Required field validators in windows forms

Show "Please check one radio button! Show "Please select a value from comboBox! I wouldn't really recommend that, it's really annoying as a user to see that kind of validations. I would rather place labels to warn him about all his mistakes at once. That is a terrible, terrible form of validation. At very least, rather put all the errors in a list, and display that list after validation.

I can't imagine how I would hate using your software if I was new, made errors, and then had to close ten million message boxes. ProfK Upvoted Show "Please check the radio button" ; newRadioButtons[inti]. Show "Please fill the text box" ; newTextBox[inti]. I like this approach, I had a small form that needed some validation and went for this, simple to implement and maintain for small forms — Nelson. Try using Validating event of the control and code whatever validation you need in there.

Object, ByVal e As System. CancelEventArgs Handles Textbox. Validating If Not ValidateEmail sender. Text Then sender. ErrorBackgrounColor e. Re:Arek's comment as I can't comment there yet. I agree that comments that pop up when you can't leave or have to click may be annoying so it is better to colour stuff or make a list of errors which is displayed after user clicks a button or add a label show it as Arek's suggested. Update the namespaces in the last using statement for the Shared project and the namespace for the controller class.

In addition to data annotations validation client-side and server-side , the controller validates that a value is provided for the ship's description Description if the user selects the Defense ship classification Classification.

The validation for the Defense ship classification only occurs server-side in the controller because the upcoming form doesn't perform the same validation client-side when the form is submitted to the server. Server-side validation without client-side validation is common in apps that require private business logic validation of user input on the server.

For example, private information from data stored for a user might be required to validate user input. Private data obviously can't be sent to the client for client-side validation.

The StarshipValidation controller in this section uses Microsoft Identity 2. Access " scope for this API. For a version of the controller that works with Microsoft Identity 1.

NET Core prior to version 5. If using the preceding controller in a hosted Blazor WebAssembly app, update the namespace BlazorSample. Controllers to match the app's controllers namespace. When a model binding validation error occurs on the server, an ApiController ApiControllerAttribute normally returns a default bad request response with a ValidationProblemDetails. The response contains more data than just the validation errors, as shown in the following example when all of the fields of the Starfleet Starship Database form aren't submitted and the form fails validation:.

To demonstrate the preceding JSON response, you must either disable the form's client-side validation to permit empty field form submission or use a tool to send a request directly to the server API, such as Fiddler , Firefox Browser Developer , or Postman. If the server API returns the preceding default JSON response, it's possible for the client to parse the response in developer code to obtain the children of the errors node for forms validation error processing.

It's inconvenient to write developer code to parse the file. Ideally, the server API should only return the validation errors:. To modify the server API's response to make it only return the validation errors, change the delegate that's invoked on actions that are annotated with ApiControllerAttribute in Program. For any other API endpoints, preserve the default behavior by returning the object result with a new ValidationProblemDetails. Add the Microsoft. Mvc namespace to the top of the Program.

In Program. For more information, see Handle errors in ASP. In the Client project, add the CustomValidation component shown in the Validator components section. Update the namespace to match the app for example, namespace BlazorSample.

In the Client project, the Starfleet Starship Database form is updated to show server validation errors with help of the CustomValidation component.

The errors are available in the form's EditContext for display by the form's validation summary. In the following FormExample6 component, update the namespace of the Shared project using BlazorSample. Shared to the shared project's namespace. Note that the form requires authorization, so the user must be signed into the app to navigate to the form. As an alternative to the use of a validation component , data annotation validation attributes can be used.

The server-side validation approach in this section is suitable for any of the Blazor WebAssembly hosted solution examples in this documentation set:. Use the InputText component to create a custom component that uses the input event instead of the change event.

Use of the input event triggers field validation on each keystroke. The following CustomInputText component inherits the framework's InputText component and sets event binding to the oninput event. The example in this section is based on the Starfleet Starship Database form of the Example form section of this article.

Add the following enum types to the app. Create a new file to hold them or add them to the Starship. In the following example, properties are added to the Starship model described in the Example form section:.

Add the components to produce:. Nested radio button groups aren't often used in forms because they can result in a disorganized layout of form controls that may confuse users. However, there are cases when they make sense in UI design, such as in the following example that pairs recommendations for two user inputs, ship engine and ship color. One engine and one color are required by the form's validation. However, the user can combine any engine with any color to submit the form.

The ValidationSummary component summarizes all validation messages, which is similar to the Validation Summary Tag Helper :. Specify the field for validation with the For attribute and a lambda expression naming the model property:. The default validation-message class sets the text color of validation messages to red:.

To ensure that a validation result is correctly associated with a field when using a custom validation attribute , pass the validation context's MemberName when creating the ValidationResult. GetService is null. Injecting services for validation in the IsValid method isn't supported. In the following example, valid validField and invalid invalidField styles are specified.

Create a class derived from FieldCssClassProvider that checks for field validation messages and applies the appropriate valid or invalid style. The preceding example checks the validity of all form fields and applies a style to each field. If the form should only apply custom styles to a subset of the fields, make CustomFieldClassProvider apply styles conditionally.

For any fields with names not matching Name , string. Empty is returned, and no style is applied. However, field validation runs normally. If more than 10 characters are provided, the validation summary indicates the error:. Any other fields apply logic similar to Blazor's default logic and using Blazor's default field CSS validation styles, modified with valid or invalid.

ErrorProvider , ToolTip , and Validator - these components provide a mechanism which extends controls' or components' properties, in the property window. You will see text like "Type on validator1", which means Type property is an extended property and is provided by the validator1 control or component.

To have this amazing feature:. In Validator , I define an extended property for the control. Actually, a property window only provides a simple text input editor as default. How do Color and Lines properties do this? Using the Reflector v4.

Color struct in the System. Disassemble the System. The Editor attribute can be applied to either a class struct or a property. If class A applies the Editor attrubute, any other class can define properties of class A. Those properties will always be edited by the specified editor in the property window. Answered by:. Archived Forums. Web Forms. Sign in to vote. Then in my code I'm Inserting a new ListItem with value of The dropdownlist holds roles. If the person I choose has a role, and I go from their selected role back to the default, the validator works, but if the person has no role and --Select a Role-- is the value selected, the validator isn't working.