java - 将 ShareActionProvider 与 Android 支持库结合使用时出现 NullPointerException

Question

我按照 Google 的指示执行了这封信 ( http://developer.android.com/guide/topics/ui/actionbar.html#ActionProvider )，但我无法让它发挥作用。我正在尝试在操作栏添加一个共享按钮。这是我的代码:

MyActivity.java

import android.support.v4.view.MenuItemCompat;
import android.support.v7.widget.ShareActionProvider;

private ShareActionProvider mShareActionProvider;

@Override
public boolean onCreateOptionsMenu(Menu menu) {
    getMenuInflater().inflate(R.menu.my_activity, menu);

    MenuItem menuItem = menu.findItem(R.id.menu_item_share);
    mShareActionProvider = (ShareActionProvider) MenuItemCompat.getActionProvider(menuItem);

    Intent intent = new Intent(Intent.ACTION_SEND);
    intent.setType("image/png");
    intent.putExtra(Intent.EXTRA_STREAM, Uri.parse(FILE_PATH));
    mShareActionProvider.setShareIntent(intent);    // Line 52

    return super.onCreateOptionsMenu(menu);
}

my_activity.xml

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

    <item android:id="@+id/menu_item_share"
        android:title="@string/share"
        android:icon="@drawable/social_share"
        android:orderInCategory="100"
        app:showAsAction="always"
        app:actionProviderClass="android.support.v7.widget.ShareActionProvider" />

</menu>

LogCat 说:

java.lang.NullPointerException
        at it.mrhyde.example.activity.MyActivity.onCreateOptionsMenu(MyActivity.java:52)
        at android.app.Activity.onCreatePanelMenu(Activity.java:2449)
        at com.android.internal.policy.impl.PhoneWindow.preparePanel(PhoneWindow.java:405)
        at com.android.internal.policy.impl.PhoneWindow.invalidatePanelMenu(PhoneWindow.java:756)
        at com.android.internal.policy.impl.PhoneWindow$1.run(PhoneWindow.java:2852)
        at android.os.Handler.handleCallback(Handler.java:605)
        at android.os.Handler.dispatchMessage(Handler.java:92)
        at android.os.Looper.loop(Looper.java:137)
        at android.app.ActivityThread.main(ActivityThread.java:4424)
        at java.lang.reflect.Method.invokeNative(Native Method)
        at java.lang.reflect.Method.invoke(Method.java:511)
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:817)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:584)
        at dalvik.system.NativeStart.main(Native Method)

我做错了什么？!

Answer 1

确保您的 Activity 扩展了 ActionBarActivity(而不仅仅是 Activity)。它必须这样 MenuItemCompat.getActionProvider(menuItem); 可以返回正确的值。