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我想（从 Activity 继承）通过第二个类访问 ImageView 并更改它。不幸的是，当我尝试这样做时，我得到了 NullPointerExeption。第二个类没有 XML，也没有 onCreate() 方法。它继承自 Activity 只是因为我需要一些功能。

那么如何访问布局或其他组件呢？

这是我第二堂课的代码。

public void changeLoerg() {
    int stufe;
    //layout = (RelativeLayout)findViewById(R.id.LayoutMain);
    imageViewLoerg = (ImageView)findViewById(R.id.imageViewLoerg);

    stufe = SettingsLoerg.getLevel(context);

    Object tag = imageViewLoerg.getTag();

    if (stufe == 1) {
        int loergId = R.drawable.animatedegg;

        if( tag != null && ((Integer)tag).intValue() == loergId) {
            loergId = R.drawable.animatedloerg;
            animatedLoerg.stop();
            //playAnimationNodelay();
            imageViewLoerg.setTag(loergId);
            imageViewLoerg.setBackgroundResource(loergId);
            playAnimationNodelay();
        }
    }
}

在 hier das LogCat 下：

01-05 21:34:39.685: W/dalvikvm(9905): threadid=1: thread exiting with uncaught exception (group=0x41b5b300)
01-05 21:34:39.693: E/AndroidRuntime(9905): FATAL EXCEPTION: main
01-05 21:34:39.693: E/AndroidRuntime(9905): java.lang.NullPointerException
01-05 21:34:39.693: E/AndroidRuntime(9905):     at android.app.Activity.findViewById(Activity.java:1825)
01-05 21:34:39.693: E/AndroidRuntime(9905):     at at.android.dertestloerk.TimerLoerg.changeLoerg(TimerLoerg.java:42)
01-05 21:34:39.693: E/AndroidRuntime(9905):     at at.android.dertestloerk.TimerLoerg$1.run(TimerLoerg.java:100)
01-05 21:34:39.693: E/AndroidRuntime(9905):     at android.os.Handler.handleCallback(Handler.java:615)
01-05 21:34:39.693: E/AndroidRuntime(9905):     at android.os.Handler.dispatchMessage(Handler.java:92)
01-05 21:34:39.693: E/AndroidRuntime(9905):     at android.os.Looper.loop(Looper.java:137)
01-05 21:34:39.693: E/AndroidRuntime(9905):     at android.app.ActivityThread.main(ActivityThread.java:4745)
01-05 21:34:39.693: E/AndroidRuntime(9905):     at java.lang.reflect.Method.invokeNative(Native Method)
01-05 21:34:39.693: E/AndroidRuntime(9905):     at java.lang.reflect.Method.invoke(Method.java:511)
01-05 21:34:39.693: E/AndroidRuntime(9905):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:786)
01-05 21:34:39.693: E/AndroidRuntime(9905):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
01-05 21:34:39.693: E/AndroidRuntime(9905):     at dalvik.system.NativeStart.main(Native Method)
4

1 回答 1

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如果您有一个View要修改的类，您应该在该类中创建一个方法来修改所说View的 . 然后你可以调用你的方法Activity并传入你需要的任何参数作为参数。

public class BackGround { // please don't extend Activity unless it is one

    private ImageView img;

    ....

    public void changeLoerg(int resourceId) {
        img.setBackgroundResource(resourceId);      
    }
}
于 2013-01-06T00:06:23.620 回答