How to display progress dialog before starting an activity in Android?

How do you display a progress dialog before starting an activity (i.e., while the activity is loading some data) in Andro开发者_运维百科id?

You should load data in an AsyncTask and update your interface when the data finishes loading.

You could even start a new activity in your AsyncTask's onPostExecute() method.

More specifically, you will need a new class that extends AsyncTask:

public class MyTask extends AsyncTask<Void, Void, Void> {
  public MyTask(ProgressDialog progress) {
    this.progress = progress;
  }

  public void onPreExecute() {
    progress.show();
  }

  public void doInBackground(Void... unused) {
    ... do your loading here ...
  }

  public void onPostExecute(Void unused) {
    progress.dismiss();
  }
}

Then in your activity you would do:

ProgressDialog progress = new ProgressDialog(this);
progress.setMessage("Loading...");
new MyTask(progress).execute();

When you start a long-running process on Android, its always advisable to do it on another thread. You can then use the UI thread to display a progress dialog. You cannot display a progress dialog in the same (UI) thread in which the process is running.

Do the following to start your process

pd = ProgressDialog.show(this, "Synchronizing data", "Please wait...");
Thread t = new Thread(this);
t.start();

For this your activity should implement Runnable as follows

public class SyncDataActivity extends Activity implements Runnable

And finally a method to perform the long-running process

@Override
public void run() {
      //your code here
}