Custom Controls 4

 You'll see later that you have to do something to make that happen and here all the set text box 1.txt equal to state drop-down list one.value thought you take so will take the value of the drop-down list and place it into the text box Save it all was run this page will selected value and it works correctly doesn't work faster than the user control that though once it's on the page ASP.net doesn't care with the code came from it still works the same way the real differences this control has a slightly better design time experience.

 Because it appears on the toolbox weakens drag it onto any page and what sincere we treat it like any other server control how does this control to his job let's look at the code before go to Florida here I want to look at properties and methods of this HTML text writer class we might be using is not look at the code yet was look at properties methods of writer the one that's useful is added attribute at attribute adds the specified markup and value to the opening Tagamet element that's useful we had already seen the right method there's the right attribute method.

 This one just writes the markup attribute value to the output stream were ever we are within the output is also you see the right begin tag right begin tag begins to write the output of the beginning of a tag) tag writes the complete and tag out there's right lie which rights out line obviously there's a default tab string the default tab string present a single tab character in case what is a tab into the output of your HTML and there also is the tag right care would outputs the closing angle bracket so should you want to use this writer to piece together the beginning portion of an element that some attributes in the closing right character you would use of this property to do the work so.

Now let's start back and look and see how this control doesn't strong the first thing it does is in the public constructor is called the base constructor and tells it what kind of element were creating this creates the output select tag around all the contents of this control is nice of the constructor accepts a parameter so you have to worry about creating the outermost element if step one was creating the control and calling the base class's constructor then step two involves adding control attributes this control requires some attributes it needs the base class attributes like style and position those things are generally provided by the base web control class we also need a unique ID which is required for data post back remember were try to keep track of the selected state we have survival post back sweetie unique ID to do that if auto post back is true we need an on change attribute which indicates client-side script to run.

Custom Controls 3

 That outputs Will reinvestigate our state drop-down list treating it as a custom control this time our user control version of the state drop-down list control was fine but what if you want a custom control what if you wanted to appear the toolbox like other controls what you want compiled into a separate assemblies was easy to deploy like other controls are sample includes a state drop-down list custom control in order to use this you to add the state drop-down list control the toolbox attitude to page set.

 Its auto post back property to true add code to do something with the selected value better rendered this control you have to remember that because it's a custom control it has to render all of its own HTML you need to end up with HTML that looks something like this that is we the select element a name property and ID property ASP.net requires the ID property then we need option elements for each option in the list and one of them is selected so we need the selected attribute for the one that is selected along with value and text information.

 For each item I like will we created the user control for the custom control we have to write code bit by bit output exactly this HTML to make this happen were going to use the HTML text writer class which you've already seen it in action the render and render contents methods of the base web control class are passed out HTML text writer object it's a stream into which you have to write the HTML output this class provides many methods and properties for creating HTML content it also contains several enumerations containing constants as well your party see that because we use the constants for creating a span element I've loaded the state list solution which includes our state drop-down list web control.

 You can see here we are class that inherits from the web control class before we investigate this code I'd like to try it out to do that I'll add to my solution a new website cultures ASP.net websites in the filesystem the name doesn't really matter to me saw click okay let's build this thing there we go and show this in design view and now in the toolbox there's a state drop-down list Dragon instance of it onto the page there is the state drop-down list that me set this is the start of project tries to run this where person five we make sure the auto post back property on this control is set to true there we go is for the text box on here as well there we go and now I'd like to react to an event of this control saw go to the events list and choose the selected index changed event actually I can make it easier I just double-click on the control and this goes automatically to the selected index changed event of this control and that requires some effort.

Custom Controls 2

 And quick to render HTML content at this point were just slamming out the text of this control will lets you use this control on the page go to add it to my solution a website that's fine that's fine that's fine limit rebuild everything by rebuilding everything I allow Visual Studio to play a fun trip and that is here in design view in the toolbox window once I've built my solution Visual Studio season has this server control available for use on this page it looks like a server control.

So they supply it as an option on the toolbox window I could drag this onto the page and because right now my server control has no text property it displays its ID property in square brackets the class they the server control one as the first instance of that control so as a server control one number one and if I come your change the text to the obligatory hello world the control updates to display that text will lets you run this page and see what's really going output when ASP.net renders the page with ASP.net renders this page we see in the browser for look at the source here a span tag.

 Which contains our control and here's hello world actually the span tag is how ASP.net represents a label is treating this like a label control well that's good enough we see that they've managed to spit out the HTML is required for this control what if I want to say a few have some I can come to my control and here in the override for the render contents method I just need to spit out some more HTML so I need to come out here and add a call to output.adding some way to write out the beginning of the span tag is a right for all begin tag methods courses also a right begin tag method which rights the opening tag with room to put attributes so the right begin tag won't put the closing bracket write full begin tag closes the opening tag of our span element.

 So I need here to figure how I put the span out this needs to be a strain I could just type the word span about 12 I will use HTML text writer tag is I love this because they give us enumeration which is all of the possible HTML elements I want span.2 strings there we go that's the begin tag at the end money the output. Right and tag HTML text writer tag.span.to string there we go save this go back to our page this rebuild everything I was view the page the browser and see what happens it looks the same if we look at the source you see that what we spit out now is a little more complicated the contents of our external span contains an internal span with the text property of our custom control in there so we've created a custom control and modify the HTML.