源数据更改时加载程序不加载数据

Question

Android 文档指出 LOADERS - 它们监控数据源并在内容更改时提供新结果。我已将 CursorAdapter 更改为适用于 SQLite 数据库。

import android.content.ContentResolver;
import android.content.Context;
import android.database.ContentObserver;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.support.v4.content.AsyncTaskLoader;
import android.support.v4.content.Loader.ForceLoadContentObserver;
import android.util.Log;


public class SimpleCursorLoader extends AsyncTaskLoader<Cursor> {

final ForceLoadContentObserver mObserver;

String mTable;
String[] mColumns;
String mSelection;
String[] mSelectionArgs;
String mGroupBy;
String mHaving;
String mOrderBy;
String mLimit;

Cursor mCursor;
SQLiteDatabase mDb;
 /**
 * Creates an empty unspecified CursorLoader.  You must follow this with
 * calls to {@link #setUri(Uri)}, {@link #setSelection(String)}, etc
 * to specify the query to perform.
 */
public SimpleCursorLoader(Context context) {
    super(context);
    mObserver = new ForceLoadContentObserver();
}

/**
 * Creates a fully-specified SimpleCursorLoader.  See
 * {@link ContentResolver#query(Uri, String[], String, String[], String)
 * ContentResolver.query()} for documentation on the meaning of the
 * parameters.  These will be passed as-is to that call.
 */
public SimpleCursorLoader(Context context,String table, String[] columns, String      selection, 
        String[] selectionArgs, String groupBy, String having, String orderBy, String limit, SQLiteDatabase db) {

    super(context);
    mObserver = new ForceLoadContentObserver();
    mTable = table;
    mColumns = columns; //copying array
    mSelection = selection;
    mSelectionArgs = selectionArgs;
    mGroupBy = groupBy;
    mHaving = having;
    mOrderBy =  orderBy;
    mLimit = limit;
    mDb = db;
}       

    /* Runs on a worker thread */
@Override
public Cursor loadInBackground() {
    Cursor cursor = mDb.query(mTable, mColumns, mSelection, mSelectionArgs, mGroupBy, mHaving, mOrderBy, mLimit);
    if (cursor != null) {
        // Ensure the cursor window is filled
        cursor.getCount();
        Log.d("SimpleCursorLoader","Cursor.getCount()= " + String.valueOf(cursor.getCount()));
        registerContentObserver(cursor, mObserver);
    }
    return cursor;
}

/**
 * Registers an observer to get notifications from the content provider
 * when the cursor needs to be refreshed.
 */
void registerContentObserver(Cursor cursor, ContentObserver observer) {
    cursor.registerContentObserver(mObserver);
}

/* Runs on the UI thread */
@Override
public void deliverResult(Cursor cursor) {
    Log.d("Gaurav","Inside SimpleCursorLoader - deliverResult");
    if (isReset()) {
        // An async query came in while the loader is stopped
        if (cursor != null) {
            cursor.close();
        }
        return;
    }
    Cursor oldCursor = mCursor;
    mCursor = cursor;

    if (isStarted()) {
        super.deliverResult(cursor);
    }

    if (oldCursor != null && oldCursor != cursor && !oldCursor.isClosed()) {
        oldCursor.close();
    }
}


/**
 * Starts an asynchronous load of the contacts list data. When the result is ready the callbacks
 * will be called on the UI thread. If a previous load has been completed and is still valid
 * the result may be passed to the callbacks immediately.
 *
 * Must be called from the UI thread
 */
@Override
protected void onStartLoading() {
    Log.d("Gaurav", "onStartLoading");
    if (mCursor != null) {
        deliverResult(mCursor);
    }
    if (takeContentChanged() || mCursor == null) {
        forceLoad();
    }
}

/**
 * Must be called from the UI thread
 */
@Override
protected void onStopLoading() {
    // Attempt to cancel the current load task if possible.
    cancelLoad();
}

@Override
public void onCanceled(Cursor cursor) {
    if (cursor != null && !cursor.isClosed()) {
        cursor.close();
    }
}

@Override
protected void onReset() {
    super.onReset();

    // Ensure the loader is stopped
    onStopLoading();

    if (mCursor != null && !mCursor.isClosed()) {
        mCursor.close();
    }
    mCursor = null;
}

}

CursorLoader 在带有自定义适配器的 ListFragment 中工作，该适配器扩展了 SimpleCursor Adapter 并在构造函数中传递 FLAG_REGISTER_CONTENT_OBSERVER，但是当列表中使用的响应更改基础数据时，光标会发生变化。

Answer 1

我遇到了同样的问题，尽管我使用的实现与您不同。我能够通过将通知 URI 明确声明为不太具体的内容来纠正我的问题。我确定我的代码还有其他问题导致我需要这样做，但它解决了我的问题。因此，我的内容提供程序中的光标查询来自：

@Override
public Cursor query(Uri uri, String[] projection, String selection, String[] selectionArgs,  String sortOrder) {

................
................
................

Cursor cursor = queryBuilder.query(mDB.getReadableDatabase(),
                projection, selection, selectionArgs, null, null, sortOrder);
                cursor.setNotificationUri(getContext().getContentResolver(), uri);
cursor.setNotificationUri(getContext().getContentResolver(), uri;)

到

@Override
public Cursor query(Uri uri, String[] projection, String selection, String[] selectionArgs,  String sortOrder) {

................
................
................

Cursor cursor = queryBuilder.query(mDB.getReadableDatabase(),
                projection, selection, selectionArgs, null, null, sortOrder);
                cursor.setNotificationUri(getContext().getContentResolver(), uri);
cursor.setNotificationUri(getContext().getContentResolver(), MYURI;)

其中 MYURI 是 URI 类型的变量，我知道它将涵盖我正在观看的所有内容。

希望这对某人有所帮助。

Answer 2

你需要重写转储方法。

@Override
    public void dump(String prefix, FileDescriptor fd, PrintWriter writer, String[] args) {
        super.dump(prefix, fd, writer, args);
        writer.print(prefix); writer.print("mTable="); writer.println(mTable);
        writer.print(prefix); writer.print("mDB=");writer.println(mDb);
        writer.print(prefix); writer.print("mProjection=");
                writer.println(Arrays.toString(mProjection));
        writer.print(prefix); writer.print("mSelection="); writer.println(mSelection);
        writer.print(prefix); writer.print("mSelectionArgs=");
                writer.println(Arrays.toString(mSelectionArgs));
        writer.print(prefix); writer.print("mSortOrder="); writer.println(mSortOrder);
        writer.print(prefix); writer.print("mCursor="); writer.println(mCursor);
        writer.print(prefix); writer.print("mContentChanged="); writer.println(mContentChanged);
    }