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ASP.NET Controls

ASP.NET Controls. Lecture Overview. Identify the types of controls supported by ASP.NET and the differences between them. Categorizing Controls. There are two types of controls used in ASP.NET HTML controls are standard HTML controls understood by the browsers

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ASP.NET Controls

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  1. ASP.NET Controls

  2. Lecture Overview • Identify the types of controls supported by ASP.NET and the differences between them

  3. Categorizing Controls • There are two types of controls used in ASP.NET • HTML controls are standard HTML controls understood by the browsers • ASP.NET (Web) controls are processed by the server (IIS) and mapped to a complex array of HTML controls

  4. HTML Controls • Always map directly to HTML tags • All attributes are strictly compatible with HTML • They allow you to perform ‘some’ server side processing

  5. Web Server Controls • Are implemented by the ASP server as .NET Framework classes having a common .NET programming interface • It works very similar to the desktop applications • Web Server controls often have a richer programming interface

  6. Categorizing Server Controls ASP.NET CONTROLS WEB CONTROLS HTML CONTROLS

  7. The runat Attribute • The runat attribute makes a server control a server control • This is true for both HTML and Web controls • All tags without the runat attribute are copied verbatim to the output stream (HTTP response) • <asp:TextBox ID="TextBox3" runat="server"></asp:TextBox>

  8. Generalities • HTML controls and Web controls can sometimes to do the same thing • HTML controls can be used to conditionally create client-side script • Web controls generally provide a ‘richer’ programmatic interface • We often use a mix of both

  9. ASP.NET Server Controls (1) • These are unique to ASP.NET • All are contained in the System.Web.UI.WebControls namespace • All derive from WebControl • runat=“server” attribute is required or the markup will be rendered verbatim • The programming interface is intuitive and feels like attaching event handlers to desktop controls

  10. ASP.NET Server Controls (2) • Controls are object having methods, properties and events • Buttons are clicked • SelectedIndexChanged fires for list boxes and combo boxes • The wiring is a bit different

  11. ASP.NET Server Controls(Event Wiring 1) • ASP.NET Server controls have support events similar to their desktop countertops Names Match

  12. ASP.NET Server Controls (Properties 1) • ID – Name that will be used to reference the control instance programmatically (It’s the Name property that you are used to in VB) • Page – Page object on which the control resides • Parent – parent control instance • Use for container controls • Visible – Make the control instance visible or invisible • EnableViewState defines whether contents are persisted through view state

  13. ASP.Net Server Controls (Properties 2) • The Style property contains references to a collection of CSS style MyControl.Style[“border-color”] = blue; • The CssClass property contains the name of a defined CSS class • txtStyleDemo1.CssClass = "TextBox"

  14. ASP.NET Server Controls(Methods) • Focus – sets input focus to the control instance when it is rendered • HasControls – denotes whether this control instance has child controls • Controls – a collection of child controls • DataBind – binds the control instance to a data source

  15. ASP.NET Server Controls (Events) • Same page and control events discussed in the previous chapter • Init – First step in the life cycle • Load – occurs when the control is loaded into the page • PreRender – fires just before the page is rendered • Unload – control has been rendered. Use only to close files or release connections

  16. Help Pages (Note)

  17. HTML Controls (Overview) • HTML controls are similar to ordinary HTML controls • However, with the runat=“server” attribute added • ASP.NET adds a programmatic way to interact with the control instances on the server • ASP.NET controls are part of the System.Web.UI.HtmlControls namespace

  18. HTML Controls (Interface) • All HTML controls inherit from the HtmlControl class • The properties are simple • Attributes returns a collection of attribute / key value pairs • Style gets a CSS collection of applied CSS properties • Disabled indicates whether the control is disabled

  19. HTML Controls (Categories) • HtmlInputControl – These represent the variations of the <input> tag • HtmlContainerControl – These are Tables and other controls that contain other controls • See table 4-4 on page 113-114 • Other – Other controls such as <img> <a>

  20. HTML Control (Example) • Mark a <div> tag as a servers-side control • Store the date as the control’s inner HTML

  21. Using Server Controlswith JavaScript • So far, we have seen both client and server controls • But how do we get client-side JavaScript into our ASP.NET pages and call that code from the client? • Include client-side script into script blocks • Create dynamically with RegisterClientScriptBlock and RegisterStartupScript • As you will see, some controls rely on JavaScript to operate (LinkButton) ASP generates the code

  22. RegisterClientScriptBlock • Code is placed at the top of the page • Thus, the code executes “before” the page has completely loaded • Good to register functions but bad for referencing controls

  23. RegisterStartupScript • Code is placed at the end of the page • Use when you want to reference other page controls • Remember that HTML pages rendered and the DOM is processed sequentially

  24. RegisterClientScriptInclude • Again, the code appears at the beginning of the page • Use to grab a bunch of JavaScript from a file

  25. HTML Controls <a> • The HTMLAnchorclass implements <a> tags • <a> tags designated runat=“server” and having an id will be seen by the server <a id="BusinessNews" runat="server"></a>

  26. HTML Controls <a> • The href property contains the link • Store the text in InnerHtml or InnerText BusinessNews.HRef= "http://bloomberg.com"; BusinessNews.Title = Business news channel"; BusinessNews.InnerHtml = "<b>BusinessNews</b>";

  27. HTML Input Controls • All input controls derive from HtmlInputControl • Name is the read-only property containing the control name • Type property mirrors the Type attribute • Value contains text appearing in the control instance

  28. The ServerChange event • It fires for most HTML controls to denote that the control’s contents have changed from one postback to the next • Use for check boxes, radio buttons, text boxes, etc.

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