如何异步设置recyclerView适配器

Question

I've written a class which looks for specific files in a folder and save their address (plus 3 other attributes) to shared preferences then in my custom adapter i make a call to a method (the method (which is named getAllItems ) reads the data from shared preferences, instantiate new custom objects and add them to a list and returns the list. This is the part that the biggest loading happen) then the adapter uses that list of items to retrieve the address from every single item, generate a Bitmap and show them in a recyclerView this is the error i'm getting:

 E/AndroidRuntime: FATAL EXCEPTION: pool-1-thread-1
        Process: com.amir.example, PID: 4968
        java.util.ConcurrentModificationException
            at java.util.HashMap$HashIterator.nextEntry(HashMap.java:787)
            at java.util.HashMap$KeyIterator.next(HashMap.java:814)
            at com.android.internal.util.XmlUtils.writeSetXml(XmlUtils.java:355)
            at com.android.internal.util.XmlUtils.writeValueXml(XmlUtils.java:693)
            at com.android.internal.util.XmlUtils.writeMapXml(XmlUtils.java:300)
            at com.android.internal.util.XmlUtils.writeMapXml(XmlUtils.java:269)
            at com.android.internal.util.XmlUtils.writeMapXml(XmlUtils.java:235)
            at com.android.internal.util.XmlUtils.writeMapXml(XmlUtils.java:192)
            at android.app.SharedPreferencesImpl.writeToFile(SharedPreferencesImpl.java:600)
            at android.app.SharedPreferencesImpl.-wrap2(SharedPreferencesImpl.java)
            at android.app.SharedPreferencesImpl$2.run(SharedPreferencesImpl.java:515)
            at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1113)
            at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:588)
            at java.lang.Thread.run(Thread.java:818)

now when the number of files are few (like 20 match out of 100 files) the app works fine but when there are too many (like 200 items out of 8000 files) the app crashes

I've tried to load the items into adapter asynchronously: this is in MainActivity.java

 public class AsyncAdapter extends AsyncTask<Void, Void, Void> {
    @Override
    protected Void doInBackground(Void... params) {

        //This line will load the files into shared preferences (DataSource is my sharedPreferences)
        Loader.loadPhoneStickers(adapter.getDataSource()); 

        //this will cause the list that the adapter is attached to, to get updated and load all the items that were added to shared preferences 
        //this method will make a call to getAllItems and notifyItemRangeChanged
        adapter.refresh();
        return null;
    }
}

but the error remains the same whether i do the set the adapter asynchronously (setting the adapter would cause the all the loading to take place)or synchronously

where should i do the loading? will otto be of any helps?

Answer 1

You will need to override this method inside asynctask and to that on postexecute which runs on ui thread. You cannot refresh adapter from ui Thread.

 public class AsyncAdapter extends AsyncTask<Void, Void, Void> {
@Override
protected Void doInBackground(Void... params) {

    //This line will load the files into shared preferences (DataSource is my sharedPreferences)
    Loader.loadPhoneStickers(adapter.getDataSource()); 

    //this will cause the list that the adapter is attached to, to get updated and load all the items that were added to shared preferences 
    //this method will make a call to getAllItems and notifyItemRangeChanged
    return null;
    }

 @Override
 protected void onPostExecute(Void aVoid) {
    super.onPostExecute(aVoid);

      adapter.refresh();
  }
}

Generally when you work in different thread you cannot interact with ui elements. Common practice is to use postExecute in Asynctask.Post execute is called immediately after doInbackground is finished and is called on UI thread where you can do all your Ui related stuff.