"Make sure Cursor is initialized before accessing data from it" Android

Question

我知道这个问题以前被问过很多次，但在这种情况下是不同的，因为错误仅在尝试将图像保存到数据库时发生，而其他问题不涉及图像。有的话请评论link.

首先，我只发布我认为必要的代码，所以如果我遗漏了某些代码或任何内容，请告诉我。我有一个 note-taking 应用程序，它存储 2 个不同的 EditText 字段作为注释标题和注释 body。那很好用。我尝试添加功能以从 SQLite 数据库添加、存储和检索图像。这是我的 EditNoteActivity class 中的代码，它在用户完成编辑笔记并按下后退按钮转到 MainActivity class.

后的 "store" 操作期间运行

private void updateNote(String noteText, String titleText) {
        Log.d("Img", "updateNote");
        ContentValues values = new ContentValues();
        ImageView img = (ImageView) findViewById(R.id.imageView);

        byte[] data;
        if (img.getDrawable() != null) {
            Log.d("Img", "updateNote ----- image here");
            Bitmap bitmap = ((BitmapDrawable)img.getDrawable()).getBitmap();
//        data = getBitmapAsByteArray(bitmap);
            data = DbBitmapUtility.getBytes(bitmap);
        } else {
            Log.d("Img", "updateNote ----- image not here");
            data = null;
        }
        values.put(DBOpenHelper.NOTE_IMAGE, data);
        values.put(DBOpenHelper.NOTE_BODY, noteText);
        values.put(DBOpenHelper.NOTE_TITLE, titleText);
        // reusing noteFilter value to make sure you're only updating 1 selected row
        getContentResolver().update(NoteProvider.CONTENT_URI, values, noteFilter, null);
        Toast.makeText(this, R.string.note_updated, Toast.LENGTH_SHORT).show();
        setResult(RESULT_OK);   // send message to MainActivity saying something has changed, update content in list
    }

如果我不向 ImageView 添加图像，那么我可以毫无问题地保存笔记。但是如果我添加图像然后尝试返回 MainActivity，程序会在以下行崩溃：

@Override
public void onLoadFinished(Loader<Cursor> loader, Cursor data) {
    cursorAdapter.swapCursor(data);    // crashes here
}

它也在 class 声明中崩溃：

public class MainActivity extends AppCompatActivity

因为我经常使用 Log.d，它确实在 logcat 中说了以下内容：

updateNote updateNote ----- image here

如果您遵循 updateNote 方法中的代码，它应该是这样。这是 DbBitmapUtility class 中的 getBytes 方法，我用它来获取字节数组以将图像存储为 BLOB：

// convert from bitmap to byte array
public static byte[] getBytes(Bitmap bitmap) {
    ByteArrayOutputStream stream = new ByteArrayOutputStream();
    bitmap.compress(Bitmap.CompressFormat.PNG, 0, stream);
    return stream.toByteArray();
}

最后是我的数据库设置：

public static final String TABLE_NOTES = "notes";
public static final String NOTE_ID = "_id";
public static final String NOTE_TITLE = "noteTitle";
public static final String NOTE_BODY = "noteBody";
public static final String NOTE_IMAGE = "noteImage";
public static final String NOTE_CREATED = "noteCreated";

public static final String[] ALL_COLUMNS =
        {NOTE_ID, NOTE_TITLE, NOTE_BODY, NOTE_IMAGE, NOTE_CREATED};
// SQL to create table
private static final String TABLE_CREATE =
        "CREATE TABLE " + TABLE_NOTES + " (" +
                NOTE_ID + " INTEGER PRIMARY KEY AUTOINCREMENT, " +
                NOTE_TITLE + " TEXT, " +
                NOTE_BODY + " TEXT, " +
                NOTE_IMAGE + " BLOB, " +
                NOTE_CREATED + " TEXT default CURRENT_TIMESTAMP" +
                ")";

错误如下：

E/AndroidRuntime: FATAL EXCEPTION: main Process: com.beauty.comp_eng.mynote, PID: 16435 java.lang.IllegalStateException: Couldn't read row 0, col 0 from CursorWindow. Make sure the Cursor is initialized correctly before accessing data from it. at android.database.CursorWindow.nativeGetLong(Native Method) at android.database.CursorWindow.getLong(CursorWindow.java:511) at android.database.AbstractWindowedCursor.getLong(AbstractWindowedCursor.java:75) at android.database.CursorWrapper.getLong(CursorWrapper.java:127) at android.widget.CursorAdapter.getItemId(CursorAdapter.java:259) at android.widget.AdapterView.rememberSyncState(AdapterView.java:1243) at android.widget.AdapterView$AdapterDataSetObserver.onChanged(AdapterView.java:830) at android.widget.AbsListView$AdapterDataSetObserver.onChanged(AbsListView.java:6470) at android.database.DataSetObservable.notifyChanged(DataSetObservable.java:37) at android.widget.BaseAdapter.notifyDataSetChanged(BaseAdapter.java:50) at android.widget.CursorAdapter.swapCursor(CursorAdapter.java:381) at com.beauty.comp_eng.mynote.MainActivity.onLoadFinished(MainActivity.java:200) at com.beauty.comp_eng.mynote.MainActivity.onLoadFinished(MainActivity.java:25) at android.support.v4.app.LoaderManagerImpl$LoaderInfo.callOnLoadFinished(LoaderManager.java:479) at android.support.v4.app.LoaderManagerImpl$LoaderInfo.onLoadComplete(LoaderManager.java:447) at android.support.v4.content.Loader.deliverResult(Loader.java:126) at android.support.v4.content.CursorLoader.deliverResult(CursorLoader.java:105) at android.support.v4.content.CursorLoader.deliverResult(CursorLoader.java:37) at android.support.v4.content.AsyncTaskLoader.dispatchOnLoadComplete(AsyncTaskLoader.java:249) at android.support.v4.content.AsyncTaskLoader$LoadTask.onPostExecute(AsyncTaskLoader.java:77) at android.support.v4.content.ModernAsyncTask.finish(ModernAsyncTask.java:466) at android.support.v4.content.ModernAsyncTask.access0(ModernAsyncTask.java:48) at android.support.v4.content.ModernAsyncTask$InternalHandler.handleMessage(ModernAsyncTask.java:483) at android.os.Handler.dispatchMessage(Handler.java:102) at android.os.Looper.loop(Looper.java:148) at android.app.ActivityThread.main(ActivityThread.java:5525) at java.lang.reflect.Method.invoke(Native Method) at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:730) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:620)

我以为我正确地存储了图像，因为我发现他们在许多其他 Whosebug 答案中都是这样做的，但它不起作用。我注意到它说

Couldn't read row 0, col 0 from CursorWindow. Make sure the Cursor is initialized correctly before accessing data from it.

如果数据库中已有无图片的普通笔记，为什么没有返回记录？

Answer 1

Android sqlite 游标有一个固定大小的内部缓冲区，称为 CursorWindow，在大多数配置下为 2MB。尝试在游标行中移动更多数据将不起作用。

不要在 Android sqlite 数据库中存储图像数据或任何其他大数据。相反，将图像存储到文件系统并将文件路径存储在数据库中。

"Make sure Cursor is initialized before accessing data from it" Android

"Make sure Cursor is initialized before accessing data from it" Android

sqlite

android

blob