How to conditionally change a control property in the presentation layer

Question

I'm not very experienced in ASP.Net, as I work mostly with PHP. I'm trying this, but it doesn't work:

<asp:TextBox runat="server" ID="txtAnswer" 
  TextMode='<%# IIf(DataBinder.Eval(Container.DataItem, "DoLargeInput"), "MultiLine", "SingleLine" )%>' Text=''></asp:TextBox>

DoLargeInput is a boolean.

Why doesn't this work?

I'm gettin the following error:

System.InvalidCastException: Conversion from string "MultiLine" to type 'Integer' is not valid. ---> System.FormatException: Input string was not in a correct format.
   at Microsoft.VisualBasic.CompilerServices.Conversions.ParseDouble(String Value, NumberFormatInfo NumberFormat)
   at Microsoft.VisualBasic.CompilerServices.Conversions.ToInteger(String Value)
   --- End of inner exception stack trace ---
   at Microsoft.VisualBasic.CompilerServices.Conversions.ToInteger(String Value)
   at Microsoft.VisualBasic.CompilerServices.Conversions.ToInteger(Object Value)
   at ASP.profile_questions_aspx.__DataBinding__control6(Object sender, EventArgs e)
   at System.Web.UI.Control.OnDataBinding(EventArgs e)
   at System.Web.UI.Control.DataBind(Boolean raiseOnDataBinding)
   at System.Web.UI.Control.DataBind()
   at System.Web.UI.Control.DataBindChildren()
   at System.Web.UI.Control.DataBind(Boolean raiseOnDataBinding)
   at System.Web.UI.Control.DataBind()
   at System.Web.UI.WebControls.Repeater.CreateItem(Int32 itemIndex, ListItemType itemType, Boolean dataBind, Object dataItem)
   at System.Web.UI.WebControls.Repeater.CreateControlHierarchy(Boolean useDataSource)
   at System.Web.UI.WebControls.Repeater.OnDataBinding(EventArgs e)
   at System.Web.UI.WebControls.Repeater.DataBind()
   at profile_questions.LoadObjects()

Any help would be greatly appreciated. Thanks!

Answer 1

Try:-

IIf(DataBinder.Eval(Container.DataItem, "DoLargeInput"), TextBoxMode.MultiLine, TextBoxMode.SingleLine

It the parse that will convert TextMode="MultiLine" approriately for you. At the point this binding code happens the parseing is over, you need to specify the value as you would in code.

Answer 2

The failed conversion to 'Integer' is because the TextMode property is a .NET enum, which is represented internally as an integer. TextBoxMode.MultiLine and TextBoxMode.SingleLine represent the correct kind of value.

On MSDN you can see the TextBox.TextMode property has type TextBoxMode.