ConnectionString 属性尚未初始化
public partial class User : Form
{


public User()
{
InitializeComponent();

}

public DataSet ds = new DataSet();
SqlDataAdapter sda1 = null;

string username;
string userpsw;
string userlevel;



//编辑现有用户
private void BT_edit_Click(object sender, EventArgs e)
{

sda1.Update(ds, "a");
Databind();
}


//删除所选用户
private void BT_delete_Click(object sender, EventArgs e)
{

}

//重载控件
private void BT_refresh_Click(object sender, EventArgs e)
{
// 刷新datagridview 把当前的form重新加载
User_Load(sender, e);

}



//数据绑定方法




public void Databind()
{
SqlConnection scon1 = new SqlConnection("Data Source=acer-PC;Initial Catalog=cmis;Integrated Security=True;Pooling=False");
string sqlconnet1 = "select [username] '名称',[userpsw] '密码',[userlevel] '等级' from [users]";
SqlCommand scmd1 = new SqlCommand(sqlconnet1, scon1);
sda1 = new SqlDataAdapter(scmd1);
sda1.SelectCommand = scmd1;
SqlCommandBuilder scb = new SqlCommandBuilder(sda1);

sda1.InsertCommand = scb.GetInsertCommand();
sda1.DeleteCommand = scb.GetDeleteCommand();
sda1.UpdateCommand = scb.GetUpdateCommand();

try
{
scon1.Open();
ds.Clear();
sda1.Fill(ds, "a");
this.DATA_user.DataSource = ds.Tables[0];

}
catch (Exception ex)
{
MessageBox.Show("数据库异常");
}
finally
{
scon1.Close();
scon1.Dispose();
scmd1.Dispose();
sda1.Dispose();

}
}

private void User_Load(object sender, EventArgs e)
{
Databind();
}

[解决办法]

C# code

SqlCommand scmd1 = new SqlCommand(sqlconnet1);//下面行添加 ,scon1  sda1 = new SqlDataAdapter(scmd1,scon1);  sda1.SelectCommand = scmd1;  SqlCommandBuilder scb = new SqlCommandBuilder(sda1);
[解决办法]
ConnectionString配置不正确。