Understanding how ProgressDialog works

Question

I work with a Device with fix API 23 and because I thought it would be easy I wanted to use ProgressDialog since it is still available.

I tried to start a Thread which needs to do a lot of work and while he is doing this the user has to wait.

I got different issues while using the ProgressDialog:

1. Doesn't stop

public void buttun(View view) {

        ProgressDialog mProgressDialog = new ProgressDialog(this);
        mProgressDialog.show(this,"Title","Message",true);
        addCustomQueue.start();
        getCustomQueue.start();
        mProgressDialog.dismiss();
}

In this case with the button click the ProgressDialog shows up but .dismiss() doesn't work. (I know that the ProgessDialog should close immediately even when the Thread is not finished. I just wanted to know if .dismiss() works.)

2. To much work on MainThread

public void buttun(View view) {

        ProgressDialog mProgressDialog = new ProgressDialog(this);
        mProgressDialog.show(this,"Title","Message",true);
        addCustomQueue.start();
        getCustomQueue.start();

        try {
            addCustomQueue.join();
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        mProgressDialog.dismiss();
    }

When I try to .join() one Thread which will surely end after 20 sec, the ProgressDialog shows up after about 30s and also .dismiss() doesn't work. But I got the information about the thread being finished.

The Style I want to use is the second one, but I need a proper way to do it. What is the right way to use this?

Answer 1

1. Doesn't stop

In fact, ProgressDialog.show(Context, String, String, boolean) is a static method, it creates a new ProgressDialog and return it after showing it.

You should change your code like this.

ProgressDialog mProgressDialog = ProgressDialog.show(this,"Title","Message",true);
mProgressDialog.dismiss();

2. Too much work on MainThread

You should never block Android's MainThread, so join a thread on MainThread is not a good idea.

Instead of joining a long-running thread on MainThread, you can use a Handler to post callbacks on MainThread.

Your Activity:

public class MainActivity extends AppCompatActivity {

    private ProgressDialog mProgressDialog;
    private AddCustomQueueThread addCustomQueue;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        addCustomQueue = new AddCustomQueueThread(this);
    }

    public void dismissProgressDialog() {
        if(mProgressDialog != null) {
            mProgressDialog.dismiss();
            mProgressDialog = null;
        }
    }

    @Override
    protected void onDestroy() {
        super.onDestroy();
        if(mProgressDialog != null) {
            mProgressDialog.dismiss();
            mProgressDialog = null;
        }
    }

    public void button(View view) {
        addCustomQueue.start();
        mProgressDialog = ProgressDialog.show(this,"Title","Message",true);
    }
}

Your Thread:

    class AddCustomQueueThread extends Thread {
        final WeakReference<MainActivity> activity;
        final Handler handler;
        AddCustomQueueThread(MainActivity act) {
            activity = new WeakReference<>(act);
            handler = new Handler(Looper.getMainLooper());
        }

        @Override
        public void run() {
            super.run();

            //do your work.

            handler.post(new Runnable() {
                @Override
                public void run() {
                    MainActivity act = activity.get();
                    if(act != null) {
                        act.dismissProgressDialog();
                    }
                }
            });

        }
    }

Please note: we are storing reference to activity inside a WeakReference, this is needed to prevent leaking of your activity.