.show();
}
public void dismissProgress() {
if (mProgressDialog != null && mProgressDialog.isShowing()) {
mProgressDialog.dismiss();
}
}
public Context getContext() {
return mView.getContext();
}
}
}
如上面的代码所示,当初为了简便,点击事件的处理放到了ViewHolder中,所以出现了开头所述的问题。因为RecyclerView的Apdater有attach和detach的方法,所以看到这个问题,第一反应是增加这两个方法,然后在detach方法中执行异步任务取消的操作,代码如下:
public class SongBinder extends ItemViewBinder<SongInfo, SongBinder.ViewHolder> {
private CompositeDisposable mDisposables = new CompositeDisposable();
...
@Override protected void onViewAttachedToWindow(@NonNull ViewHolder holder) {
super.onViewAttachedToWindow(holder);
}
@Override protected void onViewDetachedFromWindow(@NonNull ViewHolder holder) {
super.onViewDetachedFromWindow(holder);
// 取消异步操作
mDisposables.clear();
}
class ViewHolder extends RecyclerView.ViewHolder {
private View mView;
private ProgressDialog mProgressDialog;
...
}
}
如代码注释,设置取消的异步任务的操作。本以为这样设置应该可以解决这个问题,但是测试发现,还是会出现上述问题。调试发现,attach方法会执行,但是detach方法并没有被执行到。
后来在这篇文章中找到了一些说明,这里选取部分要点如下:
onAttachedToRecyclerView
is called when the Adapter is set to RecyclerView, after a call to RecyclerView#setAdapter(Adapter) or RecyclerView#swapAdapter(Adapter, boolean). This is quite obvious.onDetachedFromRecyclerView
, on the other hand, is called when current Adapter if going to be replaced by another Adapter (this another ‘Adapter’ can be Null). What is the point here: if you don’t replace the Adapter, this method will never be called. And what happens if an Adapter is never be “detached” from a RecyclerView? Let’s see after I explain about the other couples.onViewAttachedToWindow
is called once RecyclerView or its LayoutManager add a View into RecyclerView (hint: go to RecyclerView source code and search for the following keywords: dispatchChildAttached).onViewDetachedFromWindow
, on opposite, is called when RecyclerView or its LayoutManager detach a View from current Window.
大致意思是说:onViewDetachedFromWindow
只有当它的布局管理把一个子的Item View从当前Window中分离的时候才会调用。总结来说,在以下两种情况下会被调用:
- 显式的调用Adapter的remove方法;
- 重新设置RecyclerView的Adapter;
解决方案
知道了上述原因,想到两种解决方案:
- 比较简单的改法:在Actiivty的onDestroy方法中调用RecyclerView的setAdapter方法,把原来的Adapter设置为null;这样可以保证onDetach的调用,实际测试发现可以解决问题;
- 把所有的点击事件移到Activity中去处理,不要再ViewHolder中处理点击事件。弹对话框的操作也放到Activity中去处理。
项目中为了简单,采用了第一种改法:
@Override protected void onViewDetachedFromWindow(@NonNull ViewHolder holder) {
super.onViewDetachedFromWindow(holder);
// 避免窗体泄漏
holder.dismissProgress();
mDisposables.clear();
}
public class SearchFragment extends Fragment{
...
@Override public void onDestroyView() {
mResultListBinding.recyclerView.setAdapter(null);
super.onDestroyView();
}
}