Tip Calculator A Wpf UI Project

We started with the goal of creating an app to help calculate what tip to leave in a restaurant

We had a plan to produce a UI based on this concept:

Sketch

To satisfy this we built a 'Core' Portable Class Library project which contained:

our 'business logic' - ICalculation
our ViewModel - TipViewModel
our App which contains the application wiring, including the start instructions.

We've then added User Interfaces - for Xamarin.Android, Xamarin.iOS, Windows Universal Apps, Windows Phone Silverlight and Windows Store:

Android

For our next project, let's shift to Windows Desktop - via WPF - Windows Presentation Framework.

Here we'll build up a new project 'from empty', just as we did for the Core, Android, iOS, Windows Universal Apps, Windows Phone Silverlight and Windows Store projects.

Obviously, to work with WPF, you will need to be working on the PC with Visual Studio

Create a new WPF Project

Add a new project to your solution - a 'WPF Application' with name TipCalc.UI.Wpf

Important - make sure this is at least .Net4.5 - as this is the version required for PCL Profile259 - goodbye, XP!

Within this, you'll find the normal Wpf application constructs:

the 'Properties' folder with the 'AssemblyInfo' file, some resources and a settings file
the 'App.Config' configuration file
the App.Xaml 'application' object
the MainWindow.Xaml and MainWindows.Xaml.cs files that define the default Window for this app

Keep MainWindow.xaml

We do actually want a MainWindow for this app :)

Install MvvmCross

In the Package Manager Console, enter...

Install-Package MvvmCross.HotTuna.MvvmCrossLibraries

Add a reference to TipCalc.Core.csproj

Add a reference to your TipCalc.Core project - the project we created in the last step which included:

your Calculation service,
your TipViewModel
your App wiring.

Add a Setup class

Just as we said during the construction of the other UI projects Every MvvmCross UI project requires a Setup class

This class sits in the root namespace (folder) of our UI project and performs the initialisation of the MvvmCross framework and your application, including:

the Inversion of Control (IoC) system
the MvvmCross data-binding
your App and its collection of ViewModels
your UI project and its collection of Views

Most of this functionality is provided for you automatically. Within your Wpf UI project all you have to supply is:

your App - your link to the business logic and ViewModel content

For TipCalc here's all that is needed in Setup.cs:

using System.Windows.Threading;
using Cirrious.MvvmCross.ViewModels;
using Cirrious.MvvmCross.Wpf.Platform;
using Cirrious.MvvmCross.Wpf.Views;

namespace TipCalc.UI.Wpf
{
    public class Setup : MvxWpfSetup
    {
        public Setup(Dispatcher uiThreadDispatcher, IMvxWpfViewPresenter presenter) : base(uiThreadDispatcher, presenter)
        {
        }

        protected override IMvxApplication CreateApp()
        {
            return new Core.App();
        }
    }
}

Modify the App.xaml.cs to use Setup

There are other lifecycles and display techniques that you can use to write Wpf apps.

However, here we will just use a 'one window with one view' approach.

To achieve this, add some lines to the WPF App class that:

provide a private flag to determine if setup has already been done
```
  private bool _setupComplete = false;
```

perform the setup - using a Simple presenter based on MainWindow

  private void DoSetup()
  {
      var presenter = new MvxSimpleWpfViewPresenter(MainWindow);

      var setup = new Setup(Dispatcher, presenter);
      setup.Initialize();

      var start = Mvx.Resolve<IMvxAppStart>();
      start.Start();

      _setupComplete = true;
  }

override the OnActivated event to perform this startup

  protected override void OnActivated(System.EventArgs e)
  {
      if (!_setupComplete)
          DoSetup();

      base.OnActivated(e);
  }

After you've done this your App.xaml.cs might look like:

using System.Windows;
using Cirrious.CrossCore.IoC;
using Cirrious.MvvmCross.ViewModels;
using Cirrious.MvvmCross.Wpf.Views;

namespace TipCalc.UI.Wpf
{
    public partial class App : Application
    {
        private bool _setupComplete = false;

        private void DoSetup()
        {
            var presenter = new MvxSimpleWpfViewPresenter(MainWindow);

            var setup = new Setup(Dispatcher, presenter);
            setup.Initialize();

            var start = Mvx.Resolve<IMvxAppStart>();
            start.Start();

            _setupComplete = true;
        }

        protected override void OnActivated(System.EventArgs e)
        {
            if (!_setupComplete)
                DoSetup();

            base.OnActivated(e);
        }
    }
}

Add your View

Create the UserControl

Create a Views folder

Within this folder, add a new 'User Control (WPF)' and call it TipView.xaml

The page will generate:

TipView.xaml
TipView.xaml.cs

Turn TipView into the MvvmCross View for TipViewModel

Open the TipView.xaml.cs file.

Change the class to inherit from MvxWpfView

public partial class TipView : MvxWpfView

To link TipView to TipViewModel create a public new TipViewModel ViewModel property - exactly as you did in Xamarin.Android, Xamarin.iOS, WindowsPhone and WindowsStore:

public new TipViewModel ViewModel
{
    get { return (TipViewModel) base.ViewModel; }
    set { base.ViewModel = value; }
}

Altogether this looks like:

using Cirrious.MvvmCross.Wpf.Views;
using TipCalc.Core.ViewModels;

namespace TipCalc.UI.Wpf.Views
{
    public partial class TipView : MvxWpfView
    {
        public new TipViewModel ViewModel
        {
            get { return (TipViewModel)base.ViewModel; }
            set { base.ViewModel = value; }
        }

        public TipView()
        {
            InitializeComponent();
        }
    }
}

Edit the XAML layout

Double click on the XAML file

This will open the XAML editor within Visual Studio.

Just as with the WindowsPhone and WindowsStore, I won't go into much depth at all here about how to use the XAML or do the Windows data-binding. I'm assuming most readers are already coming from at least a little XAML background.

Change the root node from:

<UserControl 
         ...
</UserControl>

to:

<views:MvxWpfView 
         xmlns:views="clr-namespace:Cirrious.MvvmCross.Wpf.Views;assembly=Cirrious.MvvmCross.Wpf"
         ...
</views:MvxWpfView>

To add the XAML user interface for our tip calculator, we will add exactly the same XAML as we added inside the ContentPanel grid for the WindowsStore example. This includes:

a StackPanel container, into which we add:
- some TextBlock static text
- a bound TextBox for the SubTotal
- a bound Slider for the Generosity
- a bound TextBlock for the Tip

This will produce finished XAML like:

<views:MvxWpfView 
             xmlns:views="clr-namespace:Cirrious.MvvmCross.Wpf.Views;assembly=Cirrious.MvvmCross.Wpf"
             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
             x:Class="TipCalc.UI.Wpf.Views.TipView">
    <StackPanel>
        <TextBlock
                    Text="SubTotal"
                    />
        <TextBox 
                    Text="{Binding SubTotal, Mode=TwoWay}" 
                    />

        <TextBlock
                    Text="Generosity"
                    />
        <Slider 
                    Value="{Binding Generosity, Mode=TwoWay}" 
                    SmallChange="1" 
                    LargeChange="10" 
                    Minimum="0" 
                    Maximum="100" />

        <TextBlock
                    Text="Tip"
                    />
        <TextBlock 
                    Text="{Binding Tip}" 
                    />
    </StackPanel>
</views:MvxWpfView>

Note that in XAML, OneWay binding is generally the default. To provide TwoWay binding we explicitly add Mode to our binding expressions: e.g. Value="{Binding Generosity,Mode=TwoWay}"

In the designer, this will look like:

Designer

The Wpf UI is complete!

At this point you should be able to run your application.

When it starts... you should see:

Designer

This seems to work perfectly, although you may notice that if you edit the value in the SubTotal TextBox then you rest of the display does not correctly update.

This is a View concern - it is a UI problem. So we can fix it just in the Wpf UI code - just as we did in the WindowsPhone and WindowsStore examples.

Moving on...

There's more we could do to make this User Interface nicer and to make the app richer... but for this first application, we will leave it here for now.

And actually... that's the end of our journey through this first app.

One day soon there will be more steps - a step for Mac desktop, a step for XBox, a step for TV, etc - but for now this is the end.

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