Introduction to Android Application Development, Fourth Edition (2014)

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Let’s look at a quick example of how you might implement a simple AlertDialog. In order to show an advantage of using the Fragment-based Dialog technique, we pass some data to the Dialog that demonstrates multiple instances of the DialogFragment class running within a singleActivity.

First, import the support version of the DialogFragment class (android.support.v4.app.DialogFragment) that is part of the Support Library. Then, just as before, you need to implement your own DialogFragment class. This class simply needs to be able to return an instance of the object that is fully configured and needs to implement the onCreateDialog method, which returns the fully configured AlertDialog, much as it did using the legacy method. The following code is a full implementation of a simple DialogFragment that manages an AlertDialog:

public class MyAlertDialogFragment extends DialogFragment {

public static MyAlertDialogFragment
newInstance(String fragmentNumber) {
MyAlertDialogFragment newInstance = new MyAlertDialogFragment();
Bundle args = new Bundle();
args.putString("fragnum", fragmentNumber);
newInstance.setArguments(args);
return newInstance;
}

@Override
public Dialog onCreateDialog(Bundle savedInstanceState) {
final String fragNum = getArguments().getString("fragnum");

AlertDialog.Builder alertDialog = new AlertDialog.Builder(
getActivity());
alertDialog.setTitle("Alert Dialog");
alertDialog.setMessage("This alert brought to you by "
+ fragNum );
alertDialog.setIcon(android.R.drawable.btn_star);
alertDialog.setPositiveButton(android.R.string.ok,
new DialogInterface.OnClickListener() {
@Override
public void onClick(DialogInterface dialog, int which) {
((SimpleFragDialogActivity) getActivity())
.doPositiveClick(fragNum);
return;
}
});
return alertDialog.create();
}
}

Now that you have defined your DialogFragment, you can use it within your Activity much as you would any Fragment—but this time, you must use the support version of the FragmentManager class, by calling the getSupportFragmentManager() method.

In your Activity, you need to import two support classes for this implementation to work: android.support.v4.app.DialogFragment and android.support.v4.app.FragmentActivity. Be sure to extend your Activity class from FragmentActivity, and not Activity as in the previous example, or your code will not work. The FragmentActivity class is a special class that makes fragments available with the Support Package.

The following FragmentActivity class, called SupportFragDialogActivity, has a layout resource that contains two Button controls, each of which triggers a new instance of the MyAlertDialogFragment to be generated and shown. The show() method of the DialogFragment is used to display theDialog, adding the Fragment to the support version of the FragmentManager, and passing in a little bit of information to configure the specific instance of the DialogFragment and its internal AlertDialog.

public class SupportFragDialogActivity extends FragmentActivity {
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);

// Handle Alert Dialog Button
Button launchAlertDialog = (Button) findViewById(
R.id.Button_AlertDialog);
launchAlertDialog.setOnClickListener(new View.OnClickListener() {
public void onClick(View v) {
String strFragmentNumber = "Fragment Instance One";
DialogFragment newFragment = MyAlertDialogFragment
.newInstance(strFragmentNumber);
showDialogFragment(newFragment, strFragmentNumber);
}
});

// Handle Alert Dialog 2 Button
Button launchAlertDialog2 = (Button) findViewById(
R.id.Button_AlertDialog2);
launchAlertDialog2.setOnClickListener(new View.OnClickListener() {
public void onClick(View v) {
String strFragmentNumber = "Fragment Instance Two";
DialogFragment newFragment = MyAlertDialogFragment
.newInstance(strFragmentNumber);
showDialogFragment(newFragment, strFragmentNumber);
}
});
}

void showDialogFragment(DialogFragment newFragment,
String strFragmentNumber) {
newFragment.show(getSupportFragmentManager(), strFragmentNumber);
}

public void doPositiveClick(String strFragmentNumber) {
Toast.makeText(getApplicationContext(),
"Clicked OK! (" + strFragmentNumber + ")",
Toast.LENGTH_SHORT).show();
}
}

Figure 10.3 shows a FragmentActivity using a DialogFragment to display a Dialog to the user with the Support Package.

Figure 10.3 Using DialogFragment instances in an Activity.

DialogFragment instances can be traditional pop-ups (as shown in the example provided) or they can be embedded like any other Fragment. Why might you want to embed a Dialog? Consider the following example: You’ve created a picture gallery application and implemented a customDialog that displays a larger image when you click a thumbnail. On small-screen devices, you might want this to be a pop-up Dialog, but on a tablet or TV, you might have the screen space to show the larger graphic off to the right or below the thumbnails. This would be a good opportunity to take advantage of code reuse and simply embed your Dialog.

Summary

Dialogs are useful controls for keeping your Android application user interfaces clean and user-friendly. Many types of Dialog controls are defined in the Android SDK, and you can create custom Dialog controls if none of the canned controls suit your purposes.

Developers should be aware that there are two different but similar approaches to implementing DialogFragment components within applications. The first approach is not backward compatible, but it does work well with devices that use Honeycomb and beyond. The second approach involves using a special type of DialogFragment and FragmentActivity. This method is backward compatible and provides the DialogFragment class for legacy applications that you may be maintaining.

Quiz Questions

1. What are the different types of dialogs available within the Android SDK?

2. True or false: When using a DialogFragment, you define the Dialog in the Activity onCreateDialog() method.

3. What is the method used to stop showing a Dialog?

4. What Dialog type should you use when creating a custom Dialog?

5. True or false: To display a backward-compatible DialogFragment, your Activity class must extend from the FragmentActivity Support Package class.

6. What is the method call for retrieving the FragmentManager when using the Support Package?

Exercises

1. Using the Android documentation, determine what interface classes the DialogFragment class implements.

2. Create an application that displays an AlertDialog and implement the DialogInterface.OnCancelListener to display a cancel message set with setCancelMessage, saying that the Dialog has been canceled when the user cancels the Dialog.

3. Create an application that is single-pane on small devices and two-pane on large devices. Implement a simple DialogFragment with text that displays as a Dialog on small devices, but on large devices, embed the Fragment into the right pane of the two-pane layout.

References and More Information

Android SDK Reference regarding the application Dialog class:

http://d.android.com/reference/android/app/Dialog.html

Android SDK Reference regarding the application AlertDialog class:

http://d.android.com/reference/android/app/AlertDialog.html

Android SDK Reference regarding the application DatePickerDialog class:

http://d.android.com/reference/android/app/DatePickerDialog.html

Android SDK Reference regarding the application TimePickerDialog class:

http://d.android.com/reference/android/app/TimePickerDialog.html

Android SDK Reference regarding the application ProgressDialog class:

http://d.android.com/reference/android/app/ProgressDialog.html

Android SDK Reference regarding the application CharacterPickerDialog class:

http://d.android.com/reference/android/text/method/CharacterPickerDialog.html

Android SDK Reference regarding the application DialogFragment class:

http://d.android.com/reference/android/app/DialogFragment.html

Android API Guides: “Dialogs”:

http://d.android.com/guide/topics/ui/dialogs.html

Android DialogFragment Reference: “Selecting Between Dialog or Embedding”:

http://d.android.com/reference/android/app/DialogFragment.html#DialogOrEmbed