get-started-counter-csharp-mvvm.md

uid
Uno.Workshop.Counter.CSharp.MVVM

Counter App using C# Markup and MVVM

Download the complete C# Markup + MVVM sample

[!INCLUDE Intro]

In this tutorial you will learn how to:

• Create a new Project with Uno Platform using Visual Studio Template Wizard or the dotnet new command
• Add elements to the C# file, using C# Markup, to define the layout of the application
• Add code to the C# file to implement the application logic using the Model-View-ViewModel (MVVM) pattern
• Use data binding to connect the UI to the application logic

To complete this tutorial you don't need any prior knowledge of the Uno Platform or C#.

[!INCLUDE VS]

Visual Studio

Note

If you don't have the Uno Platform Extension for Visual Studio installed, follow these instructions.

• Launch Visual Studio and click on Create new project on the Start Window. Alternatively, if you're already in Visual Studio, click New, Project from the File menu.

• Type Uno Platform in the search box

• Click Uno Platform App, then Next

• Name the project Counter and click Create

At this point you'll enter the Uno Platform Template Wizard, giving you options to customize the generated application. For this tutorial, we're only going to configure the markup language and the presentation framework.

• Select Blank and click Customize

• Select the Presentation tab and choose MVVM

• Select the Markup tab and choose C# Markup

Before completing the wizard, take a look through each of the sections and see what other options are available. You can always come back and create a new project with different options later. For more information on all the template options, see Using the Uno Platform Template.

• Click Create to complete the wizard

The template will create a new solution with a number of projects. The main project is a class library called Counter which contains the application code. The other projects are platform-specific heads that contain the platform-specific code required to run the application on each platform.

Command Line

Note

If you don't have the Uno Platform dotnet new templates installed, follow dotnet new templates for Uno Platform.

From the command line, run the following command:

dotnet new unoapp -preset blank -presentation mvvm -markup csharp -o Counter

This will create a new folder called Counter containing the new application.

If you want to discover all the options available in the unoapp template, run the following command:

dotnet new unoapp -h

Also, for more information on all the template options, see Using the Uno Platform Template.

---

[!INCLUDE Counter Solution]

[!INCLUDE Main Window]

[!INCLUDE Main Page - C# Markup]

[!INCLUDE Main Page - Layout]

[!INCLUDE Main Page - Image]

[!INCLUDE Main Page - Change Layout]

[!INCLUDE Main Page - Other Elements]

[!INCLUDE View Model]

Data Binding

Now that we have the MainViewModel class, we can update the MainPage to use data binding to connect the UI to the application logic.

• Let's add the DataContext to our page. To do so, add .DataContext(new MainViewModel(), (page, vm) => page before .Background(...). Remember to close the DataContext expression with a ) at the end of the code. It should look similar to the code below:

  this.DataContext(new MainViewModel(), (page, vm) => page
      .Background(ThemeResource.Get<Brush>("ApplicationPageBackgroundThemeBrush"))
      .Content(
          ...
      )
  );

• Update the TextBlock by removing its current text content and replacing it with a binding expression for the Count property of the MainViewModel. Modify the existing Text property with () => vm.Count, txt => $"Counter: {txt}". The adjusted code is as follows:

  new TextBlock()
      .Margin(12)
      .HorizontalAlignment(HorizontalAlignment.Center)
      .TextAlignment(Microsoft.UI.Xaml.TextAlignment.Center)
      .Text(() => vm.Count, txt => $"Counter: {txt}")

• Update the TextBox by binding the Text property to the Step property of the MainViewModel. The Mode of the binding is set to TwoWay so that the Step property is updated when the user changes the value in the TextBox.

  new TextBox()
      .Margin(12)
      .HorizontalAlignment(HorizontalAlignment.Center)
      .TextAlignment(Microsoft.UI.Xaml.TextAlignment.Center)
      .PlaceholderText("Step Size")
      .Text(x => x.Bind(() => vm.Step).TwoWay())

• Update the Button to add a Command property that is bound to the IncrementCommand property of the MainViewModel.

  new Button()
      .Margin(12)
      .HorizontalAlignment(HorizontalAlignment.Center)
      .Command(() => vm.IncrementCommand)
      .Content("Increment Counter by Step Size")

• The final code for MainPage.cs should look like this:

  namespace Counter;
  
  public sealed partial class MainPage : Page
  {
      public MainPage()
      {
          this.DataContext(new MainViewModel(), (page, vm) => page
              .Background(ThemeResource.Get<Brush>("ApplicationPageBackgroundThemeBrush"))
              .Content(
                  new StackPanel()
                      .VerticalAlignment(VerticalAlignment.Center)
                      .Children(
                          new Image()
                              .Margin(12)
                              .HorizontalAlignment(HorizontalAlignment.Center)
                              .Width(150)
                              .Height(150)
                              .Source("ms-appx:///Counter/Assets/logo.png"),
                          new TextBox()
                              .Margin(12)
                              .HorizontalAlignment(HorizontalAlignment.Center)
                              .TextAlignment(Microsoft.UI.Xaml.TextAlignment.Center)
                              .PlaceholderText("Step Size")
                              .Text(x => x.Bind(() => vm.Step).TwoWay()),
                          new TextBlock()
                              .Margin(12)
                              .HorizontalAlignment(HorizontalAlignment.Center)
                              .TextAlignment(Microsoft.UI.Xaml.TextAlignment.Center)
                              .Text(() => vm.Count, txt => $"Counter: {txt}"),
                          new Button()
                              .Margin(12)
                              .HorizontalAlignment(HorizontalAlignment.Center)
                              .Command(() => vm.IncrementCommand)
                              .Content("Increment Counter by Step Size")
                      )
              )
          );
      }
  }

[!INCLUDE View Model]

If you want to see the completed application, you can download the source code from GitHub.