winform 中的 combox 问题 急急急~~~~~

Question

是这样的 我有一个确定键（btnsure） 用户名写下去了 按确定 combox里的选项就跳出来了 我又多按了几下确定键 结果combox里多出了好多的选项而且是重复的  我的combox里的选项原本只有两个 怎么能让他不重复呢？
        private void btnSure_Click(object sender, EventArgs e)
        {
            string sql = string.Format("select count(*) from protect where UserName='{0}'",this.tbName.Text);
            SqlCommand sqlcom = new SqlCommand(sql, DBhelper.connection);
            DBhelper.connection.Open();
            int count = int.Parse(sqlcom.ExecuteScalar().ToString());
            DBhelper.connection.Close();
            if (count > 0 )
            {                string sqlu = string.Format("select * from protect where UserName='{0}'", this.tbName.Text);
                SqlCommand sqlc = new SqlCommand(sqlu, DBhelper.connection);
                DBhelper.connection.Open();
                SqlDataReader reader = sqlc.ExecuteReader();
                if (reader.Read())
                {
                    
                    cmbQuestion.Items.Add(reader["Question1"]);
                    cmbQuestion.Items.Add(reader["Question2"]);
                
                }
                DBhelper.connection.Close();
            }
            else
            {
                MessageBox.Show("该用户不存在!");
            }

Answer 1

每次点击的时候清空combox中的内容

Answer 2

private void btnSure_Click(object sender, EventArgs e)
  {
  string sql = string.Format("select count(*) from protect where UserName='{0}'",this.tbName.Text);
  SqlCommand sqlcom = new SqlCommand(sql, DBhelper.connection);
  DBhelper.connection.Open();
  int count = int.Parse(sqlcom.ExecuteScalar().ToString());
  DBhelper.connection.Close();
  if (count > 0 )
  {  string sqlu = string.Format("select * from protect where UserName='{0}'", this.tbName.Text);
  SqlCommand sqlc = new SqlCommand(sqlu, DBhelper.connection);
  DBhelper.connection.Open();
  SqlDataReader reader = sqlc.ExecuteReader();
  if (reader.Read())
  {
   cmbQuestion.Items.Clear(); 
  cmbQuestion.Items.Add(reader["Question1"]);
  cmbQuestion.Items.Add(reader["Question2"]);
    
  }
  DBhelper.connection.Close();
  }
  else
  {
  MessageBox.Show("该用户不存在!");
  }

Answer 3

要这样 
private void btnSure_Click(object sender, EventArgs e)
  {
if(cmbQuestion.Items.Count>0)
{
    cmbQuestion.Items.Clear();
}
  string sql = string.Format("select count(*) from protect where UserName='{0}'",this.tbName.Text);
  SqlCommand sqlcom = new SqlCommand(sql, DBhelper.connection);
  DBhelper.connection.Open();
  int count = int.Parse(sqlcom.ExecuteScalar().ToString());
  DBhelper.connection.Close();
  if (count > 0 )
  {  string sqlu = string.Format("select * from protect where UserName='{0}'", this.tbName.Text);
  SqlCommand sqlc = new SqlCommand(sqlu, DBhelper.connection);
  DBhelper.connection.Open();
  SqlDataReader reader = sqlc.ExecuteReader();
  if (reader.Read())
  {  cmbQuestion.Items.Add(reader["Question1"]);
  cmbQuestion.Items.Add(reader["Question2"]);
   
  }
  DBhelper.connection.Close();
  }
  else
  {
  MessageBox.Show("该用户不存在!");
  }

Answer 4

 if (reader.Read())
  {
cmbQuestion.Items.Clear(); 
  cmbQuestion.Items.Add(reader["Question1"]);
  cmbQuestion.Items.Add(reader["Question2"]);
    
  }

Answer 5

呵呵  大家说的都可以 但是怎么设置combox选项默认为Question1呢

Answer 6

你说的这个方法可以啊  再问一下怎么设置combox选项默认为Question1呢

Answer 7

ComboBox.Items.Contains(object value)
combobox.Text="指定的value";