c# barcode maker Lesson 1: Performing input validation in C#

Paint Quick Response Code in C# Lesson 1: Performing input validation

Lesson 1: Performing input validation
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In this lesson, you will learn how the validation framework operates and how you can use the validation controls that are included in ASP.NET to perform input validation.
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ChAPTER 5
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Input Validation and Site Navigation
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After this lesson, you will be able to:
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Understand the validation framework. Add validation controls to a webpage. Configure validation controls. Implement the CustomValidator control. Test for valid user input.
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Estimated lesson time: 60 minutes
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Understanding the Validation Framework
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A common problem for developers is ensuring that data entered by users is valid. That problem is made more difficult when the application exists in a web browser. When the data is sent from the browser to the server, you need to make sure that the data is valid. In addition, users expect some feedback and assistance entering valid data before they spend the time sending it to the server for a response. Fortunately, ASP.NET has a built-in data validation framework for handling this scenario. It provides a straightforward way to accomplish both client-side and server-side validation with minimal coding. Client-side validation is a convenience to users, but it is not a security feature. It improves performance by checking the data at the browser before sending the data to the server. This avoids unnecessary communication with the server. Client-side validation isn t a security feature because a malicious user could easily bypass the client-side validation. Only server-side validation can improve security. Fortunately, ASP.NET makes it easy to build both client-side and server-side validation into webpages.
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Adding Validation Controls to Your Page
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Validation controls are found in the Visual Studio Toolbox. You add them to a webpage the same way you add other controls. The following are the basic steps for using a validation control on a webpage:
1. 2.
Open a webpage in Design view, and open the Visual Studio Toolbox. Add the input controls that require validation, such as TextBox and RadioButtonList controls. Navigate to the Validation tab of the Toolbox. Drag the desired validation control next to (or near) the control you intend to validate. For example, you might drag a RequiredFieldValidator control next to a TextBox control to ensure that a user enters data in the text box. Next, you set the ID property of the validation control (from Source view or in the Properties window). To enhance your code s readability, use a name for the control that is similar to the field it validates. For example, if you are validating a TextBox control named NameTextBox, you might name the validator NameTextBoxValidator.
Lesson 1: Performing Input Validation
ChAPTER 5
4. 5.
The next step is to set the validation control s ControlToValidate property to the control being validated. Set the ErrorMessage property to something that will be meaningful to the user. The value set as the ErrorMessage will be displayed to users as assistance when they try to submit the form with invalid data. This message is typically put into a ValidationSummary control on the page. Set the Text property of the validation control to display a message to the user at the validation control location if validation fails. If you plan to display validation error messages in a ValidationSummary control, set the Text property to a short string such as an asterisk (*). Keeping this short minimizes the space that is required by the validation control but still offers a visual cue to the user that something is wrong with the item. If you do not display the full error message in the Text property, set the validation control s tooltip property to be the same as or similar to the ErrorMessage property. This value will display when the user points to the validation control s text after validation fails. Set the Display property to None to prevent the display of the Text property if validation fails. If you want to display the Text property, set Display to Static to leave a blank space where the error message will appear prior to validation. Otherwise, set Display to Dynamic to reformat the ASP.NET output around the Text if validation fails. Optionally, add a ValidationSummary control to display all the validation error messages in one location after the user has triggered page-level validation by clicking a submit button. This is especially useful in scenarios in which the webpage is crowded with other controls, and displaying the validation error message next to the invalid control presents a difficult layout situation. Typically, you should place the ValidationSummary either near the submit button or at the top of the page. When the ShowMessageBox property is set to true, the ValidationSummary control will display a pop-up message with the validation errors in lieu of, or in addition to, displaying the validation errors on the webpage.
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