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ASP.NET Custom Controls. Custom Controls. Encapsulate Rich Functionality Reusable Redistributable. Types of Custom Controls. User Controls Server Controls. User Controls. Easy to create Easy to use Lack support for design-time features Scoped to a single application
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Custom Controls • Encapsulate Rich Functionality • Reusable • Redistributable
Types of Custom Controls • User Controls • Server Controls
User Controls • Easy to create • Easy to use • Lack support for design-time features • Scoped to a single application • Very similar to creating an ASPX page
Server Control • Harder to author • Done through code and not visually • Highly customizable design-time experience • Distributable to many applications
Creating Server Controls • Server Controls are derived from • System.Web.UI.Control • System.Web.UI.WebControls.WebControl • From any other control
System.Web.UI.Control • Base class for all controls • Doesn’t implement a user interface • Use this when you are creating nonvisual controls
System.Web.UI.WebControls.WebControl • Derives from System.Web.UI.Control • Adds User Interface features for handling • Most controls will derive from WebControl
All other controls • Used to set UI standards for a development group
Design-Time Attributes • Properties • Get/Set methods • Initialize the control • Attributes • Display information about properties • Categorize properties
UniqueID • Unique identifier of a control • Must be assigned to a control for the run-time methods to work
Run-Time Methods • CreateChildControls • Signals a composite control to create child controls • Dispose • Enables a controls to perform cleanup • LoadViewState • Customized state information restoration • SaveViewState • Customized state information persistence • Render • Send content to a browser
Render • Ultimate goal of a control is to display HTML in a browser • ASP.NET runtime will traverse all the controls in an ASPX page and call the render method on each one • Place the HTML that will be send in to the browser in the Render method
Generate HTML in Render • Generate raw HTML using the Write method of the HtmlTextWriter • Use the HtmlTextWriter helper functions • RenderBeginTag • RenderEndTag • AddAttribute (prior to RenderBeginTag) • AddStyleAttribute (prior to RenderBeginTag) • Client JavaScript can be rendered in the same way
Respond To Client Post • Must Implement System.Web.UI.IPostBackDataHandler • LoadPostData • Updates the state of the control as a result of a postback • Returns true if the state has changed, otherwise false • RaisePostDataChangedEvent • Will be called if LoadPostData returned true
Capture Postback Events • Implement IPostbackEventHandler • RaisePostBackEvent • Will be called when a postback event is caused • e.g. When a button is clicked • By default only the button and image button cause a postback • Can add a postback method to a control by using some simple client side JavaScript, the Render method and the GetPostBackEventReference method • Generating Client-Side Script for Postback (MSDN)
Maintaining State • Each server control has a ViewState property • Allows it to participate in state management • Can be used instead of a private field
Review • User Controls • Server Controls