Developing and Using Custom User Controls in ASP.NET

Once you have created a user control and specified properties on that user control, you can change those property values both declaratively and programmatically from the page that contains the user control.

Declaratively setting property values for a custom control is quite simple. Unfortunately, programmatically accessing a user control from the Web Forms Page's code-behind involves a few extra steps.

Although Delphi normally adds a member variable corresponding to each control you place on the page so that you can program against the control, it does not do this for user controls. You need to modify the page unit file manually to be able to access its properties and methods.

Accessing a User Control Programmatically

1. Add the name of the unit file where the ContactInfo.ascx class is defined to the uses section of the Web Forms page declaration.
2. Add a declaration to the strict protected section of the TUserControlTest declaration.
3. Access the properties of the user control in any of the event handler or methods of the page where you placed an instance of the user control.

 TContactInfo = class(System.Web.UI.UserControl)
 ...
 private
    FEmail : string;
 public
    function GetEmail: string;
    procedure SetEmail(const Value: string) ;
 
    property Email : string read GetEmail write SetEmail;
 end;
 ...
 implementation
 ...
 procedure TContactInfo.SetEmail(const Value: string) ;
 begin
    emailLabel.Text := '<a href="mailto:' + Value + '">Mail me</a>';
 end;
 
 function TContactInfo.GetEmail: string;
 begin
    result := FEmail;
 end; 

Now, back to programmatically setting the Email property:

 unit UserControlTest;
 
 interface
 
 uses
    ContactInfo, ... ;
 
 type
    TUserControlTest = class(System.Web.UI.Page)
    ...
    strict protected
      UserControl1 : TContactInfo;
    ...
    end;
 
 implementation
 ...
 procedure TUserControlTest.Page_Load(sender: System.Object; e: System.EventArgs) ;
 begin
    UserControl1.Email := 'delphi.guide@about.com';
 end; 

By now, you know how to add user controls on a Web Forms page at design-time. In real world applications you'll want to be able to dynamically load a user control and place it on the page.

Dynamically Loading User Controls

The LoadControl method returns a type of the Control class, and you need to cast the user control to the appropriate strong type to be able to set individual properties on the control.

Here's how to dynamically create an instance of the ContactInfo user control and add it to a Panel object (named Panel1) :

 procedure TUserControlTest.Page_Load(sender: System.Object; e: System.EventArgs) ;
 var
    contactInfo : TContactInfo;
 begin
    contactInfo := Page.LoadControl('~/Controls/ContactInfo.ascx') as TContactInfo;
    contactInfo.Contact := 'Zarko Gajic';
    contactInfo.Email := 'delphi.guide@about.com';
 
    Panel1.Controls.Add(contactInfo) ;
 end;
 

To the next chapter: A Beginner's Guide to ASP.NET Programming for Delphi developers

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>> Handling Custom User Control Events, View State, Postbacks, ...

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