在調用Read（）之前訪問字段的嘗試無效（）

我收到錯誤：在調用Read（） at之前無效嘗試訪問字段：string result = Reader.GetString（0）;在調用Read（）之前訪問字段的嘗試無效（）

我不完全知道該怎麼做或什麼是錯，雖然

internal int GetCharGuidByName(string charactername, MySqlConnection connection) 
{ 
    MySqlCommand command = connection.CreateCommand(); 
    MySqlDataReader Reader; 
    command.CommandText = "SELECT guid FROM characters WHERE name=\""+charactername+"\";"; 
    // Initialize MySQL Reader 
    Reader = command.ExecuteReader(); 
    Reader.Read(); 
    string result = Reader.GetString(0); 
    // If the character doesn't exist or isn't entered, return 0 
    int charguid = 0; 
    if (result != String.Empty) 
    { 
     charguid = Convert.ToInt32(result); 
    } 
    return charguid; 
}

來源

2012-07-13 user1071461

你有沒有打開asigning讀者Command.ExecuteReader卻方法實施前的連接？並將Reader.Read（）更改爲if（Reader.Read（））{...}，並且如果沒有要讀取的結果，代碼將不會進入if語句。 – 2012-07-13 19:14:40

是的，連接是打開的，也試圖在這個函數內創建一個連接（不使用函數接收到的連接）並打開它，它也是一樣的 – user1071461 2012-07-13 19:16:18

更改代碼：

Reader = command.ExecuteReader(); 
int charguid = 0; 
if(Reader.Read()) 
{ 
    if(Reader[0] != DBNull.Value) 
    { 
     if(int.TryParse(Reader[0].ToString(), out charguid)) 
     { 
     //value read and is an integer! 
     } 
    } 
} 
return charguid;

來源

2012-07-13 19:19:46

我得到兩個錯誤：最好的重載方法匹配'int .Parse（string，System.IFormatProvider）'有一些無效參數，參數2：不能從'out int'轉換爲'System.IFormatProvider'從此代碼 – user1071461 2012-07-13 19:25:25

更改爲代碼。 – 2012-07-13 19:28:40

真棒，非常感謝，它的作品^^ – user1071461 2012-07-13 19:30:35

您應該使用的，而不是的ExecuteReader

ExecuteSaclar returns the first column of the first row in the result set, or a null reference

ExecuteReader will return as resultset which you have to then iterate to read

的ExecuteScalar所以看着你的代碼，你只需要結果集的第一列

internal int GetCharGuidByName(string charactername, MySqlConnection connection) 
{ 
    int charguid = 0; 

    using(MySqlCommand command = connection.CreateCommand()) 
    { 
     command.CommandText = "SELECT guid FROM characters WHERE name=\""+charactername+"\";"; 
     object obj = command.ExecuteScalar(); 
     if (obj != null && obj != DBNull.Value) 
     { 
     charguid = Convert.ToInt32(obj); 
     } 
    } 

     return charguid; 
}

來源

2012-07-13 19:48:14 HatSoft

  openConnection() 

      sql = "SELECT last, first, emp_type, active FROM employee INNER JOIN account ON employee.emp_id = account.emp_id WHERE employee.emp_id = '" & AtxtEmpID.Text & "'" 

      command = New MySqlCommand(sql, mySqlConnection) 

      reader = command.ExecuteReader 

      reader.Read() 

      AtxtEmpName.Text = reader.Item(0) & ", " & reader.Item(1) 

      closeConn()

有保存問題

來源

2016-03-29 05:55:02 LesDanThree

在調用Read（）之前訪問字段的嘗試無效（）

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