使用支持库共享操作提供程序时出现空指针异常

Question

下面是我的 Activity 的代码。在此我使用支持库 appcompat

   import android.content.Intent;
   import android.os.Bundle;
   import  android.support.v4.view.MenuItemCompat;
   import android.support.v7.app.ActionBarActivity;
   import android.support.v7.widget.ShareActionProvider;
   import android.view.Menu;
   import android.view.MenuItem;

  public class MainActivity extends ActionBarActivity {


@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
}

@Override
public boolean onCreateOptionsMenu(Menu menu) {
    // Inflate the menu; this adds items to the action bar if it is present.
    getMenuInflater().inflate(R.menu.activity_main, menu);
    MenuItem item = (MenuItem) menu.findItem(R.id.share_options);
    ShareActionProvider shareAction = (ShareActionProvider) MenuItemCompat
            .getActionProvider(item);
    Intent shareIntent = new Intent(Intent.ACTION_SEND)
            .setAction(Intent.ACTION_SEND)
            .putExtra(Intent.EXTRA_TEXT, "MobiTexter")
            .setType("text/plain");
    shareAction.setShareIntent(shareIntent);
    return super.onCreateOptionsMenu(menu);
}

}

以下是我的菜单选项 XML 文件，它是一个 ShareActionProvider 小部件

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

<item
    android:id="@+id/share_options"
    android:actionProviderClass="android.support.v7.widget.ShareActionProvider"
    android:orderInCategory="100"
    mobitexter:showAsAction="never"
    mobitexter:title="@string/share_options"/>

  </menu>

在这我得到一个 NullPointerException 。以下是我的日志猫输出。

          10-02 12:49:00.813: E/AndroidRuntime(9227): FATAL EXCEPTION: main
          10-02 12:49:00.813: E/AndroidRuntime(9227): java.lang.NullPointerException
          10-02 12:49:00.813: E/AndroidRuntime(9227):   at net.mobitexter.easyshare.MainActivity.onCreateOptionsMenu(MainActivity.java:31)
          10-02 12:49:00.813: E/AndroidRuntime(9227):   at android.app.Activity.onCreatePanelMenu(Activity.java:2444)
          10-02 12:49:00.813: E/AndroidRuntime(9227):   at android.support.v4.app.FragmentActivity.onCreatePanelMenu(FragmentActivity.java:224)
          10-02 12:49:00.813: E/AndroidRuntime(9227):   at android.support.v7.app.ActionBarActivity.superOnCreatePanelMenu(ActionBarActivity.java:224)
          10-02 12:49:00.813: E/AndroidRuntime(9227):   at android.support.v7.app.ActionBarActivityDelegateICS.onCreatePanelMenu(ActionBarActivityDelegateICS.java:141)
          10-02 12:49:00.813: E/AndroidRuntime(9227):   at android.support.v7.app.ActionBarActivity.onCreatePanelMenu(ActionBarActivity.java:199)
          10-02 12:49:00.813: E/AndroidRuntime(9227):   at  android.support.v7.app.ActionBarActivityDelegateICS$WindowCallbackWrapper.onCreatePanelMenu(ActionBarActivityDelegateICS.java:280)
          10-02 12:49:00.813: E/AndroidRuntime(9227):   at com.android.internal.policy.impl.PhoneWindow.preparePanel(PhoneWindow.java:392)
          10-02 12:49:00.813: E/AndroidRuntime(9227):   at com.android.internal.policy.impl.PhoneWindow.invalidatePanelMenu(PhoneWindow.java:743)
          10-02 12:49:00.813: E/AndroidRuntime(9227):   at com.android.internal.policy.impl.PhoneWindow$1.run(PhoneWindow.java:2838)
          10-02 12:49:00.813: E/AndroidRuntime(9227):   at android.os.Handler.handleCallback(Handler.java:605)
          10-02 12:49:00.813: E/AndroidRuntime(9227):   at android.os.Handler.dispatchMessage(Handler.java:92)
          10-02 12:49:00.813: E/AndroidRuntime(9227):   at android.os.Looper.loop(Looper.java:137)
          10-02 12:49:00.813: E/AndroidRuntime(9227):   at android.app.ActivityThread.main(ActivityThread.java:4448)
          10-02 12:49:00.813: E/AndroidRuntime(9227):   at java.lang.reflect.Method.invokeNative(Native Method)
          10-02 12:49:00.813: E/AndroidRuntime(9227):   at java.lang.reflect.Method.invoke(Method.java:511)
          10-02 12:49:00.813: E/AndroidRuntime(9227):   at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:823)
          10-02 12:49:00.813: E/AndroidRuntime(9227):   at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:590)
          10-02 12:49:00.813: E/AndroidRuntime(9227):   at dalvik.system.NativeStart.main(Native Method)

Answer 1

我发现了错误。问题是支持库需要自定义前缀而不是 android:actionProviderClass 。我做错了什么，我使用android:actionProviderClass 而不是customprefix:actionProviderClass

请看这里：https://developer.android.com/training/basics/actionbar/adding-buttons.html

Answer 2

如果这一行

shareAction.setShareIntent(shareIntent);

正在抛出一个NullPointerException，这句话

(ShareActionProvider) MenuItemCompat.getActionProvider(item);

必须返回null。

看看下面的帖子，其中谈到了发生这种情况的原因。

NullPointerException on setShareIntent using ActionBarSherlock

Answer 3

我改了

android:actionProviderClass=widget.ShareActionProvider" />

到这里

app:actionProviderClass=support.v7.widget.ShareActionProvider" />