無效試圖調用元數據時，讀取器已關閉

Question

我使用下面的代碼從表

SqlCommand cmd1 = new SqlCommand(); 
SqlDataReader reader1 = null;    
cmd1.CommandType = CommandType.Text; 
cmd1.Connection = conn; 
cmd1.CommandText = "......";    
reader1 = cmd1.ExecuteReader(); 

while (reader1.Read()) 
{ 
    Label32.Text = (reader["Unit"]).ToString(); 
} 

連接打開檢索列的任何想法。我的問題是，當從表中檢索到空值時，列中有很多空值。它會給我錯誤「無效嘗試在閱讀器關閉時調用MetaData。」我怎麼能解決這個問題。謝謝。

在「Label32.Text =（reader [」Unit「]）上引發了異常ToString（）;」

堆棧跟蹤：

at System.Data.SqlClient.SqlDataReader.get_MetaData() 
at System.Data.SqlClient.SqlDataReader.CheckMetaDataIsReady() 
at System.Data.SqlClient.SqlDataReader.GetOrdinal(String name) 
at System.Data.SqlClient.SqlDataReader.get_Item(String name) 
at TSOD._1Test.Page_Load(Object sender, EventArgs e) in h:\TSODNEW\TSOD\1Test.aspx.cs:line 75 
at System.Web.Util.CalliEventHandlerDelegateProxy.Callback(Object sender, EventArgs e) 
at System.Web.UI.Control.OnLoad(EventArgs e) 
at System.Web.UI.Control.LoadRecursive() 
at System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean      includeStagesAfterAsyncPoint) 

Answer 1

試試這個：

while (reader1.Read()) 
{ 
    Label32.Text = (reader1["Unit"]).ToString(); 
}