Java Android FragmentActivity中OnCreateOptions菜单中的NullPointerException

这里是detailActivity.java，它从openWeatherAPI收集数据并将数据填充到listView中。当我单击listView上的项目时，OnCreateOptions菜单中有NPE

package com.example.sunshine2;

import android.content.Intent;
import android.database.Cursor;
import android.os.Bundle;

import android.support.v4.app.Fragment;

import android.support.v4.app.LoaderManager.LoaderCallbacks;
import android.support.v4.content.CursorLoader;
import android.support.v4.content.Loader;

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

import android.util.Log;
import android.view.LayoutInflater;
import android.view.Menu;
import android.view.MenuInflater;
import android.view.MenuItem;
import android.view.View;
import android.view.ViewGroup;
import android.widget.TextView;

import com.example.sunshine2.data.WeatherContract.WeatherEntry;

public class DetailActivity extends ActionBarActivity {

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_detail);
    if (savedInstanceState == null) {
        getSupportFragmentManager().beginTransaction()
                .add(R.id.container, new DetailFragment()).commit();
    }
}

@Override
public boolean onCreateOptionsMenu(Menu menu) {
    // Inflate the menu; this adds items to the action bar if it is present.
    getMenuInflater().inflate(R.menu.detail, menu);
    return true;
}

@Override
public boolean onOptionsItemSelected(MenuItem item) {
    // Handle action bar item clicks here. The action bar will
    // automatically handle clicks on the Home/Up button, so long
    // as you specify a parent activity in AndroidManifest.xml.
    int id = item.getItemId();
    if (id == R.id.action_settings) {
        startActivity(new Intent(this, SettingsActivity.class));
        return true;
    }
    return super.onOptionsItemSelected(item);
}

/**
 * A placeholder fragment containing a simple view.
 */
public static class DetailFragment extends Fragment implements
        LoaderCallbacks<Cursor> {

    private static final String LOG_TAG = DetailFragment.class
            .getSimpleName();

    private static final String FORECAST_SHARE_HASHTAG = " #SunshineApp";

    private ShareActionProvider mShareActionProvider;
    private String mForecast;

    private static final int DETAIL_LOADER = 0;

    private static final String[] FORECAST_COLUMNS = {
            WeatherEntry.TABLE_NAME + "." + WeatherEntry._ID,
            WeatherEntry.COLUMN_DATE, WeatherEntry.COLUMN_SHORT_DESC,
            WeatherEntry.COLUMN_MAX_TEMP, WeatherEntry.COLUMN_MIN_TEMP, };

    // these constants correspond to the projection defined above, and must
    // change if the
    // projection changes
    private static final int COL_WEATHER_ID = 0;
    private static final int COL_WEATHER_DATE = 1;
    private static final int COL_WEATHER_DESC = 2;
    private static final int COL_WEATHER_MAX_TEMP = 3;
    private static final int COL_WEATHER_MIN_TEMP = 4;

    public DetailFragment() {
        setHasOptionsMenu(true);
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
            Bundle savedInstanceState) {
        return inflater.inflate(R.layout.fragment_detail, container, false);
    }

    @Override
    public void onCreateOptionsMenu(Menu menu, MenuInflater inflater) {
        // Inflate the menu; this adds items to the action bar if it is
        // present.
        inflater.inflate(R.menu.detail_fragment, menu);

        // Retrieve the share menu item
        MenuItem menuItem = menu.findItem(R.id.action_share);

        // Get the provider and hold onto it to set/change the share intent.
        mShareActionProvider = (ShareActionProvider) MenuItemCompat
                .getActionProvider(menuItem);

        // If onLoadFinished happens before this, we can go ahead and set
        // the share intent now.
        if (mForecast != null) {
            mShareActionProvider
                    .setShareIntent(createShareForecastIntent());
        }
    }

    private Intent createShareForecastIntent() {
        Intent shareIntent = new Intent(Intent.ACTION_SEND);
        shareIntent.addFlags(Intent.FLAG_ACTIVITY_CLEAR_WHEN_TASK_RESET);
        shareIntent.setType("text/plain");
        shareIntent.putExtra(Intent.EXTRA_TEXT, mForecast
                + FORECAST_SHARE_HASHTAG);
        return shareIntent;
    }

    @Override
    public void onActivityCreated(Bundle savedInstanceState) {
        getLoaderManager().initLoader(DETAIL_LOADER, null, this);
        super.onActivityCreated(savedInstanceState);
    }

    @Override
    public Loader<Cursor> onCreateLoader(int id, Bundle args) {
        Log.v(LOG_TAG, "In onCreateLoader");
        Intent intent = getActivity().getIntent();
        if (intent == null) {
            return null;
        }

        // Now create and return a CursorLoader that will take care of
        // creating a Cursor for the data being displayed.
        return new CursorLoader(getActivity(), intent.getData(),
                FORECAST_COLUMNS, null, null, null);
    }

    @Override
    public void onLoadFinished(Loader<Cursor> loader, Cursor data) {
        Log.v(LOG_TAG, "In onLoadFinished");
        if (!data.moveToFirst()) {
            return;
        }

        String dateString = Utility.formatDate(data
                .getLong(COL_WEATHER_DATE));

        String weatherDescription = data.getString(COL_WEATHER_DESC);

        boolean isMetric = Utility.isMetric(getActivity());

        String high = Utility.formatTemperature(
                data.getDouble(COL_WEATHER_MAX_TEMP), isMetric);

        String low = Utility.formatTemperature(
                data.getDouble(COL_WEATHER_MIN_TEMP), isMetric);

        mForecast = String.format("%s - %s - %s/%s", dateString,
                weatherDescription, high, low);

        TextView detailTextView = (TextView) getView().findViewById(
                R.id.detail_text);
        detailTextView.setText(mForecast);

        // If onCreateOptionsMenu has already happened, we need to update
        // the share intent now.
        if (mShareActionProvider != null) {
            mShareActionProvider
                    .setShareIntent(createShareForecastIntent());
        }
    }

    @Override
    public void onLoaderReset(Loader<Cursor> loader) {
    }
}
}

我试过调试代码，但是

---

-mShareActionProvider给了我null，我不明白这是怎么回事，我想问题是您在XML菜单布局文件中声明了onClick函数，但在代码中没有相应的函数

哪一行有错误？错误在xml文件中。我将android:actionProviderClass更改为app:actionProviderClass

04-13 01:22:51.916: E/AndroidRuntime(20197):    FATAL EXCEPTION: main
04-13 01:22:51.916: E/AndroidRuntime(20197):    Process: com.example.sunshine2,                                        PID: 20197
04-13 01:22:51.916: E/AndroidRuntime(20197):  java.lang.NullPointerException
04-13 01:22:51.916: E/AndroidRuntime(20197):    at    com.example.sunshine2.DetailActivity$DetailFragment.onCreateOptionsMenu(DetailAc    tivity.java:117)
04-13 01:22:51.916: E/AndroidRuntime(20197):    at    android.support.v4.app.Fragment.performCreateOptionsMenu(Fragment.java:1582)
04-13 01:22:51.916: E/AndroidRuntime(20197):    at android.support.v4.app.FragmentManagerImpl.dispatchCreateOptionsMenu(FragmentManager.java:1967)
04-13 01:22:51.916: E/AndroidRuntime(20197):    at android.support.v4.app.FragmentActivity.onCreatePanelMenu(FragmentActivity.java:225)
04-13 01:22:51.916: E/AndroidRuntime(20197):    at android.support.v7.app.ActionBarActivity.superOnCreatePanelMenu(ActionBarActivity.java:232)
04-13 01:22:51.916: E/AndroidRuntime(20197):    at android.support.v7.app.ActionBarActivityDelegateICS.onCreatePanelMenu(ActionBarActivityDelegateICS.java:146)
04-13 01:22:51.916: E/AndroidRuntime(20197):    at android.support.v7.app.ActionBarActivity.onCreatePanelMenu(ActionBarActivity.java:199)
04-13 01:22:51.916: E/AndroidRuntime(20197):    at android.support.v7.app.ActionBarActivityDelegateICS$WindowCallbackWrapper.onCreatePanelMenu(ActionBarActivityDelegateICS.java:293)
04-13 01:22:51.916: E/AndroidRuntime(20197):    at com.android.internal.policy.impl.PhoneWindow.preparePanel(PhoneWindow.java:436)
04-13 01:22:51.916: E/AndroidRuntime(20197):    at com.android.internal.policy.impl.PhoneWindow.doInvalidatePanelMenu(PhoneWindow.java:803)
04-13 01:22:51.916: E/AndroidRuntime(20197):    at com.android.internal.policy.impl.PhoneWindow$1.run(PhoneWindow.java:221)
04-13 01:22:51.916: E/AndroidRuntime(20197):    at android.os.Handler.handleCallback(Handler.java:733)
04-13 01:22:51.916: E/AndroidRuntime(20197):    at android.os.Handler.dispatchMessage(Handler.java:95)
04-13 01:22:51.916: E/AndroidRuntime(20197):    at android.os.Looper.loop(Looper.java:149)
04-13 01:22:51.916: E/AndroidRuntime(20197):    at android.app.ActivityThread.main(ActivityThread.java:5077)
04-13 01:22:51.916: E/AndroidRuntime(20197):    at   java.lang.reflect.Method.invokeNative(Native Method)
04-13 01:22:51.916: E/AndroidRuntime(20197):    at    java.lang.reflect.Method.invoke(Method.java:515)
04-13 01:22:51.916: E/AndroidRuntime(20197):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793)
04-13 01:22:51.916: E/AndroidRuntime(20197):    at     com.android.internal.os.ZygoteInit.main(ZygoteInit.java:609)
04-13 01:22:51.916: E/AndroidRuntime(20197):    at     dalvik.system.NativeStart.main(Native Method)