![]() ![]() The second argument to SetError is the message to display. That allows the single ErrorProvider to simultaneously handle error messages for a multiplicity of controls. Note that the SetError method in the example takes a Control as its first argument. So the event occurs when you use the tab key to move away from the current control or when you click another control with the mouse. The Validating event occurs when a control yields focus to another control. You should be aware of several important facts that are not terribly clear from the documentation. You’d attach this method to the Validating event of a particular TextBox control called textBox1, either with the visual designer or programmatically with this code: += new CancelEventHandler(this.textBox1_Validating) When the input passes this validation test, the ErrorProvider.SetError invocation clears the existing error message, if any otherwise the catch block calls the ErrorProvider.SetError method to display the “Not an integer value” message. VISUAL STUDIO USING ERRORPROVIDER CODETo test the entered value, the code uses the Int32.Parse method, which throws an exception when the TextBox’s string value can not be converted to an integer. This code validates input into a TextBox, requiring that it be an integer. VISUAL STUDIO USING ERRORPROVIDER WINDOWSFor example, here’s a typical example that uses an ErrorProvider (from the MSDN article “ How to: Display Error Icons for Form Validation with the Windows Forms ErrorProvider Component“): protected void textBox1_Validating(object sender, CancelEventArgs e) Dragging an ErrorProvider onto the visual designer (or instantiating it in code) gives you the basic component required to display validation messages. ![]() To begin, you need to be aware of the handy Microsoft component called ErrorProvider (see the MSDN article “ ErrorProvider Component Overview“). Initial Solution: The ErrorProvider Component So, for example, you’ll find that the engine doesn’t handle validation interaction between multiple fields instead, I opted to focus on single-field validation for this introductory article. the effort expended to get this far would be multiplied five-fold). ![]() Also following the 80/20 rule, to cover the remaining use cases would require 80 percent of the effort (i.e. Instead, it follows the 80/20 rule: The validation engine will be useful in about 80 percent of the use cases you might need to address. This article presents a useful solution, though not a complete solution for every case. And you want to do this simply and easily. You want your program to validate form input, provide feedback to the user, and perhaps take other actions to handle the condition. You’ll find that using the validation engine discussed here, you can instrument a wide range of validation criteria with very few lines of code. The flexibility of storing validation settings in a configuration file makes validation easy to change, allowing developers and administrators to modifiy or customize validation properties without recompiling and redeploying?and without needing the source code. Visual Studio lets you specify property values at design time for a variety of components using that approach for defining validation attributes is a natural extension, and makes incorporating robust validation simpler for developers. A modular, data-driven validation engine approach provides a more natural interface, more flexibility, and is easier to maintain. The concept of considering the data qualities rather than the validation process leads to the validation engine discussed in this article. For example, if you were describing the input, you might say, “It should be between five and eight characters it should be numeric and non-negative it should always end in the digit ‘5,’ etc.” if this then that…) it’s far more intuitive to consider the qualities of the data to be validated. If you ever search MSDN for the topic, you’ll find most of the articles discuss hard-coded validation?but maintaining hand-written, custom code for each element that requires validation is a maintenance nightmare.įurthermore, it’s unnatural to conceptualize the steps of validation as programming steps (i.e. NET 2.0 provides some support for streamlining input validation, it barely scratches the surface of automating and simplifying the input validation process. Most developers craft hard-coded program logic to verify that a phone number consists of 7 or 10 digits that an IP address consists of 4 octets that a country name matches 1 of 193 choices, etc. Nput validation is something that every program needs, and every programmer dreads. ![]()
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