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

android:configChanges="keyboardHidden|orientation"

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

android:configChanges="keyboardHidden|orientation|screenSize"

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);
}

Read More

You need to modify AndroidManifest.xml as Intrications (previously Ashton) mentioned and make sure the activity handles the onConfigurationChanged event as you want it handled. This is how it should look:

@Override
public void onConfigurationChanged(Configuration newConfig) {
    super.onConfigurationChanged(newConfig);
    setRequestedOrientation(ActivityInfo.SCREEN_ORIENTATION_PORTRAIT);
}

Read More

You've got to handle configuration changes yourself.

http://developer.android.com/guide/topics/resources/runtime-changes.html#HandlingTheChange

Sample:

// from the link above
@Override
public void onConfigurationChanged(Configuration newConfig) {
    super.onConfigurationChanged(newConfig);


    // Checks whether a hardware keyboard is available
    if (newConfig.hardKeyboardHidden == Configuration.HARDKEYBOARDHIDDEN_NO) {
        Toast.makeText(this, "keyboard visible", Toast.LENGTH_SHORT).show();
    } else if (newConfig.hardKeyboardHidden == Configuration.HARDKEYBOARDHIDDEN_YES) {
        Toast.makeText(this, "keyboard hidden", Toast.LENGTH_SHORT).show();
    }
}

Then just change the visibility of some views, update a field, and change your layout file.

Note

This solution will not work for soft keyboards and onConfigurationChanged will not be called for soft keyboards.

Read More

I was able to narrow down the problem to the onMeasure function in the VideoView class. By creating a child class and overriding the onMeasure function, I was able to get the desired functionality.

public class VideoViewCustom extends VideoView {

    private int mForceHeight = 0;
    private int mForceWidth = 0;
    public VideoViewCustom(Context context) {
        super(context);
    }

    public VideoViewCustom(Context context, AttributeSet attrs) {
        this(context, attrs, 0);
    }

    public VideoViewCustom(Context context, AttributeSet attrs, int defStyle) {
        super(context, attrs, defStyle);
    }

    public void setDimensions(int w, int h) {
        this.mForceHeight = h;
        this.mForceWidth = w;

    }

    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        Log.i("@@@@", "onMeasure");

        setMeasuredDimension(mForceWidth, mForceHeight);
    }
}

Then inside my Activity I just did the following:

@Override
public void onConfigurationChanged(Configuration newConfig) {
    super.onConfigurationChanged(newConfig);

    if (newConfig.orientation == Configuration.ORIENTATION_LANDSCAPE) {
        getWindow().clearFlags(WindowManager.LayoutParams.FLAG_FORCE_NOT_FULLSCREEN);
        getWindow().setFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN, WindowManager.LayoutParams.FLAG_FULLSCREEN);

        questionVideo.setDimensions(displayHeight, displayWidth);
        questionVideo.getHolder().setFixedSize(displayHeight, displayWidth);

    } else {
        getWindow().setFlags(WindowManager.LayoutParams.FLAG_FORCE_NOT_FULLSCREEN, WindowManager.LayoutParams.FLAG_FORCE_NOT_FULLSCREEN);

        questionVideo.setDimensions(displayWidth, smallHeight);
        questionVideo.getHolder().setFixedSize(displayWidth, smallHeight);

    }
}

The line:

questionVideo.getHolder().setFixedSize(displayWidth, smallHeight);

is key in order to make this work. If you do the setDimensions call without this guy, the video still will not resize.

The only other thing you need to do is ensure that you call setDimensions() inside the onCreate() method as well or your video will not start buffering as the video won't be set to draw on a surface of any size.

// onCreate()
questionVideo.setDimensions(initialWidth, initialHeight); 

One last key part - if you ever find yourself wondering why the VideoView isn't resizing on rotation, you need to ensure the dimensions you're resizing to are either exactly equal to the visible area or less than it. I had a really big problem where I was setting the VideoView's width/height to the entire display size when I still had the notification bar/title bar on the screen and it was not resizing the VideoView at all. Simply removing the notification bar and title bar fixed the problem.

Hopefully this helps someone in the future!

EDIT: (June 2016)

This answer is very old (I think android 2.2/2.3) and probably is not as relevant as the other answers below! Look to them first unless you're dev-ing on legacy Android :)

Read More

what I did...

in the manifest, to the activity section, added:

android:configChanges="keyboardHidden|orientation"

in the code for the activity, implemented:

//used in onCreate() and onConfigurationChanged() to set up the UI elements
public void InitializeUI()
{
    //get views from ID's
    this.textViewHeaderMainMessage = (TextView) this.findViewById(R.id.TextViewHeaderMainMessage);

    //etc... hook up click listeners, whatever you need from the Views
}

//Called when the activity is first created.
@Override
public void onCreate(Bundle savedInstanceState)
{
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main);

    InitializeUI();
}

//this is called when the screen rotates.
// (onCreate is no longer called when screen rotates due to manifest, see: android:configChanges)
@Override
public void onConfigurationChanged(Configuration newConfig)
{
    super.onConfigurationChanged(newConfig);
    setContentView(R.layout.main);

    InitializeUI();
}

Read More