Intents

An activity often needs to start another activity at some point. This need arises, for instance, when an app needs to move from the current screen to a new one.

Depending on whether your activity wants a result back from the new activity it’s about to start, you start the new activity using either the startActivity() or the startActivityForResult() method. In either case, you pass in an Intent object.

The Intent object specifies either the exact activity you want to start or describes the type of action you want to perform (and the system selects the appropriate activity for you, which can even be from a different application). An Intent object can also carry small amounts of data to be used by the activity that is started.

startActivity():

  • If the newly started activity does not need to return a result

How to launch an activity called SignInActivity:

Intent intent = new Intent(this, SignInActivity.class);
startActivity(intent);

Your application might also want to perform some action, such as send an email, text message, or status update, using data from your activity. In this case, your application might not have its own activities to perform such actions, so you can instead leverage the activities provided by other applications on the device, which can perform the actions for you. For example, if you want to allow the user to send an email message, you can create the following intent:

Intent intent = new Intent(Intent.ACTION_SEND);
intent.putExtra(Intent.EXTRA_EMAIL, recipientArray);
startActivity(intent);

startActivityForResult():

Sometimes you want to get a result back from an activity when it ends. For example, you may start an activity that lets the user pick a person in a list of contacts; when it ends, it returns the person that was selected:

public class MyActivity extends Activity {
     // ...

     static final int PICK_CONTACT_REQUEST = 0;

     public boolean onKeyDown(int keyCode, KeyEvent event) {
         if (keyCode == KeyEvent.KEYCODE_DPAD_CENTER) {
             // When the user center presses, let them pick a contact.
             startActivityForResult(
                 new Intent(Intent.ACTION_PICK,
                 new Uri("content://contacts")),
                 PICK_CONTACT_REQUEST);
            return true;
         }
         return false;
     }

     protected void onActivityResult(int requestCode, int resultCode,
             Intent data) {
         if (requestCode == PICK_CONTACT_REQUEST) {
             if (resultCode == RESULT_OK) {
                 // A contact was picked.  Here we will just display it
                 // to the user.
                 startActivity(new Intent(Intent.ACTION_VIEW, data));
             }
         }
     }
 }