Question

点击ActionBar菜单选项后，我试图“转到”浮动contextMenu 。但我甚至无法加载应用程序，因为在启动之前我得到了一个例外。我正试图用这个简单的代码来做：

indexActivity.java

     protected void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);

            setContentView(R.layout.activity_index);
            registerForContextMenu(findViewById(R.id.action_share));
(...)

然后我有了

    public void onCreateContextMenu(ContextMenu menu, View v,
                                        ContextMenu.ContextMenuInfo menuInfo) {
            super.onCreateContextMenu(menu, v, menuInfo);
            menu.setHeaderTitle("Context Menu");
(...)

menu.xml文件：

<menu xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    tools:context=".IndexActivity">

    <item android:id="@+id/action_settings"
        android:title="@string/action_settings"
        android:orderInCategory="100"
        app:showAsAction="never" />

    <item android:id="@+id/action_share"
        android:title="@string/action_share"
        android:orderInCategory="100"
        app:showAsAction="never" />

但是我得到了Exception，我无法理解为什么因为我有 setContentView之前的findViewById(R.id.action_share). Can you please help me?

例外：

java.lang.RuntimeException: Unable to start activity ComponentInfo{com.converter.android.converter/com.converter.android.converter.IndexActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'int android.view.View.getId()' on a null object reference
            at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2298)
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2360)
            at android.app.ActivityThread.access$800(ActivityThread.java:144)
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1278)
            at android.os.Handler.dispatchMessage(Handler.java:102)
            at android.os.Looper.loop(Looper.java:135)
            at android.app.ActivityThread.main(ActivityThread.java:5221)
            at java.lang.reflect.Method.invoke(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:372)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:899)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694)
     Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'int android.view.View.getId()' on a null object reference
            at com.converter.android.converter.IndexActivity.onCreate(IndexActivity.java:33)
            at android.app.Activity.performCreate(Activity.java:5933)
            at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1105)
            at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2251)
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2360)
            at android.app.ActivityThread.access$800(ActivityThread.java:144)
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1278)
            at android.os.Handler.dispatchMessage(Handler.java:102)
            at android.os.Looper.loop(Looper.java:135)

Android：创建ContextMenu时出现异常

0 个答案: