java - 我在启动 libgdx 游戏时遇到 java.lang.ExceptionInInitializerError

Question

我正在尝试在 Android Studio (0.8.14) 中使用 libgdx 开发一个简单的 2D 游戏，但此时(只有一个启动画面和一个空菜单)我遇到了一个错误，这个 LogCat 输出，当我启动该应用程序时(我正在 Sony Xperia Z1 设备上进行测试):

12-02 18:01:52.146  24248-24248/com.ak.thesoccerball.android D/dalvikvm﹕ Late-enabling CheckJNI
12-02 18:01:52.196  24248-24248/com.ak.thesoccerball.android W/ActivityThread﹕ Application com.ak.thesoccerball.android can be debugged on port 8100...
12-02 18:01:52.246  24248-24248/com.ak.thesoccerball.android D/dalvikvm﹕ Trying to load lib /data/app-lib/com.ak.thesoccerball.android-1/libgdx.so 0x447c06f0
12-02 18:01:52.246  24248-24248/com.ak.thesoccerball.android D/dalvikvm﹕ Added shared lib /data/app-lib/com.ak.thesoccerball.android-1/libgdx.so 0x447c06f0
12-02 18:01:52.246  24248-24248/com.ak.thesoccerball.android D/dalvikvm﹕ No JNI_OnLoad found in /data/app-lib/com.ak.thesoccerball.android-1/libgdx.so 0x447c06f0, skipping init
12-02 18:01:52.246  24248-24248/com.ak.thesoccerball.android W/dalvikvm﹕ Exception Ljava/lang/NullPointerException; thrown while initializing Lcom/ak/thesoccerball/AKGame;
12-02 18:01:52.246  24248-24248/com.ak.thesoccerball.android D/AndroidRuntime﹕ Shutting down VM
12-02 18:01:52.246  24248-24248/com.ak.thesoccerball.android W/dalvikvm﹕ threadid=1: thread exiting with uncaught exception (group=0x41618d88)
12-02 18:01:52.256  24248-24248/com.ak.thesoccerball.android E/AndroidRuntime﹕ FATAL EXCEPTION: main
    Process: com.ak.thesoccerball.android, PID: 24248
    java.lang.ExceptionInInitializerError
            at com.ak.thesoccerball.android.AndroidLauncher.onCreate(AndroidLauncher.java:17)
            at android.app.Activity.performCreate(Activity.java:5231)
            at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087)
            at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2201)
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2286)
            at android.app.ActivityThread.access$800(ActivityThread.java:144)
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1246)
            at android.os.Handler.dispatchMessage(Handler.java:102)
            at android.os.Looper.loop(Looper.java:212)
            at android.app.ActivityThread.main(ActivityThread.java:5135)
            at java.lang.reflect.Method.invokeNative(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:515)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:877)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:693)
            at dalvik.system.NativeStart.main(Native Method)
     Caused by: java.lang.NullPointerException
            at com.ak.thesoccerball.AKGame.<clinit>(AKGame.java:9)
            at com.ak.thesoccerball.android.AndroidLauncher.onCreate(AndroidLauncher.java:17)
            at android.app.Activity.performCreate(Activity.java:5231)
            at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087)
            at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2201)
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2286)
            at android.app.ActivityThread.access$800(ActivityThread.java:144)
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1246)
            at android.os.Handler.dispatchMessage(Handler.java:102)
            at android.os.Looper.loop(Looper.java:212)
            at android.app.ActivityThread.main(ActivityThread.java:5135)
            at java.lang.reflect.Method.invokeNative(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:515)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:877)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:693)
            at dalvik.system.NativeStart.main(Native Method)

涉及的类如下: - AndroidLauncher.java

package com.ak.thesoccerball.android;

import android.os.Bundle;

import com.badlogic.gdx.backends.android.AndroidApplication;
import com.badlogic.gdx.backends.android.AndroidApplicationConfiguration;

import com.ak.thesoccerball.AKGame;

public class AndroidLauncher extends AndroidApplication {
    @Override
    protected void onCreate (Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        AndroidApplicationConfiguration config = new AndroidApplicationConfiguration();
        config.useAccelerometer = false;
        config.useCompass = false;
        initialize(new AKGame(), config);
    }
}

AKGame.java

package com.ak.thesoccerball;

import com.badlogic.gdx.Game;
import com.badlogic.gdx.Gdx;
import com.badlogic.gdx.graphics.g2d.SpriteBatch;

public class AKGame extends Game {

    public static final int WIDTH = Gdx.graphics.getWidth();
    public static final int HEIGHT = Gdx.graphics.getHeight();

    public SpriteBatch batch;

    @Override
    public void create() {
        batch = new SpriteBatch();
        setScreen(new SplashScreen(this));
    }

    public void render() {
        super.render(); //important!
    }

    public void dispose() {
        batch.dispose();
    }


}

这是 AndroidManifest.xml:

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.ak.thesoccerball.android"
    android:versionCode="1"
    android:versionName="1.0" >

    <uses-sdk android:minSdkVersion="8" android:targetSdkVersion="21" />

    <uses-feature android:glEsVersion="0x00020000" android:required="true" />

    <application
        android:allowBackup="true"
        android:icon="@drawable/ic_launcher"
        android:label="@string/app_name"
        android:theme="@style/GdxTheme" >
        <activity
            android:name="com.ak.thesoccerball.android.AndroidLauncher"
            android:label="@string/app_name" 
            android:screenOrientation="portrait"
            android:configChanges="keyboard|keyboardHidden|orientation|screenSize">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />
                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
    </application>

</manifest>

我错过了什么？

Answer 1

移动这段代码:

public static final int WIDTH = Gdx.graphics.getWidth(); 
public static final int HEIGHT = Gdx.graphics.getHeight();

进入create()方法，例如:

@Override
public void create() {
     WIDTH = Gdx.graphics.getWidth(); 
     HEIGHT = Gdx.graphics.getHeight();
     //..
}

问题是，在调用 create 方法之前，Gdx 仍然为 null，无法使用。