Question

我有一个非常基本的活动，有一个Android的ImageView：id =“@ + id / imageViewTest” 然后在OnCreate方法中调用：

ImageView imageView =  (ImageView)findViewById(R.id.imageViewTest);
    // Set the background color to white
    imageView.setBackgroundColor(Color.WHITE);

这给出了错误：

    10-15 16:36:27.552  29097-29097/org.explore.self.beginner D/dalvikvm﹕ Late-enabling CheckJNI
10-15 16:36:28.017  29097-29097/org.explore.self.beginner D/AndroidRuntime﹕ Shutting down VM
10-15 16:36:28.017  29097-29097/org.explore.self.beginner W/dalvikvm﹕ threadid=1: thread exiting with uncaught exception (group=0x41d9b2a0)
10-15 16:36:28.042  29097-29097/org.explore.self.beginner E/AndroidRuntime﹕ FATAL EXCEPTION: main
    java.lang.RuntimeException: Unable to start activity ComponentInfo{org.explore.self.beginner/org.selfexplore.android.view.activity.TestActivity}: java.lang.NullPointerException
            at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2110)
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2135)
            at android.app.ActivityThread.access$700(ActivityThread.java:140)
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1237)
            at android.os.Handler.dispatchMessage(Handler.java:99)
            at android.os.Looper.loop(Looper.java:137)
            at android.app.ActivityThread.main(ActivityThread.java:4921)
            at java.lang.reflect.Method.invokeNative(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:511)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1038)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:805)
            at dalvik.system.NativeStart.main(Native Method)
     Caused by: java.lang.NullPointerException
            at org.selfexplore.android.view.activity.TestActivity.onCreate(TestActivity.java:37)
            at android.app.Activity.performCreate(Activity.java:5188)
            at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1094)
            at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2074)
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2135)
            at android.app.ActivityThread.access$700(ActivityThread.java:140)
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1237)
            at android.os.Handler.dispatchMessage(Handler.java:99)
            at android.os.Looper.loop(Looper.java:137)
            at android.app.ActivityThread.main(ActivityThread.java:4921)
            at java.lang.reflect.Method.invokeNative(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:511)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1038)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:805)
            at dalvik.system.NativeStart.main(Native Method)
10-15 16:36:28.062  29097-29097/org.explore.self.beginner I/Process﹕ Sending signal. PID: 29097 SIG: 9

但是当我做了

ImageView imageView = new ImageView(this);

它运作正常，为什么？

PS：我无法在此处添加布局代码，因此请在此文档中分享：https://docs.google.com/document/d/1fbi3B_hAYUh_C2IwPfInvZ-BG2bgsa4pZoJKj8NBT9o/edit?usp=sharing

Answer 1

您使用setContentView()设置的布局没有ID imageViewTest和findViewById()返回null的视图，或者您没有调用{{1}完全没有。

在ImageView上的findViewById为什么setBackgroundColor给出NullPointerException

1 个答案: