那些遇到过的问题

使用AutoCompleteTextView和CursorAdapter时,更改设备方向会导致活动崩溃

los*_*ime 3 java android

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(源代码后提供的错误消息).

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应该在方向更改中保留游标数据(http://developer.android.com/guide/topics/fundamentals/loaders.html#callback),但似乎并非如此.

因为当过滤约束太小而无法使用时,CursorAdapter要我返回原始的未过滤游标,我是:

  1. 将光标保存为活动的静态变量,以便在不符合过滤条件时使用(对不当的术语表示抱歉.我是Java新手).
  2. 防止CursorAdapter在替换游标后关闭游标,除非通过将游标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onLoadFinished LoaderManager回调,但是在重新定向期间,它传递的光标(原始光标？)被关闭.

如果我通过将以下内容添加到activity清单中的声明来配置我的Activity以管理方向更改:

机器人:configChanges = "方向|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:

  • 如果我键入几个字母,更改设备方向,然后开始删除字母,一旦我得到1或0个字母,LogCat会给我一个警告,我正在尝试访问光标关闭后.

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,因为我的活动配置为管理方向更改本身时未调用onLoadFinished回调

我的问题

  1. 我正确地假设我的光标在设备方向改变时被破坏了吗？
  2. 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>
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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);
}
}
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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;
}
}
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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
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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)
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los*_*ime 6

我发现我的问题的解决方案(解决方案)分为两部分:

  1. 我无法在CursorAdapter中手动继续生成游标.我不得不开始使用Loader Manager
  2. 我不需要坚持使用任何游标.

注意:对于任何关注者,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,所以我不在这里解决它.

在CursorAdapter中生成游标

最大的复杂因素是runQueryOnBackgroundThreadCursorAdapter 中的方法需要返回游标.当使用LoaderManager时,在异步回调之前你不会触及游标,并且有缺点:

  1. 您无法从runQueryOnBackgroundThread方法中生成和检索游标.
  2. 您无法提前生成游标,因为这runQueryOnBackgroundThread是使用新过滤约束调用的第一个方法.
  3. 该runQueryOnBackgroundThread方法的手光标从该changeCursor方法,这将关闭该改变了(什么用LoaderManager/CursorLoader工作时,我们不这样做)的游标,所以我们不想遵循这一流程反正.

默认情况下,runQueryOnBackgroundThreadCursorAdapter的runQuery方法只调用CursorAdapter的FilterQueryProvider方法(如果已定义).我选择定义FilterQueryProvider而不是覆盖该runQueryOnBackgroundThread方法有以下几个原因:

  • FilterQueryProvider可以从实例化CursorAdapter的Activity中定义,并且使用Activity中的LoaderManager更容易从CursorAdapter中使用它.
  • 如果可能的话,我更愿意让代码按照它的意图去做.

注意:该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 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,因此我会覆盖它changeCursor以简单地关闭它传递的每个光标.

该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,我认为您可以覆盖调用的函数runQueryOnBackgroundThread,并让它调用异步LoaderManager,但我无法弄清楚它是什么.

挂在游标上

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.阅读Android 3.0后 - 使用LoaderManager实例的优势是什么？无数次,我意识到接受的答案是使用相同的CursorLoader来生成所有游标.

我没有尝试继续使用原始的未过滤光标,而是决定在需要时生成一个新的未过滤光标.该onCreateLoaderLoaderManager回调变得有点更复杂(但更像我已经看到了例子),以及onLoadFinished回调变得更加简单(如例子我已经看到).

源代码

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);
}
}
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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();
}
}
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