Tip Calc Windows Store 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:

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 then added User Interfaces for Xamarin.Android, Xamarin.iOS, Universal Windows Apps and Windows Phone Silverlight:

For our next project, let's look at Windows 8.0.

To create a Windows 8.0 MvvmCross UI, you can use the Visual Studio project template wizards, but here we'll instead build up a new project 'from empty', just as we did for the Core and other UI projects.

Create a new Windows 8.0 Project

To create a Windows 8.0 app, you'll need to use Visual Studio 2012. Add a new project to your solution - a 'Blank App (XAML)' application with name TipCalc.UI.WindowsStore

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

• the 'Properties' folder with just the 'AssemblyInfo' file
• the 'Assets' folder
• the 'Common' folder
• the App.Xaml 'application' object
• the MainPage.Xaml and MainPage.Xaml.cs files that define the default Page for this app
• the 'Package.appxmanifest' configuration file
• the debug private key for your development

Delete MainPage.xaml

No-one really needs a MainPage :)

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 Android, iOS and WO construction 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 WindowsStore 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 Cirrious.MvvmCross.ViewModels;
using Cirrious.MvvmCross.WindowsStore.Platform;
using Windows.UI.Xaml.Controls;

namespace TipCalc.UI.WindowsStore
{
    public class Setup : MvxStoreSetup
    {
        public Setup(Frame rootFrame) : base(rootFrame)
        {
        }

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

Modify the App.xaml.cs to use Setup

Your App.xaml.cs provides the WindowsStore 'main application' object - an object which owns the User Interface and receives some callbacks from the operating system during some key events in your application's lifecycle.

To modify this App.xaml.cs for MvvmCross, we need to:

• modify the OnLaunched callback

• remove these lines

           if (!rootFrame.Navigate(typeof(MainPage), args.Arguments))
           {
               throw new Exception("Failed to create initial page");
           }
  

• add these lines to allow it to create Setup, and to then initiate the IMvxAppStart Start navigation

       var setup = new Setup(rootFrame);
       setup.Initialize();
  
       var start = Mvx.Resolve<IMvxAppStart>();
       start.Start();
  

To do this, you will need to add these using lines:

using Cirrious.CrossCore.IoC;
using Cirrious.MvvmCross.ViewModels;

Add your View

Create an initial Page

Create a Views folder

Within this folder, add a new 'Basic Page' and call it TipView.xaml

You will be asked if you want to add the missing 'Common' files automatically in order to support this 'Basic Page' - answer Yes

The page will generate:

• TipView.xaml
• TipView.xaml.cs

Convert LayoutAwarePage into an MvvmCross base view

Change LayoutAwarePage so that it inherits from MvxStorePage

Change:

public class LayoutAwarePage : Page

to:

public class LayoutAwarePage : MvxStorePage

This requires the addition of:

using Cirrious.MvvmCross.WindowsStore.Views;

Persuade LayoutAwarePage to cooperate more reasonably with the MvxStorePage base class

Either remove the region:

    #region Process lifetime management
    
    // all sorts of 'stuff' including
    //  OnNavigatedTo
    //  OnNavigatedFrom
    //  LoadState
    //  SaveState

    #endregion 

Or change the OnNavigatedTo and OnNavigatedFrom methods so that they call their base class implementations:

base.OnNavigatedTo(e);

and

base.OnNavigatedFrom(e);

Turn TipView into the MvvmCross View for TipViewModel

Open the TipView.cs file.

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

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

Altogether this looks like:

using TipCalc.Core.ViewModels;

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

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

Edit the XAML layout

Double click on the XAML file

This will open the XAML editor within Visual Studio.

Just as with the Universal Windows Apps and Windows Phone Silverlight, 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.

To add the XAML user interface for our tip calculator, we will add a StackPanel before the existing <VisualStateManager.VisualStateGroups> XAML node.

This StackPanel will include almost exactly the same XAML as we added to the Windows Phone Silverlight example - only the Style attributes are removed:

• 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 XAML like:

    <Grid x:Name="ContentPanel" Grid.Row="1" Margin="12,0,12,0">
        <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>
    </Grid>

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:

The Store UI is complete!

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

When it starts... you should see:

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 WindowsStore UI code - just as we did in the WindowsPhone example.

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.

Let's move on to one final piece of Windows!