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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:

异常捕获图

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();
        }
    }
}
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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;
        
        ...
    }
}
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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:

  1. 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;
  2. 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() {
        mBinding.recyclerView.setAdapter(null);
        super.onDestroyView();
    }
}
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文章分类
Android
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