似乎支持库v4中存在一个错误，我想使用CursorLoader和LoaderManager访问MediaStore音频，我已经遵循协议到T，无论我做什么，都不会调用OnLoaderFinished。
以下是一些代码片段，我创建了一些名为MediaStoreInterface的内容，
MediaStoreInterface的相关部分如下：
public class MediaStoreInterface extends Observable
{
protected Cursor cursor;
protected static final int LOADER_ID1 = 1;
protected static final int LOADER_ID2 = 2;
protected static int lastLoaderId = 0;
protected static String function = "SONGS";
protected static PaudioActivity act;
protected static Sound selectedSound = null;
protected static final String[] projections = {MediaStore.Audio.Media.TITLE, MediaStore.Audio.Media.ARTIST, MediaStore.Audio.Media.DATA};
protected static final String[] projectionsPlaylist = {MediaStore.Audio.Playlists._ID,MediaStore.Audio.Playlists.NAME};
protected static final Uri sourceUri = MediaStore.Audio.Media.EXTERNAL_CONTENT_URI;
protected static final Uri uriPlaylists = MediaStore.Audio.Playlists.EXTERNAL_CONTENT_URI;
protected static ArrayList<String> ret;
protected static boolean done = false;
//Singleton
protected static MediaStoreInterface ref = null;
public static MediaStoreInterface getMusicLibrary(Activity act_)
{
if (ref == null)
ref = new MediaStoreInterface(act_);
return ref;
}
protected MediaStoreInterface(Activity act_)
{
act = (PaudioActivity) act_;
}
public static MediaStoreInterface getMSI()
{
if (android.os.Build.VERSION.SDK_INT < 11)
return MediaStoreInterfaceFrodo.getMusicLibrary(act);
else
return MediaStoreInterfaceHoneyComb.getMusicLibrary(act);
}
protected void loadArray(Cursor data)
{
int num = data.getColumnCount();
if (data == null || !data.moveToFirst())
return;
while(!data.isLast())
{
String s = data.getString(0);
int col = 1;
while(col < num)
s += "|" + data.getString(col++);
ret.add(s);
data.moveToNext();
}
if (function == "SONGS")
numSongs = ret.size();
if (function == "PLAYLISTS")
numPlaylists = ret.size();
cursor = data;
}
public static void setDone()
{
done = true;
}
}
它是一个Singleton，应该为每个API返回正确的MediaStoreInterface， 我将Frodo从这里扩展如下：
import java.util.ArrayList;
import java.util.List;
import android.app.Activity;
import android.database.Cursor;
import android.os.Bundle;
import android.provider.MediaStore;
import android.support.v4.app.LoaderManager;
import android.support.v4.content.CursorLoader;
import android.support.v4.content.Loader;
import android.support.v4.content.Loader.OnLoadCompleteListener;
public class MediaStoreInterfaceFrodo extends MediaStoreInterface implements LoaderManager.LoaderCallbacks<Cursor>, OnLoadCompleteListener<Cursor>
{
public static MediaStoreInterface getMusicLibrary(Activity act_)
{
if (ref == null)
ref = new MediaStoreInterfaceFrodo(act_);
return ref;
}
public void setPaudioActivity(PaudioActivity act_)
{
act = act_;
}
protected MediaStoreInterfaceFrodo(Activity act_)
{
super(act_);
}
public ArrayList<String> getSongList()
{
function = "SONGS";
done = false;
if (ret == null)
ret = new ArrayList<String>();
else
ret.clear();
lastLoaderId = LOADER_ID1;
LoaderManager lm = act.getSupportLoaderManager();
Loader<Cursor> loader1 = lm.getLoader(LOADER_ID1);
if (loader1 != null && loader1.isReset())
loader1 = lm.restartLoader(LOADER_ID1, null, this);
else
{
loader1 = lm.initLoader(LOADER_ID1, null, this);
}
while(!done)
{
waitabit();
}
return ret;
}
public static void editSelectedSongTitle(String newtitle)
{
// TODO Auto-generated method stub
}
public static void setContinuePlayMode(PlayMode pm_)
{
pm = pm_;
}
public List<String> getPlayListNames()
{
function = "PLAYLISTS";
done = false;
if (ret == null)
ret = new ArrayList<String>();
else
ret.clear();
lastLoaderId = LOADER_ID2;
LoaderManager lm = act.getSupportLoaderManager();
lm.initLoader(LOADER_ID2, null, this);
while(!done)
{
waitabit();
}
function = "SONGS";
return ret;
}
@Override
public Loader<Cursor> onCreateLoader(int id, Bundle arg1)
{
CursorLoader cursorLoader = null;
switch (id)
{
case LOADER_ID1:
cursorLoader = new CursorLoader(act, sourceUri, projections, null, null, MediaStore.Audio.Media.TITLE);
break;
case LOADER_ID2:
cursorLoader = new CursorLoader(act, uriPlaylists, projectionsPlaylist, null, null, MediaStore.Audio.Playlists.NAME);
break;
default:
break;
}
cursorLoader.forceLoad();
return cursorLoader;
}
@Override
public void onLoadFinished(Loader<Cursor> cursorLoader, Cursor data)
{
cursor = data;
loadArray(cursor);
done = true;
}
@Override
public void onLoaderReset(Loader<Cursor> arg0)
{
act.getSupportLoaderManager().restartLoader(lastLoaderId, null, ( android.support.v4.app.LoaderManager.LoaderCallbacks<Cursor>) this);
}
@Override
public void onLoadComplete(Loader<Cursor> loader, Cursor data)
{
onLoadFinished( loader, data);
}
}
我试图将数据库查询与我活动中常见的核心和碎片分开，长话短说我有一个按钮，如果单击，则调用getSongList， 我还有setActivity将act成员转换为调用Activity，
我已经阅读了所有相关的StackOverflow文章和Android开发网站上的所有内容。有些人可能会反对我必须在UI线程上调用我的一些函数，我也这样做了，但没有用。我在我的主Activity中实现了相同的代码集，但不管我做什么。永远不会调用OnLoadFinished。
答案 0 :(得分：3)
我不确定导致问题的原因，因为您的代码不完整，但是您的导入意味着您可能不会使用支持包中的活动：
import android.app.Activity;
应该是
import android.support.v4.app.FragmentActivity;
我实际上看不到你的代码如何编译，因为非支持活动没有一个名为getSupportLoaderManager（）的方法
在不知道实际问题是什么的情况下，我将发布我刚刚创建的示例，我将代码归结为实际需要的内容。但请注意，您不必在活动中实现LoaderCallback。正如我测试的那样，这段代码正在运行。
package com.suhw.samples.mediastore;
import android.database.Cursor;
import android.net.Uri;
import android.os.Bundle;
import android.provider.MediaStore;
import android.support.v4.app.FragmentActivity;
import android.support.v4.app.LoaderManager;
import android.support.v4.content.CursorLoader;
import android.support.v4.content.Loader;
import android.util.Log;
public class QueryMediaStoreActivity extends FragmentActivity implements LoaderManager.LoaderCallbacks<Cursor> {
private final static String TAG = "QueryMediaStoreActivity";
private static final int LOADER_ID1 = 1;
private static final String[] audioMediaProjection = {MediaStore.Audio.Media.TITLE, MediaStore.Audio.Media.ARTIST, MediaStore.Audio.Media.DATA};
private static final Uri audioMediaUri = MediaStore.Audio.Media.EXTERNAL_CONTENT_URI;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
LoaderManager loaderManager = getSupportLoaderManager();
loaderManager.initLoader(LOADER_ID1, null, this);
}
@Override
public Loader<Cursor> onCreateLoader(int id, Bundle bundle) {
switch (id) {
case LOADER_ID1:
return new CursorLoader(this, audioMediaUri, audioMediaProjection, null, null, MediaStore.Audio.Media.TITLE);
default:
return null;
}
}
@Override
public void onLoadFinished(Loader<Cursor> cursorLoader, Cursor cursor) {
switch (cursorLoader.getId()) {
case LOADER_ID1:
Log.d(TAG, "onLoadFinished called:\n\tcursorCount:" + cursor.getCount());
break;
}
}
@Override
public void onLoaderReset(Loader<Cursor> cursorLoader) {
}
}
答案 1 :(得分：1)
更改 OncreateLoader （），如果处理多个Loader，请更好地使用switch()语句。
@Override
public Loader<Cursor> onCreateLoader(int id, Bundle arg1)
{
CursorLoader cursorLoader = null;
switch (id) {
case LOADER_ID1:
cursorLoader = new CursorLoader(getActivity(), sourceUri, projections, null, null, MediaStore.Audio.Media.TITLE);
break;
case LOADER_ID2:
cursorLoader = new CursorLoader(getActivity(), uriPlaylists, projectionsPlaylist, null, null, MediaStore.Audio.Playlists.NAME);
break;
default:
break;
}
cursorLoader.forceLoad();
return cursorLoader;
}
编辑： -
使用getActivity()代替act了解详情CursorLoader
注意： - 方法getLoaderManager（）仅在Fragment类中可用。要在FragmentActivity中获取LoaderManager，请调用getSupportLoaderManager（）。
试试这样。