Android portrait and landscape layouts

Using the Application Class

Depending on what you're doing in your initialization you could consider creating a new class that extends Application and moving your initialization code into an overridden onCreate method within that class.

public class MyApplicationClass extends Application {
  @Override
  public void onCreate() {
    super.onCreate();
    // TODO Put your application initialization code here.
  }
}

The onCreate in the application class is only called when the entire application is created, so the Activity restarts on orientation or keyboard visibility changes won't trigger it.

It's good practice to expose the instance of this class as a singleton and exposing the application variables you're initializing using getters and setters.

NOTE: You'll need to specify the name of your new Application class in the manifest for it to be registered and used:

<application
    android:name="com.you.yourapp.MyApplicationClass"

Reacting to Configuration Changes [UPDATE: this is deprecated since API 13; see the recommended alternative]

As a further alternative, you can have your application listen for events that would cause a restart – like orientation and keyboard visibility changes – and handle them within your Activity.

Start by adding the android:configChanges node to your Activity's manifest node

 <activity android:name=".MyActivity"
      android:configChanges="orientation|keyboardHidden"
      android:label="@string/app_name">

or for Android 3.2 (API level 13) and newer:

<activity android:name=".MyActivity"
      android:configChanges="keyboardHidden|orientation|screenSize"
      android:label="@string/app_name">

Then within the Activity override the onConfigurationChanged method and call setContentView to force the GUI layout to be re-done in the new orientation.

@Override
public void onConfigurationChanged(Configuration newConfig) {
  super.onConfigurationChanged(newConfig);
  setContentView(R.layout.myLayout);
}

If you want the display dimensions in pixels you can use getSize:

Display display = getWindowManager().getDefaultDisplay();
Point size = new Point();
display.getSize(size);
int width = size.x;
int height = size.y;

If you're not in an Activity you can get the default Display via WINDOW_SERVICE:

WindowManager wm = (WindowManager) context.getSystemService(Context.WINDOW_SERVICE);
Display display = wm.getDefaultDisplay();

If you are in a fragment and want to acomplish this just use Activity.WindowManager (in Xamarin.Android) or getActivity().getWindowManager() (in java).

Before getSize was introduced (in API level 13), you could use the getWidth and getHeight methods that are now deprecated:

Display display = getWindowManager().getDefaultDisplay(); 
int width = display.getWidth();  // deprecated
int height = display.getHeight();  // deprecated

For the use case, you're describing, however, a margin/padding in the layout seems more appropriate.

Another way is: DisplayMetrics

A structure describing general information about a display, such as its size, density, and font scaling. To access the DisplayMetrics members, initialize an object like this:

DisplayMetrics metrics = new DisplayMetrics();
getWindowManager().getDefaultDisplay().getMetrics(metrics);

We can use widthPixels to get information for:

"The absolute width of the display in pixels."

Example:

Log.d("ApplicationTagName", "Display width in px is " + metrics.widthPixels);

API level 30 update

final WindowMetrics metrics = windowManager.getCurrentWindowMetrics();
 // Gets all excluding insets
 final WindowInsets windowInsets = metrics.getWindowInsets();
 Insets insets = windowInsets.getInsetsIgnoreVisibility(WindowInsets.Type.navigationBars()
         | WindowInsets.Type.displayCutout());

 int insetsWidth = insets.right + insets.left;
 int insetsHeight = insets.top + insets.bottom;

 // Legacy size that Display#getSize reports
 final Rect bounds = metrics.getBounds();
 final Size legacySize = new Size(bounds.width() - insetsWidth,
         bounds.height() - insetsHeight);