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In building the ASP. NET page framework, it was important to try and make the task of validating input a lot easer than it has been in the past. Each time you get a request, you need to write code to check the input and write any errors the user has made back to the page to help the user to correctly fill in the form. This is a taxing process for end users, developers, and servers alike.
DTHML and scripting languages improve things somewhat. It is possible to provide the user with immediate feedback on bad input and to prevent them from posting a page until it has been corrected. However, it can be almost impossible to guarantee that every user of your site has the required scripting environment.
This usually means that if you want to use script to improve the interface of your pages, you have to write the same validation logic twice, once on the client, and again on the server, just in case the client script cannot be executed.
We visited a large number of real pages to determine the sort of scenarios these components needed to be able to handle. We wanted to dramatically reduce the amount of validation code needed for future applications. The validator controls are the main elements of the solution.
A validator is a visual ASP. NET control that checks a specific validity condition of another control. It generally appears to the user as a piece of text that displays or hides depending on whether the control it is checking is in error. It can also be an image, or can even be invisible and still do useful work. There are five types of validator controls that perform different types of checks.
Another element in our solution is the ValidationSummary control. Large data entry pages generally have an area where all errors are listed.
The ValidationSummary automatically generates this content by gathering it up from validator controls on the page. The final element is the Page object itself.
It exposes the all-important "IsValid" property, which you check in server code to determine if all of the user input is OK. Most Web sites do all of their validation checks on the server. You need to write the server-based checks anyway for clients without script, so it can be hard to justify writing it all over again for rich clients. Validation controls change all that, because almost all the duplicated logic is encapsulated in the controls. If a client with Internet Explorer 4.
In order to use validators effectively, it helps to have a firm definition of what they are. Let's refine our previous definition a little:. This is an important definition, because it means that you frequently need to use more than one validator control for each input control. For example, if you want to check whether or not user input in a text box is a nonblank, b a valid date between a particular range and c less than the date in another text input control, you would want to use three validators.
While this might seem cumbersome, remember that to be helpful to the user, you would want to have three different text descriptions for all these cases. To demonstrate validation, we will walk through the process of adding validation to an existing page. Here are some example requirements:. In front of each field, we add a RequiredFieldValidator. The error message is reported in a summary. The final step is to add a validation summary to the top of the page like so:.
Next we need to enforce the character requirements for the User ID and Password fields. For these we will use RegularExpressionValidator controls. Regular expressions can be very powerful in concisely expressing checks for this sort of information, as well as ZIP codes, phone numbers, and e-mail addresses. Note that in this case we did not specify any inner content within the tag. The inner text is equivalent to the Text property of the control.
If it is blank, the error message will be displayed where the control is positioned, as well as appearing in the summary. The password checks can be done with the following two validators. If you use more than one, they must all match before the input is considered valid. We need to make sure the password re-entry field matches the password. We will use the CompareValidator to do this, since it is capable of working with two input controls at a time:.
By default, CompareValidator does a simple string match comparison. If required, it can do more complex comparisons involving dates and numbers. The final thing we need to check is that the name is not already taken in our hypothetical site.
We will check this during the validation process. Use a regular expression for validation: OK — we are moving right along here. Now we gotta tie it all together.
We will do that using the Validate method. During this process the method will check all its settings and determine if the control is valid or not, and then update the client accordingly.
You will need to call this method from your data submit button. This means that the validation is occurring at the server. More on this later.
To get this to work with the page and more importantly the validation summary you have to let the page know it has a control with validation capability. Do this by adding it to the Page's Validator's collection when the control Initializes. Basically the OnInit is part of the base class Text Box functionality, you are just extending it. So all that being done, I want to point out a major shortcoming with this control.
Looks like I will get out the reflector tool and decompile those validator controls. You now have your own control. The next article will be on how to put it into Visual Studio.
Welcome to Geeks with Blogs. Invalid syntax near' in ASP. Net New Geek in Town. Steal This Code All good programmers borrow at least part of their code. So feel free to borrow some of mine. Comments on this post: When you build the control this way you have to reproduce a lot of the functionality already built in to the existing controls by stubbing out and coding the interfaces.
You are basically creating a composite control. Is there a way to do this by creating a full custom control that's just a wrapper around a textbox control and a regular expression validator control?
Seems like it would be easy to do but I couldn't find any examples of it. Here's some pseudo code I tried to create a sample based on the above but I got errors about the Regular Expression control being set to 'null'. Odd since the constructor sets it to new. Anyway, any ideas you have would be appreciated. Left by Brian on Aug 29, I did consider this approach as well, mainly for the same reasons that you did, and one more reason. I was considering adding a label to the control, so it came prelabeled with the data entry prompt.
In the overall scheme of things, I didn't go down that path because I don't like the validators in dotNet. I plan on extending this control to add in many different validation capabilities.
Already the control can check to see if an entry is required as well as apply a regular expression. It reamains in my mind a lot more extensible and compact than if we added all the validators to a generic control as you describe above.
Does that logic hold water? Still, there is a place for composite controls. I come back to label control being part of a text box control. So I guess the next step is for me to try adding a label to the validator, and see how far I get. Left by JT on Aug 29, Left by Kevin Hansen on Dec 28, 4: Left by Prakash Koshti on Apr 18, 6: