2006 - Basta!: Advanced server controls
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Daniel Fisher presented information on creating custom ASP.NET server controls. He discussed the lifecycle of controls, using properties, viewstate, events, databinding, hierarchical and inheritance aspects. He demonstrated several custom controls covering resources, events, AJAX, databinding, navigation and exceptions. Server control development allows encapsulating reusable logic but introduces overhead from viewstate and postbacks.
![17
ViewState in code
[Bindable(false),Category(“Appearance”),
DefaultValue(“This is the default text.”),
Description(“The text of the custom
control.”)]
public virtual string Text
{
get
{
object o = ViewState[“Text”];
if(o != null)
return (string) o;
else
return “This is the default text.”;
}
set { ViewState[“Text”] = value; }
}](https://image.slidesharecdn.com/advancedservercontrols-150617132441-lva1-app6892/85/2006-Basta-Advanced-server-controls-17-320.jpg)
![21
Events in code
• Custom event eventargs and handler
• The On[Event] Method
• Raising an Event
public class MyEventArgs : EventArgs {
public MyEventArgs(string prop1, string prop2) { ... }
}
public delegate void MyEventHandler(object sender, MyEventArgs e);
public event MyEventHandler ItemChanged;
protected virtual void OnItemChanged(MyEventArgs e) {
if(Events != null) {
MyEventHandler eh = (MyEventHandler) Events[MyItemChangedEvent];
if(eh != null)
eh(this, e);
}
}
OnItemChanged(new MyEventArgs(“prop1”, “prop2”));](https://image.slidesharecdn.com/advancedservercontrols-150617132441-lva1-app6892/85/2006-Basta-Advanced-server-controls-21-320.jpg)
![27
AJAX in code
var request = new Request();
function _getXmlHttp(){
/*@cc_on @*/
/*@if (@_jscript_version >= 5)
var progids =["Msxml2.XMLHTTP“,"Microsoft.XMLHTTP"];
for (i in progids){
try{
return new ActiveXObject(progids[i])
}
catch (e){}
}@end @*/
try{
return new XMLHttpRequest();
}catch (e2){ return null; }
}](https://image.slidesharecdn.com/advancedservercontrols-150617132441-lva1-app6892/85/2006-Basta-Advanced-server-controls-27-320.jpg)
![36
Hirarchical Controls in code
public class SlideNavMenu : Control
{
private List<SlideNavMenuItem> m_MenuItems = new List<SlideNavMenuItem>();
protected override void OnPreRender(EventArgs e)
{
for (int i = 0; i < this.Controls.Count; i++)
{
if (this.Controls[i] is SlideNavMenuItem)
{
this.m_MenuItems.Add((SlideNavMenuItem)this.Controls[i]);
}
else if (this.Controls[i] is LiteralControl || this.Controls[i] is Literal)
{
// nice try or whitespaces...
}
else
{
throw new ApplicationException("Wrong inner controls.");
}
}
}](https://image.slidesharecdn.com/advancedservercontrols-150617132441-lva1-app6892/85/2006-Basta-Advanced-server-controls-36-320.jpg)
2006 - Basta!: Advanced server controls
- 1. ASP.NET 2.0 Advanced Server Controls Daniel Fisher(lennybacon) newtelligence® AG
- 2. 2 About me • Software Engineer, newtelligence AG • Developer • Consultant • Trainer • Author for Developer Magazines • Expert & Editor for CodeZone.de • IIS, ADO.NET … • Leader of INETA UG VfL-NiederRhein • CLIP Member
- 3. 3 The Top 10 for better Webs • 1. Creating an n-Tier Design • 2. Working with Application Settings • 3. Creating Maintainable User Interfaces • 4. Creating Common Page Code • 5. Tracking Users' Actions • 6. Notifications of Exceptions • 7. Using State Properly • 8. Handling Unexpected Errors Gracefully • 9. Assigning Roles and Securing Web Pages • 10. There was no #10 ;-)
- 4. 4 Maintainable User Interfaces • It’s about reusability • Html mark-up • Server side code • Client side scripts
- 5. 5 ASP.NET Server Controls • Compiled code that can be reused in any ASP.NET web application. • Classes contained in the namespace System.Web.UI.WebControls are Server Controls, developed by Microsoft. • System.Web.UI.WebControls.Textbox • (and many, many more) • Use inheritance - all server controls come from System.Web.UI.WebControls.Control
- 6. 6 Server Controls Usage • Register Assembly, NS and TagPrefix • Use the Control <%@ Register Assembly=“MyAssembly” Namespace=“MyNamespace” TagPrefix=“MyPrefix” %> <MyPrefix:MyControl runat=“server” id=“MyControl1” />
- 7. 7 Server Controls Pro‘s • Encapsulate logic in reusable abstractions. • Clean mechanism to divide work across a team • Market growth of 3rd party products • Allows ISPs to provide even more value to for use in personal websites.
- 8. 8 Server Controls Con‘s • No visual way of developing server controls, generated via code.
- 9. 9 Something new … • Java Server Faces lent concepts from ASP.NET ;-) Quelle: Birgit Hauer
- 10. 10 Why Create Controls on your own • Once did something twice? • You need the functionality of two or more controls working in tandem, without having to write the logic in the web application. • Existing server control almost meets your needs, but only almost • None of the existing server controls meet your needs.
- 11. 11 Lifecycle of a control Instantiate : Constructor Initialize : OnInit method and Init Event Begin Tracking View State : TrackViewState Load View State : LoadViewState method Load Postback Data : IPostBackDataHandler.LoadPostdata method Load: OnLoad method and Load event Raise Changed Events : IPostBackDataHandler.RaisePostDataChangedEvent method Raise Postback Event : IPostBackEventHandler.RaisePostBackEvent method PreRender : OnPreRender method and PreRender event Save View State : SaveViewState method Render : Render method Unload : OnUnload method and Unload event Dispose : Dispose Method
- 12. 12 Processing • Control creation within the method CreateChildControls() • All display logic (aside from the necessary items in above step) should be done in the method OnPreRender(). • Rendering • Custom: Override Render() method and provide custom rendering logic • Composite: Combining multiple controls into one server control – Nothing to do?
- 13. 13 Resources • Strings • Javascript • Images • HttpHandlers - later
- 15. 15 Properties • Set variables to influence its rendering. • Almost all properties should be stored within View State?
- 16. 16 ViewState • ViewState is used to track and restore the state values of controls that would otherwise be lost • Base64 encoded - not easily readable, but not encrypted! • What to store • Integers • Strings • Floats • Decimals • Arrays of the data types stated above
- 17. 17 ViewState in code [Bindable(false),Category(“Appearance”), DefaultValue(“This is the default text.”), Description(“The text of the custom control.”)] public virtual string Text { get { object o = ViewState[“Text”]; if(o != null) return (string) o; else return “This is the default text.”; } set { ViewState[“Text”] = value; } }
- 18. 18 ViewState Concepts Send Request Send Response Send Request Send Response Ping Pong on the wire?
- 19. 19 ViewState alternatives • Query Request.Form and Request.QueryString on your own • Use local fields – most times they work fine
- 20. 20 Server Controls - Events • Event Handling is the best way of letting users tap into the processes of your control. • Providing events like Click for when a button is clicked, or SelectedIndexChanged when a new item has been selected in a drop down list enables developers to program in a very object oriented manner.
- 21. 21 Events in code • Custom event eventargs and handler • The On[Event] Method • Raising an Event public class MyEventArgs : EventArgs { public MyEventArgs(string prop1, string prop2) { ... } } public delegate void MyEventHandler(object sender, MyEventArgs e); public event MyEventHandler ItemChanged; protected virtual void OnItemChanged(MyEventArgs e) { if(Events != null) { MyEventHandler eh = (MyEventHandler) Events[MyItemChangedEvent]; if(eh != null) eh(this, e); } } OnItemChanged(new MyEventArgs(“prop1”, “prop2”));
- 22. 22 Demo • Events and delegates • EventControl
- 23. 23 The downside - Postbacks • Implement the IPostBackEventHandler • Create an event field • Create methods to relate to the event
- 24. 24 Postbacks - Alternatives • Server side only events • AJAX • Response.Redirect( http://example.org); • <a href=“…“>link</a>
- 25. 25 Demo • Server side only events • WaitScreen
- 27. 27 AJAX in code var request = new Request(); function _getXmlHttp(){ /*@cc_on @*/ /*@if (@_jscript_version >= 5) var progids =["Msxml2.XMLHTTP“,"Microsoft.XMLHTTP"]; for (i in progids){ try{ return new ActiveXObject(progids[i]) } catch (e){} }@end @*/ try{ return new XMLHttpRequest(); }catch (e2){ return null; } }
- 28. 28 Demo • AJAX, Response.Redirect() • UserManagement
- 29. 29
- 30. 30 Demo • <a href=“…“>link</a> • Forum
- 31. 31 Databound Controls • ObjectDataSource • SqlDataSource • … • Abstract way to access data • A lot of overhead but a standard way… • Who is your target?
- 32. 32 Databound in code private ITemplate _itemTemplate; public ITemplate ItemTemplate{ get{return _itemTemplate;} set{_ itemTemplate=value;} } protected override void CreateChildControls(){ CreateControlHierarchy(true); } protected virtual void CreateControlHierarchy(bool dBind){ LoadFromDataSource(); foreach (object r in _dataSource){ RepeaterItem item1 = CreateItem(ListItemType.Item, dataBind, r); } } private RepeaterItem CreateItem(…) { _itemTemplate.InstantiateIn(item); Controls.Add(item); }
- 33. 33 Demo • Databound Controls • DataBoundControl
- 34. 34 Hirarchical Controls • Navigations, Tabs … • ITemplate • ChildControls
- 35. 35 Hirarchical Controls - ChildControls • Limited liberty to the user • More control • More possibilities
- 36. 36 Hirarchical Controls in code public class SlideNavMenu : Control { private List<SlideNavMenuItem> m_MenuItems = new List<SlideNavMenuItem>(); protected override void OnPreRender(EventArgs e) { for (int i = 0; i < this.Controls.Count; i++) { if (this.Controls[i] is SlideNavMenuItem) { this.m_MenuItems.Add((SlideNavMenuItem)this.Controls[i]); } else if (this.Controls[i] is LiteralControl || this.Controls[i] is Literal) { // nice try or whitespaces... } else { throw new ApplicationException("Wrong inner controls."); } } }
- 37. 37 Demo • Hirachical controls • SlideNav
- 38. 38 HttpHandler • HttpHandlers have nothing to do with controls! • But you can use them to realize controls that • call dialogs • Do not need images or other resources in some directory…
- 39. 39 HttpHandler in code public class MembershipManagementAjaxHandler : IHttpHandler { public bool IsReusable{get{return true;}} public void ProcessRequest(HttpContext context) { Assembly asm = Assembly.GetExecutingAssembly(); Stream stream = asm.GetManifestResourceStream(_parameter); Image img = Image.FromStream(stream); img.Save(context.Response.OutputStream, System.Drawing.Imaging.ImageFormat.Gif); context.Response.End(); } }
- 41. 41 What ever you can imagine • …
- 43. 43 Inheritance • Whoever wants to extend your control, should be freely able to do so. • No matter who your target audience is or what functionality and features that your control provides, you will always find that one developer who will want to extend it for his/her own extra mile.
- 44. 44 Wrap-up • Server Control development is easy • The possibilities are endless • Creating a fully functional server control can take no longer than 15 minutes • You don’t need any “cool” application, Notepad can be your friend too – but intellisense is nice