Question

这是我的Manifest.xml：

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.example.testcode"
    android:versionCode="1"
    android:versionName="1.0" >


    <uses-permission android:name="android.permission.READ_CONTACTS"/>
    <uses-sdk android:minSdkVersion="15" />

    <application

        android:icon="@drawable/ic_launcher"
        android:label="@string/app_name" >

            <activity android:label="@string/app_name" android:name=".TestAndActivity">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
        </application>

</manifest>

这是我的班级：

package com.example.testcode;

import android.app.ListFragment;
import android.app.LoaderManager;
import android.content.CursorLoader;
import android.content.Loader;
import android.database.Cursor;
import android.net.Uri;
import android.os.Bundle;
import android.provider.ContactsContract;
import android.support.v4.widget.SimpleCursorAdapter;
import android.text.TextUtils;
import android.util.Log;
import android.view.Menu;
import android.view.MenuInflater;
import android.view.MenuItem;
import android.view.View;
import android.widget.ListView;
import android.widget.SearchView;
import android.widget.SearchView.OnQueryTextListener;

public class TestAndActivity extends ListFragment
        implements OnQueryTextListener, LoaderManager.LoaderCallbacks<Cursor> {

    // This is the Adapter being used to display the list's data.
    SimpleCursorAdapter mAdapter;

    // If non-null, this is the current filter the user has provided.
    String mCurFilter;

    @Override 
    public void onActivityCreated(Bundle savedInstanceState) {
        super.onActivityCreated(savedInstanceState);

        // Give some text to display if there is no data.  In a real
        // application this would come from a resource.
        setEmptyText("No phone numbers");

        // We have a menu item to show in action bar.
        setHasOptionsMenu(true);

        // Create an empty adapter we will use to display the loaded data.
        mAdapter = new SimpleCursorAdapter(getActivity(),
                android.R.layout.simple_list_item_2, null,
                new String[] { ContactsContract.Contacts.DISPLAY_NAME, ContactsContract.Contacts.CONTACT_STATUS },
                new int[] { android.R.id.text1, android.R.id.text2 }, 0);
        setListAdapter(mAdapter);

        // Start out with a progress indicator.
        setListShown(false);

        // Prepare the loader.  Either re-connect with an existing one,
        // or start a new one.
        getLoaderManager().initLoader(0, null, this);
    }

    @Override public void onCreateOptionsMenu(Menu menu, MenuInflater inflater) {
        // Place an action bar item for searching.
        MenuItem item = menu.add("Search");
        item.setIcon(android.R.drawable.ic_menu_search);
        item.setShowAsAction(MenuItem.SHOW_AS_ACTION_IF_ROOM);
        SearchView sv = new SearchView(getActivity());
        sv.setOnQueryTextListener(this);
        item.setActionView(sv);
    }

    public boolean onQueryTextChange(String newText) {
        // Called when the action bar search text has changed.  Update
        // the search filter, and restart the loader to do a new query
        // with this filter.
        mCurFilter = !TextUtils.isEmpty(newText) ? newText : null;
        getLoaderManager().restartLoader(0, null, this);
        return true;
    }

    @Override public boolean onQueryTextSubmit(String query) {
        // Don't care about this.
        return true;
    }

    @Override public void onListItemClick(ListView l, View v, int position, long id) {
        // Insert desired behavior here.

        Log.i("FragmentComplexList", "Item clicked: " + id);
    }

    // These are the Contacts rows that we will retrieve.
    static final String[] CONTACTS_SUMMARY_PROJECTION = new String[] {
        ContactsContract.Contacts._ID,
        ContactsContract.Contacts.DISPLAY_NAME,
        ContactsContract.Contacts.CONTACT_STATUS,
        ContactsContract.Contacts.CONTACT_PRESENCE,
        ContactsContract.Contacts.PHOTO_ID,
        ContactsContract.Contacts.LOOKUP_KEY,
    };

    public Loader<Cursor> onCreateLoader(int id, Bundle args) {
        // This is called when a new Loader needs to be created.  This
        // sample only has one Loader, so we don't care about the ID.
        // First, pick the base URI to use depending on whether we are
        // currently filtering.
        Uri baseUri;
        if (mCurFilter != null) {
            baseUri = Uri.withAppendedPath(ContactsContract.Contacts.CONTENT_FILTER_URI,
                    Uri.encode(mCurFilter));
        } else {
            baseUri = ContactsContract.Contacts.CONTENT_URI;
        }

        // Now create and return a CursorLoader that will take care of
        // creating a Cursor for the data being displayed.
        String select = "((" + ContactsContract.Contacts.DISPLAY_NAME + " NOTNULL) AND ("
                + ContactsContract.Contacts.HAS_PHONE_NUMBER + "=1) AND ("
                + ContactsContract.Contacts.DISPLAY_NAME + " != '' ))";
        return new CursorLoader(getActivity(), baseUri,
                CONTACTS_SUMMARY_PROJECTION, select, null,
                ContactsContract.Contacts.DISPLAY_NAME + " COLLATE LOCALIZED ASC");
    }

    public void onLoadFinished(Loader<Cursor> loader, Cursor data) {
        // Swap the new cursor in.  (The framework will take care of closing the
        // old cursor once we return.)
        mAdapter.swapCursor(data);

        // The list should now be shown.
        if (isResumed()) {
            setListShown(true);
        } else {
            setListShownNoAnimation(true);
        }
    }

    public void onLoaderReset(Loader<Cursor> loader) {
        // This is called when the last Cursor provided to onLoadFinished()
        // above is about to be closed.  We need to make sure we are no
        // longer using it.
        mAdapter.swapCursor(null);
    }
}

这是Android中Loaders的基本实现，它从手机获取联系人并显示它们。错误：

Caused by: java.lang.ClassCastException: com.example.testcode.TestAndActivity cannot be cast to android.app.Activity

Answer 1

Hiccup，你得到了异常，因为你试图将应用程序启动Activity设置为Fragment（即，TestAndActivity不是一个Activity，因为它扩展了ListFragmant）：

<activity android:label="@string/app_name" android:name=".TestAndActivity">

使用fragmanents时，它们必须存在于Activity中。阅读the Android Development page here with regard to Fragments。基本上，要解决这个问题，您需要创建一个正常的活动来启动，然后将Fragment放入活动中。

您需要阅读的开发人员中的特定部分是Adding a fragment to an activity

Android应用程序中的java.lang.ClassNotFoundException。

1 个答案: