executereader无可用的连接,已关闭
if (this.comboBox1.SelectedItem.ToString () == "蜀山区 ")
{

if (dbcon == null)
{
dbcon = leiku.connection.sqlconnect();

}
SqlCommand sqlcmd0 = dbcon.CreateCommand();
sqlcmd0.CommandText = leiku.connection.getshushandiqu();
SqlDataReader sqlD = sqlcmd0.ExecuteReader();
if (sqlD.Read())
{
this.listBox1.Items.Clear();
this.listBox1.Items.Add(sqlD.GetString(0).Trim());

}
//sqlcmd.Dispose();
//sqlD.Close();
}
else if (this.comboBox1.SelectedItem.ToString () == "包河区 ")
{
SqlCommand sqlcmd1 = dbcon.CreateCommand();
sqlcmd1.CommandText = leiku.connection.getbaohediqu();
MessageBox.Show(sqlcmd1.CommandText.ToString());
SqlDataReader sqlB = sqlcmd1.ExecuteReader();
if (sqlB.Read())

{
this.listBox1.Items.Clear();
this.listBox1.Items.Add(sqlB.GetString(0).Trim());

}
//sqlcmd.Dispose();
//sqlB.Close();
}
为什么不加else if就行了.是不是前面的executereader没有释放啊.

[解决办法]
你加了Else if 后,dbcon就没有被初始化或连接,代码明显有问题