关于setContentView

位置

调用setContentView()要写在组件代码前, onCreate()方法后.

public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main); 
         ... ... //组件代码
}

否则会抛出如下NPE

08-03 19:23:15.200: ERROR/InputDispatcher(69): channel '407ecfe8 com.example.helloandroid/com.example.helloandroid.HelloAndroid (server)' ~ Consumer closed input channel or an error occurred.  events=0x8
08-03 19:23:15.200: ERROR/InputDispatcher(69): channel '407ecfe8 com.example.helloandroid/com.example.helloandroid.HelloAndroid (server)' ~ Channel is unrecoverably broken and will be disposed!
08-03 19:23:21.910: ERROR/AndroidRuntime(444): FATAL EXCEPTION: main
08-03 19:23:21.910: ERROR/AndroidRuntime(444): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.helloandroid/com.example.helloandroid.HelloAndroid}: java.lang.NullPointerException
08-03 19:23:21.910: ERROR/AndroidRuntime(444):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1647)
08-03 19:23:21.910: ERROR/AndroidRuntime(444):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1663)
08-03 19:23:21.910: ERROR/AndroidRuntime(444):     at android.app.ActivityThread.access$1500(ActivityThread.java:117)
08-03 19:23:21.910: ERROR/AndroidRuntime(444):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:931)
08-03 19:23:21.910: ERROR/AndroidRuntime(444):     at android.os.Handler.dispatchMessage(Handler.java:99)
08-03 19:23:21.910: ERROR/AndroidRuntime(444):     at android.os.Looper.loop(Looper.java:123)
08-03 19:23:21.910: ERROR/AndroidRuntime(444):     at android.app.ActivityThread.main(ActivityThread.java:3683)
08-03 19:23:21.910: ERROR/AndroidRuntime(444):     at java.lang.reflect.Method.invokeNative(Native Method)
08-03 19:23:21.910: ERROR/AndroidRuntime(444):     at java.lang.reflect.Method.invoke(Method.java:507)
08-03 19:23:21.910: ERROR/AndroidRuntime(444):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:839)
08-03 19:23:21.910: ERROR/AndroidRuntime(444):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:597)
08-03 19:23:21.910: ERROR/AndroidRuntime(444):     at dalvik.system.NativeStart.main(Native Method)
08-03 19:23:21.910: ERROR/AndroidRuntime(444): Caused by: java.lang.NullPointerException
08-03 19:23:21.910: ERROR/AndroidRuntime(444):     at com.example.helloandroid.HelloAndroid.onCreate(HelloAndroid.java:19)
08-03 19:23:21.910: ERROR/AndroidRuntime(444):     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047)
08-03 19:23:21.910: ERROR/AndroidRuntime(444):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1611)
08-03 19:23:21.910: ERROR/AndroidRuntime(444):     ... 11 more


参数

setContentView中指向R.layout的静态变量, 这个静态变量main代表layout文件夹下的main.xml. 以此类推, 每增加一个新的activity, 都要为这个activity指定一个新的layout,也就是设置新的View. 如果不同activity都指向同一个R.layout.main,运行会失败, 没有log信息.

评论

1 楼 追求幸福 2011-12-30  

每增加一个新的activity, 都要为这个activity指定一个新的layout,也就是设置新的View. 如果不同activity都指向同一个R.layout.main,运行会失败, 没有log信息。--->请问楼主这是什么意思？