Initially Unselected DropDownList
- by Ricardo Peres
One of the most (IMHO) things with DropDownList is its inability to show an unselected value at load time, which is something that HTML does permit. I decided to change the DropDownList to add this behavior. All was needed was some JavaScript and reflection. See the result for yourself:
public class CustomDropDownList : DropDownList
{
public CustomDropDownList()
{
this.InitiallyUnselected = true;
}
[DefaultValue(true)]
public Boolean InitiallyUnselected
{
get;
set;
}
protected override void OnInit(EventArgs e)
{
this.Page.RegisterRequiresControlState(this);
this.Page.PreRenderComplete += this.OnPreRenderComplete;
base.OnInit(e);
}
protected virtual void OnPreRenderComplete(Object sender, EventArgs args)
{
FieldInfo cachedSelectedValue = typeof(ListControl).GetField("cachedSelectedValue", BindingFlags.NonPublic | BindingFlags.Instance);
if (String.IsNullOrEmpty(cachedSelectedValue.GetValue(this) as String) == true)
{
if (this.InitiallyUnselected == true)
{
if ((ScriptManager.GetCurrent(this.Page) != null) && (ScriptManager.GetCurrent(this.Page).IsInAsyncPostBack == true))
{
ScriptManager.RegisterStartupScript(this, this.GetType(), "unselect" + this.ClientID, "$get('" + this.ClientID + "').selectedIndex = -1;", true);
}
else
{
this.Page.ClientScript.RegisterStartupScript(this.GetType(), "unselect" + this.ClientID, "$get('" + this.ClientID + "').selectedIndex = -1;", true);
}
}
}
}
}
SyntaxHighlighter.config.clipboardSwf = 'http://alexgorbatchev.com/pub/sh/2.0.320/scripts/clipboard.swf';
SyntaxHighlighter.brushes.CSharp.aliases = ['c#', 'c-sharp', 'csharp'];
SyntaxHighlighter.all();
