TimePicker点击改变时间时java.lang.NullPointerException异常

07-23 16:41:58.568: W/System.err(19676): java.lang.NullPointerException

07-23 16:41:58.577: W/System.err(19676): at android.widget.TimePicker.updateInputState(TimePicker.java:580)

07-23 16:41:58.579: W/System.err(19676): at android.widget.TimePicker.access$000(TimePicker.java:56)

07-23 16:41:58.583: W/System.err(19676): at android.widget.TimePicker$2.onValueChange(TimePicker.java:150)

07-23 16:41:58.586: W/System.err(19676): at android.widget.NumberPicker.notifyChange(NumberPicker.java:1795)

07-23 16:41:58.588: W/System.err(19676): at android.widget.NumberPicker.setValueInternal(NumberPicker.java:1581)

07-23 16:41:58.591: W/System.err(19676): at android.widget.NumberPicker.changeValueByOne(NumberPicker.java:1611)

07-23 16:41:58.593: W/System.err(19676): at android.widget.NumberPicker.access$200(NumberPicker.java:90)

07-23 16:41:58.595: W/System.err(19676): at android.widget.NumberPicker$1.onClick(NumberPicker.java:633)

07-23 16:41:58.598: W/System.err(19676): at android.view.View.performClick(View.java:4254)

07-23 16:41:58.602: W/System.err(19676): at android.view.View$PerformClick.run(View.java:17728)

07-23 16:41:58.604: W/System.err(19676): at android.os.Handler.handleCallback(Handler.java:800)

07-23 16:41:58.607: W/System.err(19676): at android.os.Handler.dispatchMessage(Handler.java:100)

07-23 16:41:58.610: W/System.err(19676): at android.os.Looper.loop(Looper.java:194)

07-23 16:41:58.613: W/System.err(19676): at android.app.ActivityThread.main(ActivityThread.java:5463)

07-23 16:41:58.616: W/System.err(19676): at java.lang.reflect.Method.invokeNative(Native Method)

07-23 16:41:58.619: W/System.err(19676): at java.lang.reflect.Method.invoke(Method.java:525)

07-23 16:41:58.620: W/System.err(19676): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:854)

07-23 16:41:58.622: W/System.err(19676): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:621)

07-23 16:41:58.624: W/System.err(19676): at dalvik.system.NativeStart.main(Native Method)

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解决方法：

<TimePicker

android:id="@+id/alarmclock_time"

android:layout_width="wrap_content"

android:layout_height="wrap_content"

android:layout_gravity="center_horizontal" />

<requestFocus />

在TimerPicker控件后面加上<requestFocus />就行了

原理不明，知道的请告诉我。谢谢