Showing a Dialog Fullscreen or as an Embedded Fragment

You might have a UI design in which you want a piece of the UI to appear as a dialog in some situations, but as a full screen or embedded fragment in others (perhaps depending on whether the device is a large screen or small screen). The DialogFragment class offers you this flexibility because it can still behave as an embeddable Fragment.

However, you cannot use AlertDialog.Builder or other Dialog objects to build the dialog in this case. If you want the DialogFragment to be embeddable, you must define the dialog's UI in a layout, then load the layout in the onCreateView() callback.

Here's an example DialogFragment that can appear as either a dialog or an embeddable fragment (using a layout named purchase_items.xml):

public class CustomDialogFragment extends DialogFragment {
    /** The system calls this to get the DialogFragment's layout, regardless
        of whether it's being displayed as a dialog or an embedded fragment. */
    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
            Bundle savedInstanceState) {
        // Inflate the layout to use as dialog or embedded fragment
        return inflater.inflate(R.layout.purchase_items, container, false);
    }

    /** The system calls this only when creating the layout in a dialog. */
    @Override
    public Dialog onCreateDialog(Bundle savedInstanceState) {
        // The only reason you might override this method when using onCreateView() is
        // to modify any dialog characteristics. For example, the dialog includes a
        // title by default, but your custom layout might not need it. So here you can
        // remove the dialog title, but you must call the superclass to get the Dialog.
        Dialog dialog = super.onCreateDialog(savedInstanceState);
        dialog.requestWindowFeature(Window.FEATURE_NO_TITLE);
        return dialog;
    }
}

And here's some code that decides whether to show the fragment as a dialog or a fullscreen UI, based on the screen size:

public void showDialog() {
    FragmentManager fragmentManager = getSupportFragmentManager();
    CustomDialogFragment newFragment = new CustomDialogFragment();

    if (mIsLargeLayout) {
        // The device is using a large layout, so show the fragment as a dialog
        newFragment.show(fragmentManager, "dialog");
    } else {
        // The device is smaller, so show the fragment fullscreen
        FragmentTransaction transaction = fragmentManager.beginTransaction();
        // For a little polish, specify a transition animation
        transaction.setTransition(FragmentTransaction.TRANSIT_FRAGMENT_OPEN);
        // To make it fullscreen, use the 'content' root view as the container
        // for the fragment, which is always the root view for the activity
        transaction.add(android.R.id.content, newFragment)
                   .addToBackStack(null).commit();
    }
}

For more information about performing fragment transactions, see the Fragments guide.

In this example, the mIsLargeLayout boolean specifies whether the current device should use the app's large layout design (and thus show this fragment as a dialog, rather than fullscreen). The best way to set this kind of boolean is to declare a bool resource value with an alternative resourcevalue for different screen sizes. For example, here are two versions of the bool resource for different screen sizes:

res/values/bools.xml

<!-- Default boolean values -->
<resources>
    <bool name="large_layout">false</bool>
</resources>

res/values-large/bools.xml

<!-- Large screen boolean values -->
<resources>
    <bool name="large_layout">true</bool>
</resources>

Then you can initialize the mIsLargeLayout value during the activity's onCreate() method:

boolean mIsLargeLayout;

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    mIsLargeLayout = getResources().getBoolean(R.bool.large_layout);
}

Showing an activity as a dialog on large screens

Instead of showing a dialog as a fullscreen UI when on small screens, you can accomplish the same result by showing an Activity as a dialog when on large screens. Which approach you choose depends on your app design, but showing an activity as a dialog is often useful when your app is already designed for small screens and you'd like to improve the experience on tablets by showing a short-lived activity as a dialog.

To show an activity as a dialog only when on large screens, apply the Theme.Holo.DialogWhenLarge theme to the <activity> manifest element:

<activity android:theme="@android:style/Theme.Holo.DialogWhenLarge" >

For more information about styling your activities with themes, see the Styles and Themes guide.

From: https://developer.android.com/guide/topics/ui/dialogs.html#FullscreenDialog