Android: ProgressDialog doesn't show

问题:

I'm trying to create a ProgressDialog for an Android-App (just a simple one showing the user that stuff is happening, no buttons or anything) but I can't get it right. I've been through forums and tutorials as well as the Sample-Code that comes with the SDK, but to no avail.

This is what I got:

    btnSubmit.setOnClickListener(new View.OnClickListener() {
      public void onClick(View view) {
        (...)
          ProgressDialog pd = new ProgressDialog(MyApp.this);
          pd.setProgressStyle(ProgressDialog.STYLE_HORIZONTAL);
          pd.setMessage("Working...");
          pd.setIndeterminate(true);
          pd.setCancelable(false);

          // now fetch the results
          (...long time calculations here...)

          // remove progress dialog
          pd.dismiss();

I've also tried adding pd.show(); and messed around with the parameter in new ProgressDialog resulting in nothing at all (except errors that the chosen parameter won't work), meaning: the ProgressDialog won't ever show up. The app just keeps running as if I never added the dialog.

I don't know if I'm creating the dialog at the right place, I moved it around a bit but that, too, didnt't help. Maybe I'm in the wrong context? The above code is inside private ViewGroup _createInputForm() in MyApp.

Any hint is appreciated,

回答1:

you have to call pd.show before the long calculation starts and then the calculation has to run in a separate thread. A soon as this thread is finished, you have to call pd.dismiss() to close the prgoress dialog.

here you can see an example:

the progressdialog is created and displayed and a thread is called to run a heavy calculation:

@Override
    public void onClick(View v) {
       pd = ProgressDialog.show(lexs, "Search", "Searching...", true, false);
       Search search = new Search(   ...   );
       SearchThread searchThread = new SearchThread(search);
       searchThread.start();
    }

and here the thread:

private class SearchThread extends Thread {

        private Search search;

        public SearchThread(Search search) {
            this.search = search;
        }

        @Override
        public void run() {         
            search.search();
            handler.sendEmptyMessage(0);
        }

        private Handler handler = new Handler() {

            @Override
            public void handleMessage(Message msg) {
                displaySearchResults(search);
                pd.dismiss();
            }
        };
    }

回答2:

I am giving you a solution for it, try this... First define the Progress Dialog in the Activity before onCreate() method

private ProgressDialog progressDialog;

Now in the onCreate method you might have the Any button click on which you will change the Activity on any action. Just set the Progress Bar there.

progressDialog = ProgressDialog.show(FoodDriveModule.this, "", "Loading...");

Now use thread to handle the Progress Bar to Display and hide

new Thread() 
{
    public void run() 
   {
       try
       {
           sleep(1500); 
           // do the background process or any work that takes time to see progress dialog
       }
       catch (Exception e)
       {
           Log.e("tag",e.getMessage());
       }
       // dismiss the progress dialog   
       progressDialog.dismiss();
    }
}.start();

That is all!

回答3:

Progress Dialog doesn't show because you have to use a separated thread. The best practices in Android is to use AsyncTask ( highly recommended ). See also this answer.

回答4:

This is also possible by using AsyncTask. This class creates a thread for you. You should subclass it and fill in the doInBackground(...) method.