Android sdk : java. lang.NullPointerException: 尝试调用虚拟方法

Question

当我尝试在我的设备上调试应用程序并试图在几个小时内摆脱它时我遇到了这个错误......并且无法弄清楚......如果有人能找到解决方案那就太棒了因为我想尽快发布我的应用程序的新更新..

07-05 22:45:02.550    2821-2821/davvarn.csgo_maps E/AndroidRuntime﹕ FATAL EXCEPTION: main
    Process: davvarn.csgo_maps, PID: 2821
    java.lang.RuntimeException: Unable to start activity ComponentInfo{davvarn.csgo_maps/davvarn.csgo_maps.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.ImageView.setImageDrawable(android.graphics.drawable.Drawable)' on a null object reference
            at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2356)
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2418)
            at android.app.ActivityThread.access$900(ActivityThread.java:154)
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1321)
            at android.os.Handler.dispatchMessage(Handler.java:102)
            at android.os.Looper.loop(Looper.java:135)
            at android.app.ActivityThread.main(ActivityThread.java:5289)
            at java.lang.reflect.Method.invoke(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:372)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:904)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:699)
     Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.ImageView.setImageDrawable(android.graphics.drawable.Drawable)' on a null object reference
            at davvarn.csgo_maps.MainActivity.changeContent(MainActivity.java:176)
            at davvarn.csgo_maps.MainActivity.onCreate(MainActivity.java:115)
            at android.app.Activity.performCreate(Activity.java:5990)
            at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1106)
            at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2309)
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2418)
            at android.app.ActivityThread.access$900(ActivityThread.java:154)
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1321)
            at android.os.Handler.dispatchMessage(Handler.java:102)
            at android.os.Looper.loop(Looper.java:135)
            at android.app.ActivityThread.main(ActivityThread.java:5289)
            at java.lang.reflect.Method.invoke(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:372)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:904)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:699)

我真的不知道如何将 MainActivity 文件粘贴到这里，因为我是 Stackoverflow 的新手。请告诉我怎么做，我会尝试一下。

Answer 1

确保您已经初始化了 ImageView 并使用了在 XML 中定义的正确 ID。您可以像这样初始化 ImageView:

ImageView imageView = (ImageView)findViewById(R.id.yourImageViewIDHere);

让您在 onCreate 调用 setContentView 后执行此操作。