java - 如何在Android中的SQLite数据库中查找TEXT或VARCHAR类型的特定列占用的内存(大小)？

Question

我正在创建一个基于 Android 的笔记应用程序。我想在我的应用程序中向用户显示注释的大小。我知道文件和图像的大小可以在 sqlite 中轻松确定，但在这里我想获取标题和描述列占用的大小或内存，这些列是 TEXT 和 VARCHAR 数据类型(以字节为单位)。在我的案例中，数据库表中的一行代表一个注释。

我已经尝试了“Length”和“MAX”函数的所有可能的解决方案，但没有成功。 我已为此目的使用了准备好的 SQLite 语句，但无法获取具有特定 ID 的列的大小。 这是我的代码:

public class DataAdapterText
{
Context c;
    SQLiteDatabase db;
    DBHelperText helper;

    public DataAdapterText(Context c) {
        this.c = c;
        helper=new DBHelperText(c);
    }
public void getSize(int id)
{

    SQLiteStatement byteStatement = db.compileStatement("SELECT LENGTH(txtitle) FROM TX_Table WHERE tid='"+id+"'");
    long bytes = byteStatement.simpleQueryForLong();

    long kilobytes = 1024,
            megabytes = kilobytes * kilobytes,
            gigabytes = megabytes * kilobytes,
            terabytes = gigabytes * kilobytes;
if (bytes<kilobytes)
{
    Toast.makeText(c, bytes+" B", Toast.LENGTH_SHORT).show();
}
else if (bytes>=kilobytes && bytes<megabytes)
{
    Toast.makeText(c, bytes+" KB", Toast.LENGTH_SHORT).show();
}
else if (bytes>=megabytes && bytes<gigabytes)
{
    Toast.makeText(c, bytes+" MB", Toast.LENGTH_SHORT).show();
}
else if (bytes>=gigabytes && bytes<terabytes)
{
    Toast.makeText(c, bytes+" GB", Toast.LENGTH_SHORT).show();
}

}
}

public class TextNotes extends AppCompatActivity
{
   @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_text_notes);
 DataAdapterText dataAdapterText=new DataAdapterText(TextNotes.this);
        dataAdapterText.openDB();
        dataAdapterText.getSize(Id);//here Id is the ID of specific item when clicked by the user and is coming from the Recycler adapter. No issue with this ID!
        dataAdapterText.closeDB();
}

如果上面的 SELECT 语句中没有 WHERE 子句，则此代码运行时不会出错。但由于我想要具有特定 ID 的列的长度，所以我需要 WHERE 子句，但它给出了 WHERE 子句的错误。 如果有其他方法可以解决这个问题并获取笔记的大小，请指导我。 这是 logcat 错误:

2019-05-18 14:19:25.893 13286-13286/com.example.unifiednotesnew E/asset: AssetManager::addSystemOverlays delete oidmap
2019-05-18 14:19:39.943 13286-13286/com.example.unifiednotesnew E/AndroidRuntime: FATAL EXCEPTION: main
    Process: com.example.unifiednotesnew, PID: 13286
    java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.unifiednotesnew/com.example.unifiednotesnew.TextNotes}: android.database.sqlite.SQLiteDoneException
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2750)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2811)
        at android.app.ActivityThread.-wrap12(ActivityThread.java)
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1528)
        at android.os.Handler.dispatchMessage(Handler.java:102)
        at android.os.Looper.loop(Looper.java:154)
        at android.app.ActivityThread.main(ActivityThread.java:6316)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:872)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:762)
     Caused by: android.database.sqlite.SQLiteDoneException
        at android.database.sqlite.SQLiteConnection.nativeExecuteForLong(Native Method)
        at android.database.sqlite.SQLiteConnection.executeForLong(SQLiteConnection.java:604)
        at android.database.sqlite.SQLiteSession.executeForLong(SQLiteSession.java:790)
        at android.database.sqlite.SQLiteStatement.simpleQueryForLong(SQLiteStatement.java:107)
        at com.example.unifiednotesnew.Adapter.DataAdapterText.getSize(DataAdapterText.java:193)
        at com.example.unifiednotesnew.TextNotes.onCreate(TextNotes.java:125)
        at android.app.Activity.performCreate(Activity.java:6757)
        at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1119)
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2703)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2811) 
        at android.app.ActivityThread.-wrap12(ActivityThread.java) 
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1528) 
        at android.os.Handler.dispatchMessage(Handler.java:102) 
        at android.os.Looper.loop(Looper.java:154) 
        at android.app.ActivityThread.main(ActivityThread.java:6316) 
        at java.lang.reflect.Method.invoke(Native Method) 
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:872) 
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:762) 

Answer 1

问题

您的问题是没有选择任何行，并且没有可返回的值。

那就是:-

SQLiteDoneException

An exception that indicates that the SQLite program is done. Thrown when an operation that expects a row (such as SQLiteStatement#simpleQueryForString or SQLiteStatement#simpleQueryForLong) does not get one.

修复

您可以捕获异常，例如

........
SQLiteStatement byteStatement = db.compileStatement("SELECT LENGTH(txtitle) FROM TX_Table WHERE tid='"+id+"'");
long bytes = 0;
try {
    bytes = byteStatement.simpleQueryForLong();
} catch (SQLiteDoneException e) {
    
}

long kilobytes = 1024,
........

或通过游标获取值，例如类似的东西:-

public long getColumnLengthById(String table, String column, long id, String idcolumn) {
    long rv = 0;
    String rv_column = "LEN";
    String[] columns = new String[]{"length(" + column + ") AS " + rv_column};
    String whereclause = idcolumn + "=?";
    String[] whereargs = new String[]{String.valueOf(id)};
    SQLiteDatabase db = this.getWritableDatabase();
    Cursor csr = db.query(table,columns,whereclause,whereargs,null,null,null);
    while (csr.moveToNext()) {
        rv = rv + csr.getLong(csr.getColumnIndex(rv_column));
    }
    csr.close();
    return rv;
}