错误：位置 0 没有行如何修复

Question

This image is where after user login, they will be able to see their account details.

This image is another small form that allows the user to change the username.

Currently, the error is when after changing the username. When it directed back to a page in image 1, it crashes.

public void showdata()
{
    cmd.CommandText = "Select * from Registration where Username='" + Session["user"] + "'";
    cmd.Connection = con;
    sda.SelectCommand = cmd;
    sda.Fill(ds);

    lblUsername.Text = ds.Tables[0].Rows[0]["Username"].ToString();// error occur at here. 
    lblEmail.Text = ds.Tables[0].Rows[0]["Email"].ToString();
    lblName.Text = ds.Tables[0].Rows[0]["Fullname"].ToString();
    lblContact.Text = ds.Tables[0].Rows[0]["Contactnumber"].ToString();
    lblPassword.Text = ds.Tables[0].Rows[0]["Password"].ToString();
}

I do not understand this error. The error is there is no row at position 0.

Answer 1

There is no row at position 0 - that means your result set is empty and you need to check count before access any row.

if (ds.Tables == null || ds.Tables.Count == 0 || ds.Tables[0].Rows.Count == 0) {
    // Throw the error or retrun the code 
}

Note:

• Need to handle null every time before getting value from Session. You can create a custom class for handling all sessions for that. Refer this link for Custom Class

• Before getting value from row also need to handle NULL. like use below method

  public static T GetValueFromDataRow<T>(this DataRow row, string columnName) { if (row.Table.Columns.Contains(columnName) && (object)row[columnName] != DBNull.Value) { return (T)row[columnName]; } return default; }

Answer 2

You need to verify that rows exist before attempting to get data from them.

if (ds.Tables[0].Rows.Count > 0){
    // Fetch the data... 
}
else
{
    // Handle missing data or show some friendly message 
}

Answer 3

在 Change() 函数中，没有代码更新 Session["user"] 中的用户名，因此可能发生的情况是您的 SELECT 命令仍在使用以前的用户名，因此返回 0 行。

Answer 4

In showdata() function is you are sending Session["user"] as username value, which you have not set in Change() function .

So, in Change() function,to get the updated value first set

Session["user"]= txtuserchange.Text

Please check and confirm.

Answer 5

请确保您的 Session["user"] 具有有效数据和查询返回列表或注册对象。