SELECT name FROM registration_data WHERE email ='{login }'，conn）;
var reader = cmd.ExecuteReader（）;
while（reader.Read（））labelWelcome.Text = reader [0] .ToString（）;
}

最后
{
conn.Close（）;
}
}
}

"SELECT name FROM registration_data WHERE email = '{login}'", conn); var reader = cmd.ExecuteReader(); while (reader.Read()) labelWelcome.Text = reader[0].ToString(); } finally { conn.Close(); } } }

不要 - 将用户控件的内部工作暴露给外界。

相反，请看这里：传输信息两种表格之间，第1部分：父母与子女 [ ^ ] - 它专注于表单，但控件的原则（甚至代码）完全相同（因为Form派生自Control）

Don't - that exposes the internal workings of the user control to the outside world.
Instead, see here: Transferring information between two forms, Part 1: Parent to Child[^] - it focusses on forms, but the principles (and even the code) are exactly the same for controls (because Form is derived from Control)