Custom Controls

Custom Controls

From Section 6.6.2 of the book

This is an example of a Custom Control that can be used to fold away text parts in web pages and to replace them with background text parts. The control is implemented as a class Fold, which is derived from the class ImageButton:

Fold.cs

using System;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.IO;

namespace Folds {

[ParseChildren(false)]
public class Fold : ImageButton {
  
  public event EventHandler FileNotFound;
  
  public string Text {
    get { return ViewState["Text"]==null ? "" : (string)ViewState["Text"]; }
    set { ViewState["Text"] = value; }
  }
  
  public string Icon {
    get { return ViewState["Icon"]==null ? "Solid" : (string)ViewState["Icon"]; }
    set { ViewState["Icon"] = value; }
  }
  
  public Fold() : base() {
    Click += new ImageClickEventHandler(FoldClick);
  }
  
  protected override void AddParsedSubObject(object obj) {
    if (obj is LiteralControl) AlternateText = ((LiteralControl)obj).Text;
  }
  
  void FoldClick(object sender, ImageClickEventArgs e) {
    string s = Text;
    Text = AlternateText;
    AlternateText = s;
    if (Icon == "Solid") Icon = "Hollow"; else Icon = "Solid";
  }
  
  protected virtual void OnFileNotFound(EventArgs e) {
    if (FileNotFound != null) FileNotFound(this, e);
  }
  
  protected override void OnClick(ImageClickEventArgs e) {
    try {
      if (AlternateText.StartsWith("@")) {
        string fileName = Page.MapPath(TemplateSourceDirectory) 
          + "/" + AlternateText.Substring(1);
        FileStream s = File.OpenRead(fileName);
        StreamReader r = new StreamReader(s);
        AlternateText = r.ReadToEnd();
      }
    } catch (FileNotFoundException) {
      OnFileNotFound(EventArgs.Empty);
    } finally {
      base.OnClick(e);
    }
  }
  
  protected override void Render(HtmlTextWriter w) {
    w.Write("<" + "input type=image name=" + this.UniqueID);
    w.Write(" src='" + TemplateSourceDirectory + "/" + Icon + "Left.gif' border=0 />");
    w.Write(Text);
    w.Write("<" + "img src='" + TemplateSourceDirectory + "/" + Icon + "Right.gif'>");
  }
}
}

This class must be compiled into a DLL which must be stored in a subdirectory /bin under the virtual directory. The compilation command looks like this:

  csc /target:library /out:bin/Folds.dll Fold.cs

Now the Custom Control can be used in an aspx page.

Fold.aspx

<%@ Page Language="C#" %>
<%@ Register TagPrefix="my" Namespace="Folds" Assembly="Folds" %>
<html>
  <body>
    <form Runat="server">
      <my:Fold Text="Please read!" Runat="server">
        ASP.NET allows the development of custom controls
        that open up almost unlimited possibilities for
        new web functionality.
      </my:Fold>
    </form>
  </body>
</html>

Try it

http://dotnet.jku.at/book/samples/6/Fold.aspx