【发布时间】：2018-05-11 22:42:32
【问题描述】：
我的游标和数据库有问题，如果我使用 !cursor.isAfterLast() 一段时间，在实际非空行之后，我启动应用程序的次数与我启动应用程序的次数一样多（并放了一个行中的值）
这是我的代码：
public class DatabaseCreator extends SQLiteOpenHelper {
// Database Version
private static final int DATABASE_VERSION = 1;
// Database Name
private static final String DATABASE_NAME_WITH_EXTENSION = "drawinguess_local_database.db";
// Table Names
public static final String DB_TABLE = "image_bmp";
// column names
private static final String COLUMN_ID = "_id";
private static final String KEY_NAME = "image_title";
private static final String KEY_AUTHOR = "image_author";
private static final String KEY_IMAGE = "image_data";
// Table create statement
private static final String CREATE_TABLE_IMAGE = "CREATE TABLE " + DB_TABLE + "("+ COLUMN_ID + " integer primary key autoincrement, " + KEY_NAME + " TEXT," + KEY_AUTHOR + " TEXT," + KEY_IMAGE + " BLOB);";
public DatabaseCreator(Context context) {
super(context, DATABASE_NAME_WITH_EXTENSION, null, DATABASE_VERSION);
}
@Override
public void onCreate(SQLiteDatabase db) {
db.execSQL("DROP TABLE IF EXISTS " + DB_TABLE);
db.execSQL(CREATE_TABLE_IMAGE);
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
// on upgrade drop older tables
db.execSQL("DROP TABLE IF EXISTS " + DB_TABLE);
// create new table
onCreate(db);
}
public void addEntry(String title, String author, byte[] image) throws SQLiteException {
SQLiteDatabase database = this.getWritableDatabase();
ContentValues cv = new ContentValues();
cv.put(KEY_NAME, title);
cv.put(KEY_AUTHOR, author);
cv.put(KEY_IMAGE, image);
database.insert( DB_TABLE, null, cv );
}
public void addEntry(String title, byte[] image) throws SQLiteException {
SQLiteDatabase database = this.getWritableDatabase();
ContentValues cv = new ContentValues();
cv.put(KEY_NAME, title);
cv.put(KEY_IMAGE, image);
database.insert( DB_TABLE, null, cv );
}
public void addEntry(byte[] image) throws SQLiteException {
SQLiteDatabase database = this.getWritableDatabase();
ContentValues cv = new ContentValues();
cv.put(KEY_IMAGE, image);
database.insert( DB_TABLE, null, cv );
}
public void updateLastTitle(String title) throws SQLiteException{
SQLiteDatabase database = this.getWritableDatabase();
String strSQL;
//Cursor cursor = database.query(DATABASE_NAME, new String[]{"ID"}, null, null, null, null, null);
Cursor cursor = database.rawQuery("SELECT "+ COLUMN_ID +" FROM " + DB_TABLE, null);
cursor.moveToLast();
strSQL = "UPDATE " + DB_TABLE + " SET "+ KEY_NAME + " = \"" + title +"\" WHERE "+ COLUMN_ID +" = "+ cursor.getColumnCount();
database.execSQL(strSQL);
}
public List<TitledBitmap> getAllTitledBitmap() {
SQLiteDatabase database = this.getReadableDatabase();
List<TitledBitmap> titledBitmaps = new ArrayList<TitledBitmap>();
Cursor cursor = database.query(DB_TABLE, new String[]{"image_title", "image_data"}, null, null, null, null, null);
cursor.moveToFirst();
while (!cursor.isAfterLast()) {
System.out.println("This is the title : " + cursor.getString(0));
TitledBitmap titledBitmap = cursorToTitledBitmap(cursor);
titledBitmaps.add(titledBitmap);
cursor.moveToNext();
}
cursor.close();
return titledBitmaps;
}
private TitledBitmap cursorToTitledBitmap(Cursor cursor) {
TitledBitmap titledBitmap = new TitledBitmap();
titledBitmap.setTitle(cursor.getString(0));
titledBitmap.setByteArray(cursor.getBlob(1));
return titledBitmap;
}
}
问题出在 getAllTitledBitmap() 中，我猜，这要归功于 Syso 的输出：
I/System.out: This is the title : TheValueThatWorked
This is the title : null
This is the title : null
提前谢谢你 祝你有美好的一天
【问题讨论】：
-
数据库中标题的可能性为空，我看不出有什么明显的错误。
-
谢谢！我试图搜索原因，但我不知道，否则，我使用多个活动将数据写入数据库，但我只有最后一个条目工作，所有其他都是 null 我使用 DatabaseCreator db = new DatabaseCreator(this)我所有的活动，也许这搞砸了？
-
重新评论 “我在所有活动中都使用 DatabaseCreator db = new DatabaseCreator(this)，也许这搞砸了？”。不，这不会把事情搞砸，你应该这样做。
标签： android sql database sqlite loops