libgdx - why extend Game instead of implement ApplicationListener?

heisenbergman · May 5, 2013, 12:06pm

Was reading this article: Using Screen and Game Classes and I was wondering why a lot of tutorials I come across use “extends Game” instead of “implements ApplicationListener”?

Currently, my main class for the game I’m trying to make implements ApplicationListener.

I was hoping to understand “extends Game” more so that I could decide which is better.

Thanks!

davedes · May 5, 2013, 12:37pm

If you want multiple states (i.e. menu, gameplay, options, etc) then you can utilize LibGDX’s “Game” and “Screen” helper classes. They are very minimal, and it’s easy enough to write your own state management if you’d rather do something specific (i.e. fancy transitions between states). Game is just an extension of ApplicationListener.

Look at how simple the Game and Screen classes are to get an idea of what they do.

github.com

libgdx/libgdx/blob/master/gdx/src/com/badlogic/gdx/Screen.java

/*******************************************************************************
 * Copyright 2011 See AUTHORS file.
 * 
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 * 
 *   http://www.apache.org/licenses/LICENSE-2.0
 * 
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 ******************************************************************************/

package com.badlogic.gdx;

/** <p>
 * Represents one of many application screens, such as a main menu, a settings menu, the game screen and so on.

This file has been truncated. show original

github.com

libgdx/libgdx/blob/master/gdx/src/com/badlogic/gdx/Game.java

/*******************************************************************************
 * Copyright 2011 See AUTHORS file.
 * 
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 * 
 *   http://www.apache.org/licenses/LICENSE-2.0
 * 
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 ******************************************************************************/

package com.badlogic.gdx;

/** <p>
 * An {@link ApplicationListener} that delegates to a {@link Screen}. This allows an application to easily have multiple screens.

This file has been truncated. show original

JavaGameXYZ · May 6, 2013, 4:56pm

I struggled with this question too. I ultimately worked through Andrew Steigert’s blog series on building a Tyrion clone and it helped me a lot.

Like davedes says, it’s mainly so you can support multiple screens, where each screen contains its own code (e.g. render(float delta))