LibGDX - How do I get my button to work?

Question

I'm new to LibGDX and I am taking it slowly. When I run the application it just force closes due to an error. But I'm not sure what the problem is. Here is the code for the button that I have.

@Override
public void show() {
 // Viewport Camera
 camera = new PerspectiveCamera();
 viewport = new ExtendViewport(800, 480, camera);
 stage = new Stage(new ExtendViewport(800, 840));
 Gdx.input.setInputProcessor(stage);
 skin = new Skin(atlas);
 atlas = new TextureAtlas(Gdx.files.internal("ui/button.pack"));
 table = new Table(skin);
 table.setBounds(0, 0, Gdx.graphics.getWidth(), Gdx.graphics.getHeight());
 textButtonStyle = new TextButtonStyle();
 textButtonStyle.up = skin.getDrawable("button.up");
 textButtonStyle.down = skin.getDrawable("button.down");
 buttonPlay = new TextButton("Play", textButtonStyle);
 buttonPlay.setWidth((float) (Gdx.graphics.getWidth()/2.5));
 buttonPlay.setHeight(Gdx.graphics.getHeight()/6);
 buttonPlay.setPosition((Gdx.graphics.getWidth()/2-buttonPlay.getWidth()/2), (float) (Gdx.graphics.getHeight()-(buttonPlay.getHeight())*2.5));
 buttonPlay.toFront();
 stage.addActor(buttonPlay);
 table.debug();
 table.add(buttonPlay);
}

The error:

Exception in thread "LWJGL Application" java.lang.NullPointerException
at com.badlogic.gdx.scenes.scene2d.ui.Skin.addRegions(Skin.java:102)
at com.badlogic.gdx.scenes.scene2d.ui.Skin.<init>(Skin.java:88)
at com.badlogic.gdx.screens.Menu.show(Menu.java:83)
at com.badlogic.gdx.Game.setScreen(Game.java:61)
at com.badlogic.gdx.screens.Splash.render(Splash.java:38)
at com.badlogic.gdx.Game.render(Game.java:46)
at com.dakotapederson.slingshotsteve.SlingshotSteve.render(SlingshotSteve.java:29)
at com.badlogic.gdx.backends.lwjgl.LwjglApplication.mainLoop(LwjglApplication.java:206)
at com.badlogic.gdx.backends.lwjgl.LwjglApplication1ドル.run(LwjglApplication.java:114)

Line 75 is where the show() method is.

• Veljko: What is the error? Provide log please.
• Dakota: Their you go, I update the code with a table to see if that would fix things

Answer 1

Your problem is that you are initialising your skin with an atlas before your atlas has been initialised, the atlas is the null pointer. You have done:

skin = new Skin(atlas); //Here atlas isn't loaded so exception occurs
atlas = new TextureAtlas(Gdx.files.internal("ui/button.pack"));

When it should be:

atlas = new TextureAtlas(Gdx.files.internal("ui/button.pack")); // Load atlas first
skin = new Skin(atlas);

• Dakota: Thanks, it fixed that problem, but then I get a "Missing LabelStyleFont Error". What do I do about that?
• Basim Khajwal: The problem you are getting is probably because your uiskin atlas doesn't have a style for the label you are making, the one your are loading from "ui/button.pack" sounds like it only has a UI for a button. You can read more about UI skins at:github.com/libgdx/libgdx/wiki/Skin. If you want a full pre-made UI atlas you can download one here: stackoverflow.com/questions/16182844/default-skin-libgdx