问题1-找不到列

Question

我正在尝试从SQLite数据库中检索图像，但是CURSOR总是没有结果。如果我尝试选择没有图像列的图片，那么效果很好。

 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;
}

因为CURSOR没有结果，所以它返回“ null”。 INSERT方法有效。

Answer 1

有两个可能的问题，这两个问题都会导致异常，可以通过查看日志来确定。

问题1-找不到列

第一个常见问题是通过修改 onCreate 方法使用的代码将一列添加到表中。

例如您可能已经更改了表创建SQL，以使其包含定义了 COLUNA_IMG 列，因为该应用程序已运行。

onCreate 方法仅在第一次创建数据库时运行一次。它不会在每次运行App或每次创建DatabaseHelper类的实例时运行。

可以通过查看日志来确定此问题，在这种情况下，您可以找到类似于：-

的内容。

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)

请注意，如果您使用的是Android Studio，则会在aaa.so54989458.DBHelper.selecionarLivro（DBHelper.java:70）中突出显示该行，并通过单击在链接上，您可以转到在代码中引发异常的代码。

（请注意，发生错误的方法是您的 selecionarLivro 方法，其他方面（如类和程序包名称）将取决于您的代码）。

解决问题1

解决上述问题的方法是执行以下一项操作：-

（通过“设置”）删除/清除应用程序的数据。

卸载应用

然后，假设代码正确，则重新运行该应用程序。

问题2-图片太大。

图像不是用于存储在数据库中的理想候选对象，而是最好存储一些指示要使用的图像的内容（例如，图像的路径）。图像本身由字节组成，通常是非常大量的字节。虽然SQLite可以容纳相当大的图像。

将数据提取到游标中的android SDK实现更具限制性。

Cursor实际上是一个缓冲区，用于保存整个数据的部分快照。基础快照（游标窗口）在Android SDK中限制为2M，并且至少必须能够容纳一行。如果您拥有2M或更大的图像，则可以保证您将失败。如果图像大于0.5M，您很可能会失败或出现问题。

一个错误示例，即使它已成功存储在数据库中，但对于“游标窗口”而言，图像太大：-

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)

请注意，前三行用于图像可以容纳的前几行（基本上，消息是说CursorWindow未满，对不起无法再获得更多行。）

解决问题2

没有简单的解决方法，除非您可以将图像尺寸减小到可接受/可控制的尺寸。

推荐的方法是将图像存储在其他位置，然后将路径或路径的一部分存储在数据库中。

Here's一个示例，该示例结合使用以下方法：将大于100k的图像路径存储在数据库中，如果数据库中的图像小于等于100k，则存储图像（效率更高）。

无法从SQLite数据库选择图像（Android）

1 个答案:

问题1-找不到列

解决问题1

问题2-图片太大。

解决问题2