从公共类中的 AsyncTask 更新 UI 线程 [英] Updating UI Thread from AsyncTask in public class

问题描述

我正在尝试将一些 AsyncTask 类拆分为公共(单独的)函数，这样我就不必重写这么多代码.我几乎拥有它，除了一个非常重要的方面.AsyncTask 函数通过对服务器进行 php 调用来编译 ArrayList.完成此列表后，我需要更新主 UI 线程上的微调器.我在这里找到了一个非常好的答案，但我有一点很难让它发挥作用.

I'm trying to split off some AsyncTask classes into public (separate) functions so that I'm not having to rewrite so much code. I almost have it, except for one very important aspect. The AsyncTask function compiles an ArrayList by making php calls to a server. When this list is complete, I need to update a spinner on the main UI thread. I found a really nice answer here but I'm having a little difficulty making it work.

这是我所拥有的缩小版本:(请注意，此时，我要做的就是调用 Toast 消息以证明往返工作正常)

Here is a scaled down version of what I have: (note that at this point, all I am trying to do is to call a Toast message to prove that the round trip is working)

这是调用Activity:

public class MyActivity extends Activity implements OnTaskCompleted {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        sg_list = new ArrayList<String>();
        new GetSuperGroups(UpdateAffiliationsPreferences.this, context, "Retrieving Group List...").execute();
    }

    public void onTaskCompleted(ArrayList<String> list) {
        Toast.makeText(getApplicationContext(), "hello from async", Toast.LENGTH_SHORT).show();
    }

}

这是界面:

public interface OnTaskCompleted {
    void onTaskCompleted(ArrayList<String> list);
}

最后，这里是 AsyncTask.请注意，它是一个公共类:

And finally, here is the AsyncTask. Note that it is a Public class:

public class GetSuperGroups extends AsyncTask<String, String, ArrayList<String>> {

    private Activity activity;
    private Context context;
    private String progressMsg;
    private ProgressDialog pDialog;
    private ArrayList<String> sg_list;
    private OnTaskCompleted listener;

    public GetSuperGroups(Activity activity, Context context, String progressMsg) {
        this.activity = activity;
        this.context = context;
        this.progressMsg = progressMsg;
    }

    public void setSuperGroupList (OnTaskCompleted listener){
        this.listener = listener;
    }

    @Override
    protected void onPreExecute() {
        super.onPreExecute();
        pDialog = new ProgressDialog(context);
        pDialog.setMessage(progressMsg);
        pDialog.setIndeterminate(false);
        pDialog.setCancelable(true);
        pDialog.show();
    }

    @Override
    protected ArrayList<String> doInBackground(String... args) {

        sg_list = new ArrayList<String>();
        //make a php call, compile the ArrayList    
        return sg_list;
    }

    protected void onPostExecute(ArrayList<String> sg_list) {
        pDialog.dismiss();
        //this next line causes a null pointer error
        //note that I am throwing away the array list for now
        //all I want to do is prove that I can call the Toast back in the calling Activity
        listener.onTaskCompleted(new ArrayList<String>());
    }
}

推荐答案

只需在 asyncTask constructor 中添加 OnTaskCompleted listener 参数获取超级组.然后在执行 asyncTask 时传递 this.

Just add OnTaskCompleted listener parameter in your asyncTask constructor GetSuperGroups. Then pass this when you execute your asyncTask.

public class MyActivity extends Activity implements OnTaskCompleted {

        @Override
        protected void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
            sg_list = new ArrayList<String>();
            new GetSuperGroups(UpdateAffiliationsPreferences.this, context, "Retrieving Group List...", this).execute();
        }

        public void onTaskCompleted(ArrayList<String> list) {
            Toast.makeText(getApplicationContext(), "hello from async", Toast.LENGTH_SHORT).show();
        }

    }

和

  public class GetSuperGroups extends AsyncTask<String, String, ArrayList<String>> {

        private Activity activity;
        private Context context;
        private String progressMsg;
        private ProgressDialog pDialog;
        private ArrayList<String> sg_list;
        private OnTaskCompleted listener;

        public GetSuperGroups(Activity activity, Context context, String progressMsg, OnTaskCompleted listener) {
            this.activity = activity;
            this.context = context;
            this.progressMsg = progressMsg;
            this.listener = listener;
        }

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