java - Android虚拟设备中的 'Unfortunately Testapp has stopped'错误消息

Question

我是 Android 应用程序开发新手，我尝试编写我的第一个简单应用程序来尝试在 Activity 之间发送数据。代码已编译，我尝试在虚拟设备上启动它，但正如标题所示，它停止了。

这是 logcat 输出:

     08-16 22:44:22.729: D/AndroidRuntime(800): Shutting down VM
     08-16 22:44:22.749: W/dalvikvm(800): threadid=1: thread exiting with uncaught exception          (group=0x414c4700)
     08-16 22:44:22.829: E/AndroidRuntime(800): FATAL EXCEPTION: main
     08-16 22:44:22.829: E/AndroidRuntime(800): java.lang.RuntimeException: Unable to    instantiate activity ComponentInfo{com.example.Testapp/com.example.Testapp.FirstActivity}:   java.lang.NullPointerException
     08-16 22:44:22.829: E/AndroidRuntime(800):     at    android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2137)
     08-16 22:44:22.829: E/AndroidRuntime(800):     at  android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2261)
     08-16 22:44:22.829: E/AndroidRuntime(800):     at android.app.ActivityThread.access$600(ActivityThread.java:141)
     08-16 22:44:22.829: E/AndroidRuntime(800):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1256)
     08-16 22:44:22.829: E/AndroidRuntime(800):     at android.os.Handler.dispatchMessage(Handler.java:99)
     08-16 22:44:22.829: E/AndroidRuntime(800):     at android.os.Looper.loop(Looper.java:137)
     08-16 22:44:22.829: E/AndroidRuntime(800):     at andr     oid.app.ActivityThread.main(ActivityThread.java:5103)
     08-16 22:44:22.829: E/AndroidRuntime(800):     at java.lang.reflect.Method.invokeNative(Native Method)
     08-16 22:44:22.829: E/AndroidRuntime(800):     at  java.lang.reflect.Method.invoke(Method.java:525)
     08-16 22:44:22.829: E/AndroidRuntime(800):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:737)
     08-16 22:44:22.829: E/AndroidRuntime(800):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
      08-16 22:44:22.829: E/AndroidRuntime(800):    at dalvik.system.NativeStart.main(Native Method)
      08-16 22:44:22.829: E/AndroidRuntime(800): Caused by: java.lang.NullPointerException
      08-16 22:44:22.829: E/AndroidRuntime(800):    at     android.app.Activity.findViewById(Activity.java:1853)
     08-16 22:44:22.829: E/AndroidRuntime(800):     at com.example.Testapp.FirstActivity.<init>(FirstActivity.java:12)
     08-16 22:44:22.829: E/AndroidRuntime(800):     at java.lang.Class.newInstanceImpl(Native Method)
     08-16 22:44:22.829: E/AndroidRuntime(800):     at java.lang.Class.newInstance(Class.java:1130)
     08-16 22:44:22.829: E/AndroidRuntime(800):     at android.app.Instrumentation.newActivity(Instrumentation.java:1061)
08-16 22:44:22.829: E/AndroidRuntime(800):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2128)
08-16 22:44:22.829: E/AndroidRuntime(800):  ... 11 more
08-16 22:45:14.220: I/Process(800): Sending signal. PID: 800 SIG: 9
08-16 22:45:29.609: D/AndroidRuntime(903): Shutting down VM
08-16 22:45:29.619: W/dalvikvm(903): threadid=1: thread exiting with uncaught exception (group=0x414c4700)
08-16 22:45:29.679: E/AndroidRuntime(903): FATAL EXCEPTION: main
08-16 22:45:29.679: E/AndroidRuntime(903): java.lang.RuntimeException: Unable to instantiate     activity ComponentInfo{com.example.Testapp/com.example.Testapp.FirstActivity}: java.lang.NullPointerException
08-16 22:45:29.679: E/AndroidRuntime(903):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2137)
08-16 22:45:29.679: E/AndroidRuntime(903):  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2261)
08-16 22:45:29.679: E/AndroidRuntime(903):  at android.app.ActivityThread.access$600(ActivityThread.java:141)
08-16 22:45:29.679: E/AndroidRuntime(903):  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1256)
08-16 22:45:29.679: E/AndroidRuntime(903):  at android.os.Handler.dispatchMessage(Handler.java:99)
08-16 22:45:29.679: E/AndroidRuntime(903):  at android.os.Looper.loop(Looper.java:137)
08-16 22:45:29.679: E/AndroidRuntime(903):  at android.app.ActivityThread.main(ActivityThread.java:5103)
08-16 22:45:29.679: E/AndroidRuntime(903):  at java.lang.reflect.Method.invokeNative(Native Method)
08-16 22:45:29.679: E/AndroidRuntime(903):  at     java.lang.reflect.Method.invoke(Method.java:525)
08-16 22:45:29.679: E/AndroidRuntime(903):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:737)
08-16 22:45:29.679: E/AndroidRuntime(903):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
08-16 22:45:29.679: E/AndroidRuntime(903):  at dalvik.system.NativeStart.main(Native Method)
08-16 22:45:29.679: E/AndroidRuntime(903): Caused by: java.lang.NullPointerException
08-16 22:45:29.679: E/AndroidRuntime(903):  at android.app.Activity.findViewById(Activity.java:1853)
08-16 22:45:29.679: E/AndroidRuntime(903):  at com.example.Testapp.FirstActivity.<init>(FirstActivity.java:12)
08-16 22:45:29.679: E/AndroidRuntime(903):  at java.lang.Class.newInstanceImpl(Native Method)
08-16 22:45:29.679: E/AndroidRuntime(903):  at java.lang.Class.newInstance(Class.java:1130)
08-16 22:45:29.679: E/AndroidRuntime(903):  at android.app.Instrumentation.newActivity(Instrumentation.java:1061)
08-16 22:45:29.679: E/AndroidRuntime(903):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2128)
08-16 22:45:29.679: E/AndroidRuntime(903):  ... 11 more

任何人都可以告诉，这个日志引用了什么错误以及我应该在哪里寻找来解决这个问题。

祝一切顺利

Answer 1

Can anybody tell, what error this log references and where I should look for to fix this issue.

第一行，后面有异常(exception)

FATAL EXCEPTION: main
 08-16 22:44:22.829: E/AndroidRuntime(800): java.lang.RuntimeException: Unable to    instantiate activity ComponentInfo{com.example.Testapp/com.example.Testapp.FirstActivity}:   java.lang.NullPointerException

Caused by: java.lang.NullPointerException

告诉我们有一个NPE。然后，如果我们找到引用您的项目的第一行，它将告诉我们行号

at com.example.Testapp.FirstActivity.<init>(FirstActivity.java:12)

在 FirstActivity 第 12 行，有东西是 null。最有可能在膨胀布局之前实例化View，但可以是任何东西。

如果您无法弄清楚什么/为什么某些内容为 null，请发布第 12 行周围的行。