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java - 使用 AutoCompleteTextView 和 CursorAdapter 时，更改设备方向会导致 Activity 崩溃

情况

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姓名并将其显示在列表中。如果在显示此列表时更改设备方向，则 Activity 将崩溃(源代码后提供错误消息)。

笔记

我正在为 ICS 4.0.3 开发并在 Nexus S 设备上进行测试。我正在尝试遵循使用 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 ) 中保留光标数据，但情况似乎并非如此。

因为 CursorAdapter 要我在过滤约束太小而无法使用时返回原始的、未过滤的游标，所以我是:

  • 将光标保存为 Activity 的静态变量，以在不满足过滤条件时使用(抱歉，术语不当。我是 Java 新手)。
  • 防止 CursorAdapter 在替换游标后关闭游标，除非它通过与保存的游标进行比较来确认它不是原始游标。

    • 问题似乎是在方向更改后调用了 onLoadFinished LoaderManager 回调，但它传递的游标(原始游标？)在重新定位期间已关闭。

    如果我将 Activity 配置为通过将以下内容添加到 list 中的 activity 声明来管理方向更改本身:



    保存的原始光标应在方向更改时保留(对吗？)。虽然应用程序没有崩溃，但会出现另一个相关问题:
  • 如果我输入几个字母，更改设备方向，然后开始删除字母，一旦我减少到 1 或 0 个字母，LogCat 就会警告我我正在尝试访问关闭的光标。

    • 在这种情况下，我的原始光标似乎也消失了。我猜应用程序没有崩溃，因为当我的 Activity 配置为自行管理方向更改时，没有调用 onLoadFinished 回调

    我的问题
  • 我是否正确地假设我的光标在设备方向改变时被破坏？
  • 如何在设备方向改变时保留光标和/或其数据？

    • 源代码

    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>

    Activity - 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;
}
}

    错误信息
    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 - 当 Activity 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)

    最佳答案

    我发现我的问题的解决方案(解决方案)分为两部分:

  • 我无法继续在 CursorAdapter 中手动生成游标。我不得不开始使用 Loader Manager
  • 我不需要卡在任何游标上。

    • 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，但这不是致命的，而且它似乎与游标无关，所以我不在这里解决它。

    在 CursorAdapter 中生成游标

    最大的复杂之处在于 CursorAdapter 中的 runQueryOnBackgroundThread 方法要求返回一个游标。使用 LoaderManager 时，在异步回调之前您不会接触游标，这有缺点:
  • 您不能从 runQueryOnBackgroundThread 方法中生成和检索游标。
  • 您不能提前生成游标，因为 runQueryOnBackgroundThread 是第一个使用新过滤约束调用的方法。
  • runQueryOnBackgroundThread 方法将其光标交给 changeCursor 方法，该方法关闭已更改的光标(在使用 LoaderManager/CursorLoader 时我们不会这样做)，因此无论如何我们都不想遵循该工作流程。

    • 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)。出于以下几个原因，我选择定义 FilterQueryProvider 而不是覆盖 runQueryOnBackgroundThread 方法:
  • FilterQueryProvider 可以从实例化 CursorAdapter 的 Activity 定义，并且从 Activity 使用 LoaderManager 比在 CursorAdapter 内使用它更容易。
  • 如果可能的话，我更愿意让代码做它应该做的事情。

    • 注意: runQuery 方法仍然需要返回一个游标，所以我们不能回避这个问题。

    我决定在我的 FilterQueryProvider 的 runQuery 方法中生成一个虚拟游标。然后，由于该虚拟游标将移交给 CursorAdapter 的 changeCursor 方法，因此我覆盖了 changeCursor 以简单地关闭它传递的每个游标。
    runQuery 方法还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，我想您可以覆盖调用 runQueryOnBackgroundThread 的函数，并让它进行异步 LoaderManager 调用，但我不知道那是什么。

    卡在光标上

    我试图区分未过滤的游标和过滤的游标，以便在过滤约束为空时可以使用未过滤的游标。在无数次阅读 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。

    我没有尝试保留原始的未过滤游标，而是决定在需要时生成一个新的未过滤游标。 onCreateLoader LoaderManager 回调变得有点复杂(但更像我看到的示例)，而 onLoadFinished 回调变得更加简单(就像我看到的示例)。

    源代码

    Activity - 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();
}
}

    关于java - 使用 AutoCompleteTextView 和 CursorAdapter 时，更改设备方向会导致 Activity 崩溃，我们在Stack Overflow上找到一个类似的问题：https://stackoverflow.com/questions/9742017/

    10-12 03:11
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