异步任务不显示按钮单击事件的进度对话框

Question

In my application when i click on Button it sometimes shows the progressdialog and sometimes not show the progressdialog on click of button.

Asynchronous Task code is:

public class LoadData extends AsyncTask<Void, Void, Void>
    {
        ProgressDialog pd;
        @Override
        protected void onPreExecute()
        {
            pd = ProgressDialog.show(MainActivity.this, "", "Loading...");
        }
        @Override
        protected Void doInBackground(Void... params) {
            // TODO Auto-generated method stub
            MainActivity.this.runOnUiThread(new Runnable() {

                public void run() {
                    // TODO Auto-generated method stub
                    LoadActivities(); // function to load data from url 

                }
            });
            return null;
        }
        @Override
        protected void onPostExecute(Void unused) 
        {
            pd.dismiss();    
        }

    }

and on button click event call this as:

btn.setOnClickListener(new View.OnClickListener() {
    public void onClick(View v) {
        new LoadMoreData().execute(null);
    }
});  

Answer 1

the wrong think you are doing is that in doInBackground you use runOnUiThreade . just remove that from your code . It solves your problem.

never use any thread in doInBackground.

Answer 2

Why you have taken run method again in doInBackground , doInBackground method performs computation on a background thread, so no need to take runOnUiThread

      MainActivity.this.runOnUiThread(new Runnable() {

            public void run() {
                // TODO Auto-generated method stub
                LoadActivities(); // function to load data from url 

            }
        });

Just write

protected Boolean doInBackground(final String... args) {
        try {
            LoadActivities(); 
            return true;
        } catch (Exception e) {
            Log.e("tag", "error", e);
            return false;
        }
    }

And also change new LoadMoreData().execute(); don't write null

             btn.setOnClickListener(new View.OnClickListener() {      
                public void onClick(View v) {
                        new LoadMoreData().execute();
                }});   

Answer 3

Nirali's answer seems correct, just to make further explaination and some edits. Progress Dialog will be shown by the time doInBackground method returns value. and in your code it just create another thread, and completes execution, so to display progress dialog by the time LoadActivities exectues, execute this statement in the same thread doInBackground executes, so change to following:

@Override
        protected Void doInBackground(Void... params) {
            // TODO Auto-generated method stub
            MainActivity.this.runOnUiThread(new Runnable() {

            LoadActivities(); // function to load data from url 
            return null;
        }