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Complete Guide to Validation in Blazor: Client-Side and Server-Side Techniques

 In Blazor, you can perform validation using both client-side and server-side approaches. Client-side validation allows you to validate user input without making a round trip to the server, while server-side validation ensures that the data submitted by the client is valid on the server. Here's an overview of how you can perform validation in Blazor:

  1. Client-Side Validation:
    • Start by adding the System.ComponentModel.DataAnnotations namespace to your component file.
    • Define validation rules using attributes such as [Required], [Range], [RegularExpression], etc., on the properties of your model class.
    • In your Blazor component, bind the input fields to the corresponding properties of your model using the @bind directive.
    • To display validation error messages, use the ValidationMessage component and bind it to the property you want to validate.
    • You can also use the EditForm component to encapsulate your input fields and handle form submission.
    • When the user submits the form, the client-side validation will be triggered, and any validation errors will be displayed.

Here's an example of client-side validation in Blazor:

// MyModel.cs public class MyModel { [Required(ErrorMessage = "Name is required.")] public string Name { get; set; } [Range(18, 99, ErrorMessage = "Age must be between 18 and 99.")] public int Age { get; set; } } // MyComponent.razor <EditForm Model="@model" OnValidSubmit="HandleSubmit"> <div> <label>Name:</label> <InputText @bind-Value="model.Name" /> <ValidationMessage For="@(() => model.Name)" /> <label>Age:</label> <InputNumber @bind-Value="model.Age" /> <ValidationMessage For="@(() => model.Age)" /> </div> <button type="submit">Submit</button> </EditForm> @code { private MyModel model = new MyModel(); private void HandleSubmit() { // Perform form submission logic } }
  1. Server-Side Validation:
    • Define validation rules on the server-side by implementing the IValidatableObject interface in your model class.
    • Implement the Validate method and add your custom validation logic.
    • When the user submits the form, the server-side validation will be triggered, and any validation errors will be returned to the client.

Here's an example of server-side validation in Blazor:

// MyModel.cs public class MyModel : IValidatableObject { public string Name { get; set; } public int Age { get; set; } public IEnumerable<ValidationResult> Validate(ValidationContext validationContext) { var results = new List<ValidationResult>(); if (string.IsNullOrEmpty(Name)) results.Add(new ValidationResult("Name is required.", new[] { nameof(Name) })); if (Age < 18 || Age > 99) results.Add(new ValidationResult("Age must be between 18 and 99.", new[] { nameof(Age) })); return results; } } // MyComponent.razor <!-- Same as previous example --> @code { private MyModel model = new MyModel(); private void HandleSubmit() { var validationResults = model.Validate(new ValidationContext(model)); if (validationResults.Any()) { // Handle validation errors } else { // Perform form submission logic } } }

By combining client-side and server-side validation, you can ensure that user input is validated both on the client and the server, providing a robust validation mechanism in your Blazor applications.


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