我正在尝试从SQLite数据库中检索图像，但CURSOR始终没有结果。如果我尝试选择没有图像列，它可以正常工作。
Livro selecionarLivro(String titulo, String autor)
{
SQLiteDatabase db = this.getReadableDatabase();
String[] dados = new String[2];
dados[0] = titulo;
dados[1] = autor;
Livro livro1 = null;
Cursor cursor;
String[] campos = {COLUNA_CODIGO, COLUNA_TITULO, COLUNA_AUTOR, COLUNA_IMG};
cursor = db.query(TABELA_LIVROS, campos, COLUNA_TITULO + "=? AND " + COLUNA_AUTOR + "=?", dados, null, null, null, null);
if(cursor.moveToNext()){
livro1 = new Livro();
livro1.setTitulo(cursor.getString(cursor.getColumnIndex(COLUNA_TITULO)));
livro1.setAutor(cursor.getString(cursor.getColumnIndex(COLUNA_AUTOR)));
livro1.setImgFile(cursor.getBlob(cursor.getColumnIndex(COLUNA_IMG)));
}
db.close();
return livro1;
}
它返回“null”，因为CURSOR没有结果。 INSERT方法正在运行。
有两个可能的问题都会导致异常，可以通过查看日志来确定。
第一个常见问题是通过修改onCreate方法使用的代码将列添加到表中。
首次创建数据库时，onCreate方法仅运行一次。每次运行App或每次创建DatabaseHelper类的实例时都不会运行它。
这个问题可以通过查看日志来确定，在这种情况下你可以找到类似的东西： -
2019-03-05 11:17:10.446 8872-8872/aaa.so54989458 E/SQLiteLog: (1) no such column: img
2019-03-05 11:17:10.447 8872-8872/aaa.so54989458 D/AndroidRuntime: Shutting down VM
2019-03-05 11:17:10.455 8872-8872/aaa.so54989458 E/AndroidRuntime: FATAL EXCEPTION: main
Process: aaa.so54989458, PID: 8872
android.database.sqlite.SQLiteException: no such column: img (code 1 SQLITE_ERROR): , while compiling: SELECT codigo, titulo, autor, img FROM livros WHERE titulo=? AND autor=?
at android.database.sqlite.SQLiteConnection.nativePrepareStatement(Native Method)
at android.database.sqlite.SQLiteConnection.acquirePreparedStatement(SQLiteConnection.java:903)
at android.database.sqlite.SQLiteConnection.prepare(SQLiteConnection.java:514)
at android.database.sqlite.SQLiteSession.prepare(SQLiteSession.java:588)
at android.database.sqlite.SQLiteProgram.<init>(SQLiteProgram.java:58)
at android.database.sqlite.SQLiteQuery.<init>(SQLiteQuery.java:37)
at android.database.sqlite.SQLiteDirectCursorDriver.query(SQLiteDirectCursorDriver.java:46)
at android.database.sqlite.SQLiteDatabase.rawQueryWithFactory(SQLiteDatabase.java:1408)
at android.database.sqlite.SQLiteDatabase.queryWithFactory(SQLiteDatabase.java:1255)
at android.database.sqlite.SQLiteDatabase.query(SQLiteDatabase.java:1126)
at android.database.sqlite.SQLiteDatabase.query(SQLiteDatabase.java:1332)
at aaa.so54989458.DBHelper.selecionarLivro(DBHelper.java:70)
at aaa.so54989458.MainActivity$2.onItemClick(MainActivity.java:78)
at android.widget.AdapterView.performItemClick(AdapterView.java:318)
at android.widget.AbsListView.performItemClick(AbsListView.java:1159)
at android.widget.AbsListView$PerformClick.run(AbsListView.java:3136)
at android.widget.AbsListView$3.run(AbsListView.java:4052)
at android.os.Handler.handleCallback(Handler.java:873)
at android.os.Handler.dispatchMessage(Handler.java:99)
at android.os.Looper.loop(Looper.java:193)
at android.app.ActivityThread.main(ActivityThread.java:6669)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:858)
针对上述问题的解决方法是执行以下操作之一： -
然后，假设代码正确，重新运行应用程序。
图像不是存储在数据库中的理想候选者，而是存储指示要使用的图像的东西（例如，图像的路径）更好。图像本身由字节组成，通常是非常大的字节数。虽然SQLite可以容纳相当大的图像。
将数据提取到Cursor的android SDK实现更具限制性。
Cursor实际上是一个缓冲区，它保存整个数据的部分快照。底层快照（Cursor Window）在Android SDK中限制为2M，并且至少必须能够容纳一行。如果您的图像长度为2M或更多，则可以确保失败。如果图像大于0.5M，则很可能会出现故障或问题。
图像对于光标窗口来说太大的错误示例，即使它已成功存储在数据库中，也是： -
2019-03-05 11:33:46.878 9059-9059/aaa.so54989458 W/CursorWindow: Window is full: requested allocation 2097152 bytes, free space 1789213 bytes, window size 2097152 bytes
2019-03-05 11:33:46.886 9059-9059/aaa.so54989458 W/CursorWindow: Window is full: requested allocation 2097152 bytes, free space 1983933 bytes, window size 2097152 bytes
2019-03-05 11:33:46.886 9059-9059/aaa.so54989458 W/CursorWindow: Window is full: requested allocation 2097152 bytes, free space 2096653 bytes, window size 2097152 bytes
2019-03-05 11:33:46.887 9059-9059/aaa.so54989458 E/SQLiteQuery: exception: Row too big to fit into CursorWindow requiredPos=3, totalRows=4; query: SELECT * FROM livros
2019-03-05 11:33:46.887 9059-9059/aaa.so54989458 D/AndroidRuntime: Shutting down VM
2019-03-05 11:33:46.895 9059-9059/aaa.so54989458 E/AndroidRuntime: FATAL EXCEPTION: main
Process: aaa.so54989458, PID: 9059
android.database.sqlite.SQLiteBlobTooBigException: Row too big to fit into CursorWindow requiredPos=3, totalRows=4
at android.database.sqlite.SQLiteConnection.nativeExecuteForCursorWindow(Native Method)
at android.database.sqlite.SQLiteConnection.executeForCursorWindow(SQLiteConnection.java:859)
at android.database.sqlite.SQLiteSession.executeForCursorWindow(SQLiteSession.java:836)
at android.database.sqlite.SQLiteQuery.fillWindow(SQLiteQuery.java:62)
at android.database.sqlite.SQLiteCursor.fillWindow(SQLiteCursor.java:157)
at android.database.sqlite.SQLiteCursor.onMove(SQLiteCursor.java:128)
at android.database.AbstractCursor.moveToPosition(AbstractCursor.java:237)
at android.widget.CursorAdapter.getItemId(CursorAdapter.java:258)
at android.widget.AbsListView$RecycleBin.retrieveFromScrap(AbsListView.java:7105)
at android.widget.AbsListView$RecycleBin.getScrapView(AbsListView.java:6816)
at android.widget.AbsListView.obtainView(AbsListView.java:2365)
at android.widget.ListView.measureHeightOfChildren(ListView.java:1408)
at android.widget.ListView.onMeasure(ListView.java:1315)
at android.view.View.measure(View.java:23169)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6749)
at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1535)
at android.widget.LinearLayout.measureVertical(LinearLayout.java:825)
at android.widget.LinearLayout.onMeasure(LinearLayout.java:704)
at android.view.View.measure(View.java:23169)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6749)
at android.widget.FrameLayout.onMeasure(FrameLayout.java:185)
at android.support.v7.widget.ContentFrameLayout.onMeasure(ContentFrameLayout.java:143)
at android.view.View.measure(View.java:23169)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6749)
at android.support.v7.widget.ActionBarOverlayLayout.onMeasure(ActionBarOverlayLayout.java:401)
at android.view.View.measure(View.java:23169)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6749)
at android.widget.FrameLayout.onMeasure(FrameLayout.java:185)
at android.view.View.measure(View.java:23169)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6749)
at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1535)
at android.widget.LinearLayout.measureVertical(LinearLayout.java:825)
at android.widget.LinearLayout.onMeasure(LinearLayout.java:704)
at android.view.View.measure(View.java:23169)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6749)
at android.widget.FrameLayout.onMeasure(FrameLayout.java:185)
at com.android.internal.policy.DecorView.onMeasure(DecorView.java:716)
at android.view.View.measure(View.java:23169)
at android.view.ViewRootImpl.performMeasure(ViewRootImpl.java:2718)
at android.view.ViewRootImpl.measureHierarchy(ViewRootImpl.java:1572)
at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1855)
at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1460)
at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:7183)
at android.view.Choreographer$CallbackRecord.run(Choreographer.java:949)
at android.view.Choreographer.doCallbacks(Choreographer.java:761)
at android.view.Choreographer.doFrame(Choreographer.java:696)
at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:935)
at android.os.Handler.handleCallback(Handler.java:873)
at android.os.Handler.dispatchMessage(Handler.java:99)
at android.os.Looper.loop(Looper.java:193)
at android.app.ActivityThread.main(ActivityThread.java:6669)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:858)
除非您可以将图像的大小减小到可接受/可管理的大小，否则没有简单的修复。
建议的方法是将图像存储在别处，然后将路径或其中的一部分存储在数据库中。