LibGDX - 如何让我的按钮工作？

Question

我是LibGDX的新手，而且我慢慢服用。当我运行应用程序时，它只是因为错误而关闭。但我不确定问题是什么。这是我有的按钮的代码。

@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); 

} 

错误：

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.LwjglApplication$1.run(LwjglApplication.java:114) 

75行是显示（）方法是。

Answer 1

你的问题是，你的图片初始化之前，你正在使用图集初始化你的皮肤，图集是空指针。你做了：

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

当它应该是：

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