我在检查数据库中的“Administrator”文本后,尝试删除组合框项目列表中的“Administrator”文本,如果找到,则会只需从下拉列表菜单中删除即可。
现在,即使数据库中有“Administrator”文本,组合框仍然会将“Administrator”文本添加到项目列表中。< / p>
某处错了吗?
以下是我正在使用的代码:
public partial class Registration: Form
{
bool _isCheckedEmail = false;
void Registration_Load(object sender, EventArgs e)
{
ClearTextBoxes();
SystemManager.CheckType("Administrator");
if (SystemManager._isUsed != true)
{
this.comboBox1.Items.Add("Administrator");
}
this.comboBox1.Items.Add("Member");
this.comboBox1.SelectedIndex = 0;
SystemManager._isCheckedDisplayName = false;
_isCheckedEmail = false;
this.button1.Enabled = false;
this.button4.Enabled = false;
}
}
这是 “SystemManager” 类:
public class SystemManager
{
public static bool _isUsed = false;
public static void CheckType(string _value1)
{
using (OleDbConnection connection = new OleDbConnection(SystemManager.connectionString))
{
string query = "SELECT COUNT(*) FROM [Member] WHERE [UserType] = @UserType";
connection.Open();
using (OleDbCommand command = new OleDbCommand(query, connection))
{
command.Parameters.Add("@UserType", OleDbType.VarChar);
command.Parameters["@UserType"].Value = _value1;
using (OleDbDataReader reader = command.ExecuteReader())
{
while (reader.Read())
{
if (_count > 0)
{
_isUsed = true;
}
else
{
_isUsed = false;
}
}
reader.Close();
}
}
connection.Close();
}
}
}
这是数据库(我将其上传到保管箱):
谢谢。
答案 0 :(得分:1)
您可以通过reader[0]
引用结果对象。
using (OleDbDataReader reader = command.ExecuteReader())
{
while (reader.Read())
{
Integer.TryParse(reader[0].ToString(), _count);
if (_count > 0)
{
_isUsed = true;
}
else
{
_isUsed = false;
}
}
reader.Close();
}
使用OleDbDataReader.HasRows
属性检查类型是否存在。
http://msdn.microsoft.com/en-us/library/system.data.oledb.oledbdatareader.hasrows(v=vs.110).aspx
string query = "SELECT * FROM [Member] WHERE [UserType] = @UserType";
connection.Open();
using (OleDbCommand command = new OleDbCommand(query, connection))
{
command.Parameters.Add("@UserType", OleDbType.VarChar);
command.Parameters["@UserType"].Value = _value1;
using (OleDbDataReader reader = command.ExecuteReader())
{
while (reader.Read())
{
if (reader.HasRows)
{
_isUsed = true;
}
else
{
_isUsed = false;
}
}
reader.Close();
}
答案 1 :(得分:0)
以上是上述问题的解决方案:
void Registration_Load(object sender, EventArgs e)
{
SystemManager.ClearTextBoxes(this.Controls);
if (SystemManager.CheckType("Administrator") != true)
{
this.comboBox1.Items.Add("Administrator");
}
this.comboBox1.Items.Add("Member");
this.comboBox1.SelectedIndex = 0;
SystemManager._isCheckedDisplayName = false;
_isCheckedEmail = false;
this.button1.Enabled = false;
this.button4.Enabled = false;
}
public static bool CheckType(string _value1)
{
using (OleDbConnection connection = new OleDbConnection(SystemManager.connectionString))
{
string query = "SELECT COUNT(*) FROM [Member] WHERE [UserType] = @UserType";
connection.Open();
using (OleDbCommand command = new OleDbCommand(query, connection))
{
command.Parameters.Add("@UserType", OleDbType.VarChar);
command.Parameters["@UserType"].Value = _value1;
_count = (int)command.ExecuteScalar();
connection.Close();
}
}
return _count > 0;
}