结果与预期相反，因为if条件错误。

只需在条件中添加而不是，它应该按预期工作。

The result is opposite than the expected because the if condition is wrong.
Just add a not to the condition and it should work as expected.

if (!String.IsNullOrEmpty(myDataRowView["Signout_Time"].ToString()))
{
  //rest of code

如果不是，请告诉我。有帮助：）

Please let me know, if it doesn't helps :)

我发现了另一种更简单的方法emTemplae。这就是我做的事情

I have discovered another easier way of doing it in my ItemTemplae. this is what i did

<pre lang="ASP.NET"><asp:Button Visible='<%# string.IsNullOrEmpty(Eval("Signout_Time").ToString()) %>' runat="server" Text="Sign out" ID="out"  CommandName="SignOut" CommandArgument='<%#Eval("SN") %>'/>

这也是神奇的。两种解决方案都很完美

This also did the magic. Both solutions are perfect