我遵循this tutorial,并在这段代码中的DisplayMessageActivity的onCreate方法中获得了一个NullPointerException:
if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.HONEYCOMB) {
// Show the Up button in the action bar.
getActionBar().setDisplayHomeAsUpEnabled(true); //Exception here
}
我在一个仿真器上运行应用程序,遵循NexusOne AVD模板。
当我单击send按钮并输入一些文本时,我得到了一个异常。
日志如下:
09-03 23:02:07.586: E/AndroidRuntime(7095): FATAL EXCEPTION: main
09-03 23:02:07.586: E/AndroidRuntime(7095): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.mypackage.myfirstapp/com.mypackage.myfirstapp.DisplayMessageActivity}: java.lang.NullPointerException
09-03 23:02:07.586: E/AndroidRuntime(7095): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2180)
09-03 23:02:07.586: E/AndroidRuntime(7095): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2230)
09-03 23:02:07.586: E/AndroidRuntime(7095): at android.app.ActivityThread.access$600(ActivityThread.java:141)
09-03 23:02:07.586: E/AndroidRuntime(7095): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1234)
09-03 23:02:07.586: E/AndroidRuntime(7095): at android.os.Handler.dispatchMessage(Handler.java:99)
09-03 23:02:07.586: E/AndroidRuntime(7095): at android.os.Looper.loop(Looper.java:137)
09-03 23:02:07.586: E/AndroidRuntime(7095): at android.app.ActivityThread.main(ActivityThread.java:5041)
09-03 23:02:07.586: E/AndroidRuntime(7095): at java.lang.reflect.Method.invokeNative(Native Method)
09-03 23:02:07.586: E/AndroidRuntime(7095): at java.lang.reflect.Method.invoke(Method.java:511)
09-03 23:02:07.586: E/AndroidRuntime(7095): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793)
09-03 23:02:07.586: E/AndroidRuntime(7095): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560)
09-03 23:02:07.586: E/AndroidRuntime(7095): at dalvik.system.NativeStart.main(Native Method)
09-03 23:02:07.586: E/AndroidRuntime(7095): Caused by: java.lang.NullPointerException
09-03 23:02:07.586: E/AndroidRuntime(7095): at com.mypackage.myfirstapp.DisplayMessageActivity.onCreate(DisplayMessageActivity.java:40)
09-03 23:02:07.586: E/AndroidRuntime(7095): at android.app.Activity.performCreate(Activity.java:5104)
09-03 23:02:07.586: E/AndroidRuntime(7095): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1080)
09-03 23:02:07.586: E/AndroidRuntime(7095): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2144)
09-03 23:02:07.586: E/AndroidRuntime(7095): ... 11 more
通过对此块进行注释,应用程序可以成功运行。
为什么抛出NullPointerException?
https://stackoverflow.com/questions/18602953
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