Creating Desktop Applications in .NET Core 3

In my job, I still do a fair amount of work desktop related work which means when I heard that .NET Core 3 is going to bring support for Winforms and WPF I got pretty excited. This post is going to show you how to installing the preview of .NET Core 3 and then using the .NET CLI to a new Winforms or WPF application.

This information was covered in the .NET Core 3 Preview 1 announcement from December, but I thought I might as well document it here as I was trying it out.

Download and Install

Head over to the .NET Core 3 download  page and select the SDK for your OS. Keep in mind that Winforms and WPF will only run on Windows machines unlike the rest of .NET which is cross-platform. After the download is complete run the installer and follow the prompts.

Project Creation

Using the .NET CLI you can use the following command to create a Winform application.

dotnet new winforms

Of the following to create a WPF application.

dotnet new wpf

After the project is created for either type you can use the following command to run the application.

dotnet run

The following is an example of what you would see for a new WPF application.

Limitations

If you are going to be playing with the desktop-based framework I recommend that you grab the preview of Visual Studio 2019. Even with the preview, there are no designers available Winforms or WPF as of the time of this writing.

Wrapping Up

I know Microsoft has shown some neat demos, but in this first preview doesn’t have much tooling around it so if you are going to do much more than the new applications as I did above you are going to be in for a lot of manual work. Please don’t take this as a dig, as I said above I am very excited about this functionality.

If you are wondering about what versions of Windows .NET Core 3 will be supported on that information can be found here.

Data Annotations

Validation via data annotations in .NET is a great feature that is simple to implement. Here is an example model class that is using data annotations.

using System.ComponentModel.DataAnnotations;

namespace Contacts.Models
{
    public class Contact
    {
        [Required]
        [StringLength(50, MinimumLength = 4)]
        public string Name { get; set; }
        [StringLength(2)]
        public string State { get; set; }
        [Display(Name = "Zip Code")]
        [StringLength(10)]
        public string ZipCode { get; set; }
    }
}

First step in using data annotations is to add a using statement for the System.ComponentModel.DataAnnotations namespace. This namespace allows you to add validation attributes to the properties that require validation and contains helper classes to run validate on attributed models.

In the example above Required, StringLength and Display are all validation attributes. For the most part the attributes are self-explanatory, but be aware most attributes also have options to give you more control of the validation. For example required attribute has an AllowEmptyStrings property that if set to true will allow an empty string to pass validation. String length is another example which has options for minimum and maximum lengths for the property being validated.

This is just a small sample of the built-in attributes that exist. Other built-in attributes range  from credit card and email address validation to file extension and range validation. If a built-in validation does not meet your needs then a custom attribute a can be created by deriving from ValidationAttribue.

MVC has a lot of great functionality built around data annotations. For instance as long as a client has JavaScript turned a form will not allow submission until the model passes all the validation conditions. On the server-side inside of a controller to run validation all it takes is to run ModelState.IsValid.

With winforms the story is not quite as simple, but still pretty straight forward. The following is a simple example of calling validation on a model.

private void ValidationExample()
{
    var contact = new Contact { Name = "Bob", State = "TN" };

    var context = new ValidationContext(contact);
    var errors = new List<ValidationResult>();

    if (!Validator.TryValidateObject(contact, context, errors))
    {
        foreach (ValidationResult result in errors)
        {
            //act on error
        }
    }
}

Validator.TryValidateObject takes the model to be validated, a validation context (created with the model to validate) and an empty list of type ValidationResult. The function call returns false if any properties fail validation. In the example above the validation would fail since name only contains three characters the minimum length is set to four characters.