So, in the last part we created some parts of the UI the user sees when he starts the game.

Today we want to create a small part of the real “Game View”!
First, lets change the standard layout of the Android App. The layout file can be found in res/layout/main.xml.
The standard is a simple LinearLayout with a TextView, that currently just displays “Hello…” when you start the game.
Let’s remove this part and change it to:

<?xml version="1.0" encoding="utf-8"?>
<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    >
 
    <GameView
    	android:id="@+id/game"
    	android:layout_width="fill_parent"
    	android:layout_height="fill_parent" />
 
    <RelativeLayout
	android:layout_width="fill_parent"
	android:layout_height="fill_parent">
	<TextView
		android:id="@+id/text"
		android:text="@string/space_janitor_info_text"
		android:visibility="visible"
		android:layout_height="wrap_content"
		android:layout_width="wrap_content"
		android:layout_centerInParent="true"
		android:gravity="center_horizontal"
		android:textColor="#88ffffff"
		android:textSize="24sp" />
    </RelativeLayout>
</FrameLayout>

First, we define a Game View that we can use later on to hold the game graphics. Second we defined a RelativeLayout that holds a TextView, we need this to display some infos later on.

Now let’s extend the code to use this views.

Create a new class called GameView in your App. The GameView extends SurfaceView and has to implement the SufaceHolder.Callback interface. Add the yet unimplemented methods and a constructor to fulfill the interface’s requirements.

public class GameView extends SurfaceView implements SurfaceHolder.Callback {
 
	public GameView(Context context, AttributeSet attrs) {
		super(context, attrs);
		// TODO Auto-generated constructor stub
	}
 
	public void surfaceChanged(SurfaceHolder holder, int format, int width,
			int height) {
		// TODO Auto-generated method stub
 
	}
 
	public void surfaceCreated(SurfaceHolder holder) {
		// TODO Auto-generated method stub
 
	}
 
	public void surfaceDestroyed(SurfaceHolder holder) {
		// TODO Auto-generated method stub
 
	}
}

The SurfaceView is designated to hold the game graphics. Via the SurfaceHolder.Callback we are informed about dimension changes, i.e. when the user switches to landscape mode.

In the Main View we now have to code a connection to the Game View, we’ll do this via an instance variable of GameView. Add a variable of the type “GameView” to your Activity.

public class SpaceJanitor extends Activity {
	private static final int MENU_START = 1;
	private GameView myGameView;
        ...
}

In our “onCreate”-method we have to initialize this variable and we would like to give the GameView the ability to display some info in the TextView we recently defined in our layout file, like “Game Over”, etc. So:

public void onCreate(Bundle savedInstanceState) {
   super.onCreate(savedInstanceState);
 
   requestWindowFeature(Window.FEATURE_NO_TITLE);
   setContentView(R.layout.main);
   myGameView = (GameView) findViewById(R.id.game);
   myGameView.setTextView = (TextView) findViewById(R.id.text);
}

This implies that we have to add a method “setTextView” in the GameView class to save a reference on this TextView locally.

public void setTextView(TextView findViewById) {
		// TODO Auto-generated method stub	
	}

In the next part we will add a thread to handle graphic updates, user actions, etc. etc.

First I have to say that I am using Eclipse and the Android plugin to program, because it really minifies the work needed. If your using another IDE you have to change some of the steps according to your IDE’s workflow, but the code stays the same.

I decided that my game should have a welcome screen and an options menu to start the game (or later when playing to pause or stop the game). That is easily done with Android.
First lets create a new project in Android, name it what you like, I chose “Space Janitor” (I assume that you already now how to create new Android project, otherwise refer to one of the many tutorials).

You will then see something like this:

 
package de.rakery.android.spacejanitor.part1;
 
import android.app.Activity;
import android.os.Bundle;
 
public class SpaceJanitor extends Activity {
    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
    }
}

We want to use the full screen for our game and don’t need the window title, so add the following to the onCreate Method:

requestWindowFeature(Window.FEATURE_NO_TITLE);

Press Cmd-Shift-O in Eclipse (sorry, only have a Mac, don’t know which keys on Win/Linux) to automatically import the needed dependencies (here android.view.Window).

Next, lets create the Options Menu to start the game.
We don’t want to keep the Text-Strings in our code, so lets move them to the XML file in res/values/strings.xml.
When using Eclipse you will be presented with the following screen after double-clicking the file:

So, now you can easily add a new string key-value pair. Add a key “MENU_FIRST” and as value “Start new game” to the strings.xml.
We will later add more menu items, but this one is enough for now.

So how do we add this String as a Menu item to the options menu?
On Android when an activity starts a method onCreateOptionsMenu is called automatically at some points. So we can override the normal method of the class Activity and add our own onCreateOptionsMenu-method.
Lets do this by adding the following right under the onCreate Method

@Override
public boolean onCreateOptionsMenu(Menu menu){
	super.onCreateOptionsMenu(menu);
        menu.add(0, MENU_START, 0, R.string.MENU_FIRST);
	return true;
}

The add-Method takes 4 arguments: the groupId, the itemId, the order, and a title.
As you can see, we set the title by reading R.string.MENU_FIRST (the key we used for the text-string).
I also defined a

private static final int MENU_START = 1;

for my activity, that is now set as the menu itemId, which can later be used to identify user clicks on a menu item.
I’ve set the group ID to 0 because currently there is only one group with the ID zero, and I want to order the items in the order I add them to the menu, so I can set order to 0. If you would like to order in a different way you would have to set the order explicitly.

Now we also want to react on user clicks on a menu item. Once again we override a method defined in Activity called onOptionsItemsSelect:

public boolean onOptionsItemsSelect(MenuItem item){
        switch (item.getItemId()){
	   	// do something with the clicks
	   	case MENU_START:
		// TODO: Define what to do on click
	 }
	 return true;
}

Here we can make use of the constant MENU_START we defined to compare it to the itemID.

Start the emulator and you will see a black screen with a text “Hello World, Space Janitor”. When clicking on the options button, the menu will show up and display the Menuitem “Start new game”.

So, this was part one of the game development on Android tutorial, not much game development here, but we have to start somewhere

So I decided to write a simple game for the Android platform, not that there aren’t already enough games in the Android Market, more because in the last weeks I mostly concentrated on developing games for the Vodafone mobile widget runtime. I made a game called “Space Janitor”, which I now want to port to the Android platform. I would like to extend the game at some points, i.e. making use of the device accelerometer sensors to move the spaceship to the left or to the right, or vibrating the mobile when being hit by an asteroid. That would be real fun.

Another good way to learn is to try to explain the things one learned to others. That was a great way to learn during my university time, because the professors always wanted to have something explained So if one already explained the learned things to others, it was no problem to explain it again to the professor. I now decided to keep track of my development by writing some blog posts about how to develop the game, thus explaing it to others. But I would also very much appreciate your comments on how to improve the quality and the speed of my code as I would call myself just a novice in Android programming. Maybe you’ve also got some more tipps for game improvement, game handling, gameplay, etc.

I will somewhat unregularly post new entries in my blog, so keep in touch.

Mal schauen wann es in Deutschland zu haben ist.

Mit einem Klick auf die übertragene Datei wird dann der Widget Manager von Vodafone (falls noch nicht auf dem Handy, dann hier runterladen) und das Spiel gestartet.

Geflogen wird mit den Tasten 2, 4, 6 und 8 für vorne, links, rechts und runter, und das Ziel des Spieles ist möglichst viele Satelliten einzusammeln ohne von den Asteroiden getroffen zu werden.

Viel Spaß beim Müllsammeln!

Update:
11.06.09: Habe soeben erfahren, dass Space Janitor schon 460mal von der Vodafone Plattform heruntergeladen wurde. Wer’s jetzt noch nicht hat, sofort holen!

Viel Spaß beim Zocken!