我有一个带有AutoCompleteTextView的Activity。在您键入时，AutoCompleteTextView会从您的联系人中查找匹配的名称，并将其显示在列表中。如果在显示此列表时更改了设备方向，则活动崩溃（源代码后提供错误消息）。
我正在为ICS 4.0.3开发并在Nexus S设备上进行测试。我试图遵循使用LoaderManager生成和管理游标的最佳实践。我的理解是LoaderManager应该在方向更改（http://developer.android.com/guide/topics/fundamentals/loaders.html#callback）之间保留游标数据，但似乎并非如此。
因为当过滤约束太小而无法使用时，CursorAdapter要我返回原始未过滤的游标，我是：
问题似乎是在方向更改后调用了onLoadFinished LoaderManager回调，但是在重新定向期间它正在传递的光标（原始光标？）被关闭。
如果我通过在清单中的activity声明中添加以下内容来配置我的活动以管理方向更改：
机器人：configChanges = “取向|屏幕尺寸”
保存的原始光标应该在方向更改中保留（对吗？）。虽然应用程序没有崩溃，但还会出现另一个相关问题：
在这种情况下，我的原始光标似乎也消失了。我猜测应用程序没有崩溃，因为当我的活动配置为自行管理方向更改时，不会调用onLoadFinished回调
查看 - home.xml
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical" >
<AutoCompleteTextView
android:id="@+id/newPlayer_edit"
android:inputType="text"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_gravity="center_horizontal"
android:hint="Contact"
android:singleLine="true" >
<requestFocus />
</AutoCompleteTextView>
</LinearLayout>
活动 - Home.java
public class Home extends Activity implements LoaderManager.LoaderCallbacks<Cursor> {
// Constants
private static final String TAG = "HOME";
private static final boolean DEBUG = true;
public static final int LOADER_CONTACTS_CURSOR = 1;
// Variables
private AdapterContacts adapter;
public static Cursor originalCursor = null;
/**
* Overrides
*/
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
// Set the view
setContentView(R.layout.home);
// Initialize CursorAdapter
adapter = new AdapterContacts(this, null, 0);
// Attach CursorAdapter to AutoCompleteTextView field
AutoCompleteTextView field = (AutoCompleteTextView) findViewById(R.id.newPlayer_edit);
field.setAdapter(adapter);
// Initialize Cursor using LoaderManager
LoaderManager.enableDebugLogging(true);
getLoaderManager().initLoader(LOADER_CONTACTS_CURSOR, null, this);
}
@Override
public void onDestroy() {
if (DEBUG) Log.i(TAG, "Destroying activity");
super.onDestroy();
}
@Override
public Loader<Cursor> onCreateLoader(int id, Bundle args) {
if (DEBUG) Log.i(TAG, "Loader Callback: creating loader");
return new CursorLoader(this, ContactsContract.Contacts.CONTENT_URI, null, null, null, null);
}
@Override
public void onLoadFinished(Loader<Cursor> loader, Cursor cursor) {
if (DEBUG) Log.i(TAG, "Loader Callback: load finished");
// If no cursor has been loaded before, reserve this cursor as the original
// It will be returned by the CursorAdapter when the filter constraint is null
if (originalCursor == null) {
originalCursor = cursor;
}
// add the cursor to the adapter
adapter.swapCursor(cursor);
}
@Override
public void onLoaderReset(Loader<Cursor> loader) {
if (DEBUG) Log.i(TAG, "Loader Callback: resetting");
adapter.swapCursor(null);
}
}
CursorAdapter - AdapterContacts.java
public class AdapterContacts extends CursorAdapter {
// Constants
private static final String TAG = "AdapterContacts";
private static final boolean DEBUG = true;
// Variables
private TextView mName;
private ContentResolver mContent;
/**
* Constructor
*/
public AdapterContacts(Context context, Cursor c, int flags) {
super(context, c, flags);
mContent = context.getContentResolver();
}
/**
* Overrides
*/
@Override
public View newView(Context context, Cursor cursor, ViewGroup parent) {
// Inflate the views that create each row of the dropdown list
final LayoutInflater inflater = LayoutInflater.from(context);
final LinearLayout ret = new LinearLayout(context);
ret.setOrientation(LinearLayout.VERTICAL);
mName = (TextView) inflater.inflate(android.R.layout.simple_dropdown_item_1line, parent, false);
ret.addView(mName, new LinearLayout.LayoutParams(LayoutParams.WRAP_CONTENT, LayoutParams.WRAP_CONTENT));
/*
int nameIdx = cursor.getColumnIndexOrThrow(ContactsContract.Contacts.DISPLAY_NAME_PRIMARY);
mName.setText(cursor.getString(nameIdx));
*/
return ret;
}
@Override
public void bindView(View view, Context context, Cursor cursor) {
// Fill the dropdown row with data from the cursor
int nameIdx = cursor.getColumnIndexOrThrow(ContactsContract.Contacts.DISPLAY_NAME_PRIMARY);
String name = cursor.getString(nameIdx);
((TextView) ((LinearLayout) view).getChildAt(0)).setText(name);
}
@Override
public String convertToString(Cursor cursor) {
// Convert the dropdown list entry that the user clicked on
// into a string that will fill the AutoCompleteTextView
int nameCol = cursor.getColumnIndexOrThrow(ContactsContract.Contacts.DISPLAY_NAME_PRIMARY);
return cursor.getString(nameCol);
}
@Override
public void changeCursor(Cursor newCursor) {
// Because a LoaderManager is used to initialize the originalCursor
// changeCursor (which closes cursors be default when they're released)
// is overridden to use swapCursor (which doesn't close cursors).
Cursor oldCursor = swapCursor(newCursor);
// Any swapped out cursors that are not the original cursor must
// then be closed manually.
if (oldCursor != Home.originalCursor) {
oldCursor.close();
}
}
@Override
public Cursor runQueryOnBackgroundThread(CharSequence constraint) {
// If their is a constraint, generate and return a new cursor
if (constraint != null) {
// I'd love to use a LoaderManager here too,
// but haven't quite figured out the best way.
if (DEBUG) Log.i(TAG, "Constraint is not null: " + constraint.toString());
Uri uri = Uri.withAppendedPath(ContactsContract.Contacts.CONTENT_FILTER_URI, constraint.toString());
return mContent.query(uri, null, null, null, null);
}
// If no constraint, return the originalCursor
if (DEBUG) Log.i(TAG, "Constraint is null");
return Home.originalCursor;
}
}
错误消息
03-16 10:39:34.839: E/AndroidRuntime(22097): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.myapp.basic/com.myapp.basic.Home}: android.database.StaleDataException: Attempted to access a cursor after it has been closed.
03-16 10:39:34.839: E/AndroidRuntime(22097): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1956)
03-16 10:39:34.839: E/AndroidRuntime(22097): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1981)
03-16 10:39:34.839: E/AndroidRuntime(22097): at android.app.ActivityThread.handleRelaunchActivity(ActivityThread.java:3351)
03-16 10:39:34.839: E/AndroidRuntime(22097): at android.app.ActivityThread.access$700(ActivityThread.java:123)
03-16 10:39:34.839: E/AndroidRuntime(22097): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1151)
03-16 10:39:34.839: E/AndroidRuntime(22097): at android.os.Handler.dispatchMessage(Handler.java:99)
03-16 10:39:34.839: E/AndroidRuntime(22097): at android.os.Looper.loop(Looper.java:137)
03-16 10:39:34.839: E/AndroidRuntime(22097): at android.app.ActivityThread.main(ActivityThread.java:4424)
03-16 10:39:34.839: E/AndroidRuntime(22097): at java.lang.reflect.Method.invokeNative(Native Method)
03-16 10:39:34.839: E/AndroidRuntime(22097): at java.lang.reflect.Method.invoke(Method.java:511)
03-16 10:39:34.839: E/AndroidRuntime(22097): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:784)
03-16 10:39:34.839: E/AndroidRuntime(22097): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:551)
03-16 10:39:34.839: E/AndroidRuntime(22097): at dalvik.system.NativeStart.main(Native Method)
03-16 10:39:34.839: E/AndroidRuntime(22097): Caused by: android.database.StaleDataException: Attempted to access a cursor after it has been closed.
03-16 10:39:34.839: E/AndroidRuntime(22097): at android.database.BulkCursorToCursorAdaptor.throwIfCursorIsClosed(BulkCursorToCursorAdaptor.java:75)
03-16 10:39:34.839: E/AndroidRuntime(22097): at android.database.BulkCursorToCursorAdaptor.getColumnNames(BulkCursorToCursorAdaptor.java:170)
03-16 10:39:34.839: E/AndroidRuntime(22097): at android.database.AbstractCursor.getColumnIndex(AbstractCursor.java:248)
03-16 10:39:34.839: E/AndroidRuntime(22097): at android.database.AbstractCursor.getColumnIndexOrThrow(AbstractCursor.java:265)
03-16 10:39:34.839: E/AndroidRuntime(22097): at android.database.CursorWrapper.getColumnIndexOrThrow(CursorWrapper.java:78)
03-16 10:39:34.839: E/AndroidRuntime(22097): at android.widget.CursorAdapter.swapCursor(CursorAdapter.java:338)
03-16 10:39:34.839: E/AndroidRuntime(22097): at com.myapp.basic.Home.onLoadFinished(Home.java:70)
03-16 10:39:34.839: E/AndroidRuntime(22097): at com.myapp.basic.Home.onLoadFinished(Home.java:1)
03-16 10:39:34.839: E/AndroidRuntime(22097): at android.app.LoaderManagerImpl$LoaderInfo.callOnLoadFinished(LoaderManager.java:438)
03-16 10:39:34.839: E/AndroidRuntime(22097): at android.app.LoaderManagerImpl$LoaderInfo.finishRetain(LoaderManager.java:309)
03-16 10:39:34.839: E/AndroidRuntime(22097): at android.app.LoaderManagerImpl.finishRetain(LoaderManager.java:765)
03-16 10:39:34.839: E/AndroidRuntime(22097): at android.app.Activity.performStart(Activity.java:4485)
03-16 10:39:34.839: E/AndroidRuntime(22097): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1929)
03-16 10:39:34.839: E/AndroidRuntime(22097): ... 12 more
警告消息 - 将活动配置为自行管理方向更改时
03-16 10:47:50.804: W/Filter(22739): An exception occured during performFiltering()!
03-16 10:47:50.804: W/Filter(22739): android.database.StaleDataException: Attempted to access a cursor after it has been closed.
03-16 10:47:50.804: W/Filter(22739): at android.database.BulkCursorToCursorAdaptor.throwIfCursorIsClosed(BulkCursorToCursorAdaptor.java:75)
03-16 10:47:50.804: W/Filter(22739): at android.database.BulkCursorToCursorAdaptor.getCount(BulkCursorToCursorAdaptor.java:81)
03-16 10:47:50.804: W/Filter(22739): at android.database.CursorWrapper.getCount(CursorWrapper.java:57)
03-16 10:47:50.804: W/Filter(22739): at android.widget.CursorFilter.performFiltering(CursorFilter.java:53)
03-16 10:47:50.804: W/Filter(22739): at android.widget.Filter$RequestHandler.handleMessage(Filter.java:234)
03-16 10:47:50.804: W/Filter(22739): at android.os.Handler.dispatchMessage(Handler.java:99)
03-16 10:47:50.804: W/Filter(22739): at android.os.Looper.loop(Looper.java:137)
03-16 10:47:50.804: W/Filter(22739): at android.os.HandlerThread.run(HandlerThread.java:60)
答案 0 :(得分：6)
我发现问题的解决方案（解决方案）分为两部分：
注意：对于任何关注的人，我在运行此代码时仍然会遇到一些错误，但这并不是致命的，它似乎与游标无关，所以我没有解决它这里。的
最大的复杂因素是CursorAdapter中的runQueryOnBackgroundThread方法要求返回游标。当使用LoaderManager时，在异步回调之前你不会触及游标，这有缺点：
runQueryOnBackgroundThread方法中生成和检索光标。runQueryOnBackgroundThread是使用新过滤约束调用的第一个方法。runQueryOnBackgroundThread方法将光标移到changeCursor方法，该方法关闭更改的游标（使用LoaderManager / CursorLoader时我们不做的事情），所以我们不要无论如何都不想遵循这个工作流程。默认情况下，CursorAdapter的runQueryOnBackgroundThread方法只调用CursorAdapter的FilterQueryProvider的runQuery方法（如果已定义）。我选择定义FilterQueryProvider而不是覆盖runQueryOnBackgroundThread方法，原因如下：
注意：runQuery方法仍然需要返回游标，因此我们不能解决这个问题。
我决定在我的FilterQueryProvider的runQuery方法中生成一个虚拟光标。然后，由于该虚拟光标将被移交给CursorAdapter的changeCursor方法，我会覆盖changeCursor以简单地关闭它传递的每个光标。
runQuery方法还会启动包含过滤约束的异步LoaderManager调用。然后，LoaderManager回调负责交换生成的新游标。
注意：理想情况下，我认为您可以覆盖调用runQueryOnBackgroundThread的函数，并让它调用异步LoaderManager，但我无法弄清楚它是什么。 < / p>
我试图区分未过滤和过滤的游标，当过滤约束为空时，可以使用未过滤的游标。在无条件阅读Android 3.0 - what are the advantages of using LoaderManager instances exactly?之后，我意识到接受的答案是使用相同的CursorLoader来生成所有游标。
我没有试图挂在原始的未过滤光标上，而是决定在需要时我只生成一个新的未过滤光标。 onCreateLoader LoaderManager回调变得有点复杂（但更像我见过的例子），onLoadFinished回调变得更加简单（就像我见过的例子）。
活动 - home.java
public class Home extends Activity implements LoaderManager.LoaderCallbacks<Cursor> {
// Constants
private static final String TAG = "Home";
private static final boolean DEBUG = true;
public static final int LOADER_CONTACTS_CURSOR = 1;
// Variables
private AdapterContacts adapter;
/**
* Overrides
*/
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
// Set the view
setContentView(R.layout.home);
// Initialize CursorAdapter
adapter = new AdapterContacts(this, null, 0);
final LoaderManager.LoaderCallbacks<Cursor> iFace = this;
adapter.setFilterQueryProvider(new FilterQueryProvider() {
public Cursor runQuery(CharSequence constraint) {
if (constraint != null) {
Bundle bundle = new Bundle();
bundle.putCharSequence("constraint", constraint);
getLoaderManager().restartLoader(Home.LOADER_CONTACTS_CURSOR, bundle, iFace);
} else {
getLoaderManager().restartLoader(Home.LOADER_CONTACTS_CURSOR, null, iFace);
}
return getContentResolver().query(ContactsContract.Contacts.CONTENT_URI, null, null, null, null);
}
});
// Attach CursorAdapter to AutoCompleteTextView field
AutoCompleteTextView field = (AutoCompleteTextView) findViewById(R.id.newPlayer_edit);
field.setAdapter(adapter);
// Initialize Cursor using LoaderManagers
LoaderManager.enableDebugLogging(true);
getLoaderManager().initLoader(LOADER_CONTACTS_CURSOR, null, this);
}
@Override
public void onDestroy() {
if (DEBUG) Log.i(TAG, "Destroying activity");
super.onDestroy();
}
@Override
public Loader<Cursor> onCreateLoader(int id, Bundle args) {
if (DEBUG) Log.i(TAG, "Loader Callback: creating loader");
Uri baseUri;
if (args != null) {
CharSequence constraint = args.getCharSequence("constraint");
if (DEBUG) Log.i(TAG, "Constraint: " + constraint.toString());
baseUri = Uri.withAppendedPath(ContactsContract.Contacts.CONTENT_FILTER_URI, Uri.encode(constraint.toString()));
} else {
if (DEBUG) Log.i(TAG, "No Constraint");
baseUri = ContactsContract.Contacts.CONTENT_URI;
}
return new CursorLoader(this, baseUri, null, null, null, null);
}
@Override
public void onLoadFinished(Loader<Cursor> loader, Cursor cursor) {
if (DEBUG) Log.i(TAG, "Loader Callback: load finished");
adapter.swapCursor(cursor);
}
@Override
public void onLoaderReset(Loader<Cursor> loader) {
if (DEBUG) Log.i(TAG, "Loader Callback: resetting");
adapter.swapCursor(null);
}
}
CursorAdapter - AdapterContacts.java
public class AdapterContacts extends CursorAdapter {
// Constants
private static final String TAG = "AdapterContacts";
private static final boolean DEBUG = true;
// Variables
private TextView mName;
/**
* Constructor
*/
public AdapterContacts(Context context, Cursor c, int flags) {
super(context, c, flags);
}
/**
* Overrides
*/
@Override
public View newView(Context context, Cursor cursor, ViewGroup parent) {
// Inflate the views that create each row of the dropdown list
final LayoutInflater inflater = LayoutInflater.from(context);
final LinearLayout ret = new LinearLayout(context);
ret.setOrientation(LinearLayout.VERTICAL);
mName = (TextView) inflater.inflate(android.R.layout.simple_dropdown_item_1line, parent, false);
ret.addView(mName, new LinearLayout.LayoutParams(LayoutParams.WRAP_CONTENT, LayoutParams.WRAP_CONTENT));
/*
int nameIdx = cursor.getColumnIndexOrThrow(ContactsContract.Contacts.DISPLAY_NAME_PRIMARY);
mName.setText(cursor.getString(nameIdx));
*/
return ret;
}
@Override
public void bindView(View view, Context context, Cursor cursor) {
// Fill the dropdown row with data from the cursor
int nameIdx = cursor.getColumnIndexOrThrow(ContactsContract.Contacts.DISPLAY_NAME_PRIMARY);
String name = cursor.getString(nameIdx);
((TextView) ((LinearLayout) view).getChildAt(0)).setText(name);
}
@Override
public String convertToString(Cursor cursor) {
// Convert the dropdown list entry that the user clicked on
// into a string that will fill the AutoCompleteTextView
int nameCol = cursor.getColumnIndexOrThrow(ContactsContract.Contacts.DISPLAY_NAME_PRIMARY);
return cursor.getString(nameCol);
}
@Override
public void changeCursor(Cursor newCursor) {
newCursor.close();
}
}
答案 1 :(得分：0)
如果您使用Loader来管理Adapter的{{1}}，那么您需要不惜一切代价避免使用Cursor。由于适配器中的adapter.filter()需要返回filter()这是不可能的，因为加载器是异步的并且在后台线程中运行。
如何用加载器替换Cursor：
在onSelect / Item / TextInput侦听器中，将选定/输入值存储在类变量中。
将所有对adapter.filter()的来电替换为myAdapter.filter()。
在myLoadManager.restartLoader(...)方法中，使用您现在拥有的存储的选定/输入值，因为步骤1，动态生成您的sql / cursor查询并运行它。
这就是事件顺序的演绎方式：
用户选择一个微调器下拉列表并选择“USA”。
您将“USA”存储在类变量中，然后调用onCreateLoader()。
加载管理器会销毁之前的加载管理器，并创建一个名为myLoadManager.restartLoader(...)的新加载管理器，其中包含您自动生成的查询代码。
新加载程序运行更新的查询并通知您的适配器刷新＆amp;重绘它的数据。
为什么要使用onCreateLoader()？
基于慢速数据的非阻塞UI更新的免费/更轻松的异步管理。比Loaders容易得多。
游标的可用内存管理。在重新查询或活动结束时自动清除/关闭AsyncTasks。