fragment.onCreateView 导致空指针异常

Posted 2023-02-19

【中文标题】fragment.onCreateView 导致空指针异常

【英文标题】：fragment.onCreateView causes null pointer exception

【发布时间】：2014-04-02 07:23:49

【问题描述】：

所以我正在使用片段并尝试在它们上连接点击侦听器。

public View onCreateView(LayoutInflater inflater, ViewGroup container,
            Bundle savedInstanceState) 
        View contentView = inflater.inflate(R.layout.layout1, null);
      //  View contentView=super.onCreateView(inflater,null,savedInstanceState,R.layout.layout1);
        startButton= (Button) getView().findViewById(R.id.button);

这是按钮的 XML

 <Button
            android:layout_
            android:layout_
            android:text="Start Time"
            android:id="@+id/button"
            android:layout_alignParentLeft="true"
            android:layout_marginLeft="28dp"
            android:layout_marginTop="10dp"
            android:background="#1e497c"
            android:textColor="#ffffff"/>

这是我的例外

02-28 16:49:57.162 14375-14375/com.example.listviewandroid E/AndroidRuntime: 致命

EXCEPTION: main
    java.lang.RuntimeException: Unable to start activity ComponentInfocom.example.listviewandroid/com.example.listviewandroid.MainActivity: java.lang.NullPointerException
            at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2245)
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2295)
            at android.app.ActivityThread.access$700(ActivityThread.java:150)
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1280)
            at android.os.Handler.dispatchMessage(Handler.java:99)
            at android.os.Looper.loop(Looper.java:175)
            at android.app.ActivityThread.main(ActivityThread.java:5279)
            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:1102)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:869)
            at dalvik.system.NativeStart.main(Native Method)
     Caused by: java.lang.NullPointerException
            at com.example.fragment.Fragment1.onCreateView(Fragment1.java:43)
            at android.support.v4.app.Fragment.performCreateView(Fragment.java:1478)
            at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:927)
            at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1104)
            at android.support.v4.app.BackStackRecord.run(BackStackRecord.java:682)
            at android.support.v4.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1460)
            at android.support.v4.app.FragmentActivity.onStart(FragmentActivity.java:556)
            at android.app.Instrumentation.callActivityOnStart(Instrumentation.java:1181)
            at android.app.Activity.performStart(Activity.java:5293)
            at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2218)
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2295)
            at android.app.ActivityThread.access$700(ActivityThread.java:150)
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1280)
            at android.os.Handler.dispatchMessage(Handler.java:99)
            at android.os.Looper.loop(Looper.java:175)
            at android.app.ActivityThread.main(ActivityThread.java:5279)
            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:1102)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:869)
            at dalvik.system.NativeStart.main(Native Method)

很明显它无法找到按钮或发生了我无法弄清楚的事情。非常感谢任何帮助。

【参考方案1】：

只需在您的 onCreateView 中使用它

    View contentView = inflater.inflate(R.layout.layout1, container, false);
    startButton= (Button) contentView.findViewById(R.id.button);
    return contentView;

【参考方案2】：

在onCreateView() 返回之前，您不能使用getView()，因为它是负责创建所述视图的方法。您应该将代码更改为

public View onCreateView(LayoutInflater inflater, ViewGroup container,
            Bundle savedInstanceState) 
        View contentView = inflater.inflate(R.layout.layout1, null);
        startButton = (Button) contentView.findViewById(R.id.button);

或者，覆盖onViewCreated() 并在该方法中实现您的按钮设置（使用getView()。

【参考方案3】：

这行没有意义：

startButton= (Button) getView().findViewById(R.id.button);

您还没有视图，您仍在创建它..

相反，您可以这样做：

 startButton= (Button)contentView.findViewById(R.id.button);

或者等到 onCreateView 方法返回你刚刚创建的实际视图，然后你就可以在 onCreateView 返回视图后使用“getView”方法获取视图的引用了..

希望对你有帮助！

问候！