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asp.net building controls : New control from scratch....
I am curious...how do you go about building a new control from scratch? Just
for example, suppose you want to rebuild an asp:textbox control just like the one provided in the framework, but are not allowed to use the textbox base class. Is this even possible? This would involve drawing the textbox, then defining an area where text can be entered into it and handle some basic events such as OnTextChanged, etc. This example is not practical, but if the need did arise I am curious as how this can be accomplished? I am given the impression the sky is the limit in control building and am very interested in understanding how the .NET team built many of the their own base control library.
Chris,
Building a new control is not a rocket science. Basically, all you have to do is create a new class, which inherits either from System.Web.UI.Control or System.Web.UI.WebControls.WebControl. Use the former if you are planning to manage rendering completely on your own or if your control doesn't have anything to render and use the latter if you would like to use built-in style facilities. Once you have created this class, you have two options to pursue: a) Composition -- here you override CreateChildControls method to compose your newly created control out of existing controls, such as textbox. b) Rendering -- here you override the Render method and use the HtmlTextWriter, supplied as method's argument to render the HTML for the control. For more information, use MSDN library: http://msdn.microsoft.com/library/default.asp?url=/library/en-us/cpguide/html/cpcondevelopingwebformscontrols.asp Remember, there is no "drawing" going on -- all ASP.NET controls are simply chunks of HTML code. Thus, in order to learn how to render the control, you need to have a good understanding of how (D)HTML/CSS thing works. Hope this helps. :DG< [quoted text, click to view] "Chris Fink" <ChrisFink@discussions.microsoft.com> wrote in message news:82093A45-ECAF-44A0-BA4D-CBF1F5428BBB@microsoft.com... >I am curious...how do you go about building a new control from scratch? >Just > for example, suppose you want to rebuild an asp:textbox control just like > the > one provided in the framework, but are not allowed to use the textbox base > class. Is this even possible? This would involve drawing the textbox, > then > defining an area where text can be entered into it and handle some basic > events such as OnTextChanged, etc. This example is not practical, but if > the > need did arise I am curious as how this can be accomplished? I am given > the > impression the sky is the limit in control building and am very interested > in > understanding how the .NET team built many of the their own base control > library. > >
Dimitri,
Thanks for the response. Let me elaborate a little bit on my objective so the question makes the challenge a bit clearer - I believe the answer to this is that it cannot be done. What I want to accomplish is extending on the <select><option> html tags to make it appear on a web page just like the visual studio.net intellisense drop down list. This includes an image/icon to the left of each item and a dropdown list with more than one row displayed at a time (example <select id="isense" name="optSelect" size="7">) This will allow the user to use the scroll bar on the right of the drop down list to browse through items. The challenge in this is creating this functionality. I do not know any way to accomplish this desired affect. True, I can write a flyout menu using Javascript but this will not produce the scrollbar effect on the right hand side. The main problem using a flyout menu is that the amount of items in the list could become quite lengthy, just as in the .net intellisense window. So I pose the question. If you can't create controls from scratch by drawing them and they are not part of the underlying html/dom framework....how do you accomplish this? I understand the power of building controls is limited to their lowest common demoninator(html/javascript/dom specifications)....if you can't do it using DHTML that it can't be done..... Building controls will never be rocket science when we don't have the ability to build a rocket.....from scratch.... [quoted text, click to view] "Dimitri Glazkov" wrote:
> Chris, > > Building a new control is not a rocket science. Basically, all you have to > do is create a new class, which inherits either from System.Web.UI.Control > or System.Web.UI.WebControls.WebControl. Use the former if you are planning > to manage rendering completely on your own or if your control doesn't have > anything to render and use the latter if you would like to use built-in > style facilities. > > Once you have created this class, you have two options to pursue: > > a) Composition -- here you override CreateChildControls method to compose > your newly created control out of existing controls, such as textbox. > > b) Rendering -- here you override the Render method and use the > HtmlTextWriter, supplied as method's argument to render the HTML for the > control. > > For more information, use MSDN library: > > http://msdn.microsoft.com/library/default.asp?url=/library/en-us/cpguide/html/cpcondevelopingwebformscontrols.asp > > Remember, there is no "drawing" going on -- all ASP.NET controls are simply > chunks of HTML code. Thus, in order to learn how to render the control, you > need to have a good understanding of how (D)HTML/CSS thing works. > > Hope this helps. > > :DG< > > > "Chris Fink" <ChrisFink@discussions.microsoft.com> wrote in message > news:82093A45-ECAF-44A0-BA4D-CBF1F5428BBB@microsoft.com... > >I am curious...how do you go about building a new control from scratch? > >Just > > for example, suppose you want to rebuild an asp:textbox control just like > > the > > one provided in the framework, but are not allowed to use the textbox base > > class. Is this even possible? This would involve drawing the textbox, > > then > > defining an area where text can be entered into it and handle some basic > > events such as OnTextChanged, etc. This example is not practical, but if > > the > > need did arise I am curious as how this can be accomplished? I am given > > the > > impression the sky is the limit in control building and am very interested > > in > > understanding how the .NET team built many of the their own base control > > library. > > > > > >
Chris,
You may not be able to get exactly the same functionality as VS.NET intellisense, but you could get pretty darn close. True, you can not extend the existing SELECT element. However, I wouldn't even if I could. The purpose of the SELECT element is to populate form data, not to provide navigation. In your case, I would definitely go with DHTML. Scrollbars are possible to implement by setting CSS property overflow to "auto" or "visible" and controlling the height of your drop-down menu panel. As far as the number of the items is concerned, you should be able to get away with a 100 or so without visible performance impact. If you have lots more than that, I would question application design rather than attempt to create an all-satisfying solution. Also, I would not think of this development as one of creating a new HTML element like SELECT and such. You already have all HTML elements needed to accomplish your task: UL, LI, and A. All you're doing is changing the rendering of these elements using ECMAScript (the proper name of JavaScript) and CSS. :DG< [quoted text, click to view] "Chris Fink" <ChrisFink@discussions.microsoft.com> wrote in message news:2991E5F3-6403-4856-8E99-83C018733B26@microsoft.com... > Dimitri, > > Thanks for the response. Let me elaborate a little bit on my objective so > the question makes the challenge a bit clearer - I believe the answer to > this > is that it cannot be done. > > What I want to accomplish is extending on the <select><option> html tags > to > make it appear on a web page just like the visual studio.net intellisense > drop down list. This includes an image/icon to the left of each item and > a > dropdown list with more than one row displayed at a time (example <select > id="isense" name="optSelect" size="7">) This will allow the user to use > the > scroll bar on the right of the drop down list to browse through items. > > The challenge in this is creating this functionality. I do not know any > way > to accomplish this desired affect. True, I can write a flyout menu using > Javascript but this will not produce the scrollbar effect on the right > hand > side. The main problem using a flyout menu is that the amount of items in > the list could become quite lengthy, just as in the .net intellisense > window. > > So I pose the question. If you can't create controls from scratch by > drawing them and they are not part of the underlying html/dom > framework....how do you accomplish this? I understand the power of > building > controls is limited to their lowest common demoninator(html/javascript/dom > specifications)....if you can't do it using DHTML that it can't be > done..... > > Building controls will never be rocket science when we don't have the > ability to build a rocket.....from scratch.... > > > "Dimitri Glazkov" wrote: > >> Chris, >> >> Building a new control is not a rocket science. Basically, all you have >> to >> do is create a new class, which inherits either from >> System.Web.UI.Control >> or System.Web.UI.WebControls.WebControl. Use the former if you are >> planning >> to manage rendering completely on your own or if your control doesn't >> have >> anything to render and use the latter if you would like to use built-in >> style facilities. >> >> Once you have created this class, you have two options to pursue: >> >> a) Composition -- here you override CreateChildControls method to compose >> your newly created control out of existing controls, such as textbox. >> >> b) Rendering -- here you override the Render method and use the >> HtmlTextWriter, supplied as method's argument to render the HTML for the >> control. >> >> For more information, use MSDN library: >> >> http://msdn.microsoft.com/library/default.asp?url=/library/en-us/cpguide/html/cpcondevelopingwebformscontrols.asp >> >> Remember, there is no "drawing" going on -- all ASP.NET controls are >> simply >> chunks of HTML code. Thus, in order to learn how to render the control, >> you >> need to have a good understanding of how (D)HTML/CSS thing works. >> >> Hope this helps. >> >> :DG< >> >> >> "Chris Fink" <ChrisFink@discussions.microsoft.com> wrote in message >> news:82093A45-ECAF-44A0-BA4D-CBF1F5428BBB@microsoft.com... >> >I am curious...how do you go about building a new control from scratch? >> >Just >> > for example, suppose you want to rebuild an asp:textbox control just >> > like >> > the >> > one provided in the framework, but are not allowed to use the textbox >> > base >> > class. Is this even possible? This would involve drawing the textbox, >> > then >> > defining an area where text can be entered into it and handle some >> > basic >> > events such as OnTextChanged, etc. This example is not practical, but >> > if >> > the >> > need did arise I am curious as how this can be accomplished? I am >> > given >> > the >> > impression the sky is the limit in control building and am very >> > interested >> > in >> > understanding how the .NET team built many of the their own base >> > control >> > library. >> > >> > >> >> >>
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