Question

我正试图用下面的代码获取给定身份识别码的相应标题

public String get_Title(int id){
        Cursor c = db.query(true, DATABASE_TABLE, new String[] {
                APP_TITLE,
                },
                KEY_ROWID + "="  + id,
                null,
                null,
                null,
                null,
                null);

                String Final = c.getString(0);

                return Final;

        }

我总是把指数导致的例外排除在外。光标的IM对光标不好, 所以如果有人能帮助我在这里。 S: S

Answer 1

您必须在 string final = c.get String(0) call c.moveToFirst () 或 c.moveToNext () 或 或或 /code> 之前,先隐含地定位于第一行 < / tring(0) < /code> 的位置,然后您才能将 Cursor 移动到第一行,然后从中获取数据。



<强度 > EDIT: 



<强>,所以它应该像这样: 

if (c.getCount()) { // if there is some data
   c.moveToFirst();
   String Final = c.getString(0);
}
else {
   Toast.makeText(YourActivityName.this, "No data found", Toast.LENGTH_SHORT).show();
}


所以您写道您在 Cursor  的小介绍中工作不好:


  If you execute any statement, always instance of Cursor class will be
  returned. It s version of a database cursor, it is used in many
  database systems.


Class Cursor have following few basic methods:



getCount() - to get how many rows is in actual cursor
moveToFirst(), moveToNext() etc. - for moving between rows
getColumnNames() - to get column  names
getColumnIndex() - to get the zero-based index for the given column
name...
getString(), getInt() etc. - to get data of requested column  index
requery() - once again execute cursor
close() - to release resources of cursor.
and next...


有关光标工作的更多信息,您可以找到 这里 

观 观 观

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