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Tip Calc A Universal Windows App UI Project

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Michel van den Berg edited this page May 4, 2015 · 6 revisions

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 then added two User Interfaces - for Xamarin.Android and Xamarin.iOS.

We'll now take a look at Windows and Windows Phone using Universal Windows Apps.

A Universal Windows App is actually a set of three projects. A Windows Phone 8.1 WinRT project, A Windows 8.1 project and a Shared project. Unlike normal projects, the Shared project does not build to an assembly. It's actually a set of files which are accessible within the Windows Phone and Windows projects as if they existed within those projects. If you are familiar with file linking, it's pretty much the same thing with an improved UI.

You could follow all the steps below creating two separate Windows 8.1 and Windows Phone 8.1 RT projects but the code which gets placed in the Universal Shared project gets placed in both the Windows 8.1 and the Windows Phone 8.1 RT projects instead.

Obviously, to work with Windows and Windows Phone, we will need to switch back to working on the PC with Visual Studio.

Create the new Universal Windows Apps Projects

Add a new project to your solution - a 'Blank App (Universal Apps)' application with name TipCalc.UI.WindowsCommon

Note that three projects have been added to your solution. TipCalc.UI.WindowsCommon.Windows, TipCalc.UI.WindowsCommon.WindowsPhone and TipCalc.UI.WindowsCommon.Shared.

Within the WindowsCommon.Windows and WindowsCommon.WindowsPhone projects, you'll find the normal Universal Windows App UI application constructs:

  • the 'Assets' folder, which contains the default images
  • 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 (WindowsCommon.Windows project only)

Within the Shared project, you'll find the normal Universal Windows App shared application constructs:

  • the App.Xaml 'application' object

Delete MainPage.xaml

No-one really needs a MainPage :)

This needs to be removed from both the WindowsCommon.Windows and WindowsCommon.WindowsPhone projects.

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 WindowsCommon.Windows and WindowsCommon.WindowsPhone UI project all you have to supply are:

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

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

using Windows.UI.Xaml.Controls;
using Cirrious.MvvmCross.ViewModels;
using Cirrious.MvvmCross.WindowsCommon.Platform;

namespace TipCalc.UI.WindowsCommon
{
    public class Setup : MvxWindowsSetup
    {
        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 Universal Windows App '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;
using Cirrious.MvvmCross.ViewModels;

Add your View

Create an initial Page for the WindowsCommon.Windows project

Create a Views folder in the WindowsCommon.Windows project

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

A Common folder will be added containing:

  • NavigationHelper.cs
  • ObservableDictionary.cs
  • RelayCommand.cs
  • SuspensionManager.cs

Convert TipView into an MvvmCross base view

Change TipView so that it inherits from MvxWindowsPage

Change:

public class TipView : Page

to:

public class TipView : MvxWindowsPage

This requires the addition of:

using Cirrious.MvvmCross.WindowsCommon.Views;

Persuade LayoutAwarePage to cooperate more reasonably with the MvxWindowsPage base class

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 and Xamarin.iOS:

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

Remove the LoadState and SaveState methods.

Altogether this looks like:

using Cirrious.MvvmCross.WindowsCommon.Views;
using TipCalc.Core.ViewModels;
using TipCalc.UI.WindowsCommon.Common;
using Windows.UI.Xaml.Navigation;

// The Basic Page item template is documented at http://go.microsoft.com/fwlink/?LinkId=234237

namespace TipCalc.UI.WindowsCommon.Views
{
	/// <summary>
	/// A basic page that provides characteristics common to most applications.
	/// </summary>
	public sealed partial class TipView : MvxWindowsPage
	{
		public new TipViewModel ViewModel
		{
			get { return (TipViewModel)base.ViewModel; }
			set { base.ViewModel = value; }
		}

		private NavigationHelper navigationHelper;
		private ObservableDictionary defaultViewModel = new ObservableDictionary();

		public ObservableDictionary DefaultViewModel
		{
			get { return this.defaultViewModel; }
		}

		public NavigationHelper NavigationHelper
		{
			get { return this.navigationHelper; }
		}


		public TipView()
		{
			this.InitializeComponent();
			this.navigationHelper = new NavigationHelper(this);
		}

		protected override void OnNavigatedTo(NavigationEventArgs e)
		{
			base.OnNavigatedTo(e);
			navigationHelper.OnNavigatedTo(e);
		}

		protected override void OnNavigatedFrom(NavigationEventArgs e)
		{
			base.OnNavigatedFrom(e);
			navigationHelper.OnNavigatedFrom(e);
		}
	}
}

Edit the XAML layout

Double click on the XAML file

This will open the XAML editor within Visual Studio.

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 make the XAML inheritance match the MvxWindowsPage inheritance, change the outer root node of the Xaml file from:

<Page 
    ... >
    <!-- content -->
</Page>

to:

<views:MvxWindowsPage
    xmlns:views="using:Cirrious.MvvmCross.WindowsCommon.Views"
    ... >
    <!-- content -->
</views:MvxWindowsPage>

To add the XAML user interface for our tip calculator, we will add a ContentPanel Grid just above the final </Grid> in the existing XAML. This will contain:

  • 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, UpdateSourceTrigger=PropertyChanged}" 
                />

            <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:

Designer

Create an initial Page for the WindowsCommon.WindowsPhone project

Create a Views folder in the WindowsCommon.WindowsPhone project

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

A Common folder will be added containing:

  • NavigationHelper.cs
  • ObservableDictionary.cs
  • RelayCommand.cs
  • SuspensionManager.cs

Convert TipView into an MvvmCross base view

Change TipView so that it inherits from MvxWindowsPage

Change:

public class TipView : Page

to:

public class TipView : MvxWindowsPage

This requires the addition of:

using Cirrious.MvvmCross.WindowsCommon.Views;

Persuade LayoutAwarePage to cooperate more reasonably with the MvxWindowsPage base class

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 and Xamarin.iOS:

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

Note: You can also use the generic view class MvxWindowsPage<TViewModel> where you can provide a viewmodel generic parameter, which will already have such a type-specific ViewModel property.

Remove the NavigationHelper_LoadState and NavigationHelper_SaveState methods.

Altogether this looks like:

using Cirrious.MvvmCross.WindowsCommon.Views;
using TipCalc.Core.ViewModels;
using TipCalc.UI.WindowsCommon.Common;
using Windows.UI.Xaml.Navigation;

namespace TipCalc.UI.WindowsCommon.Views
{
	public sealed partial class TipView : MvxWindowsPage
	{
		public new TipViewModel ViewModel
		{
			get { return (TipViewModel)base.ViewModel; }
			set { base.ViewModel = value; }
		}
		
		private NavigationHelper navigationHelper;
		private ObservableDictionary defaultViewModel = new ObservableDictionary();

		public TipView()
		{
			this.InitializeComponent();

			this.navigationHelper = new NavigationHelper(this);
		}

		public NavigationHelper NavigationHelper
		{
			get { return this.navigationHelper; }
		}

		public ObservableDictionary DefaultViewModel
		{
			get { return this.defaultViewModel; }
		}

		protected override void OnNavigatedTo(NavigationEventArgs e)
		{
			base.OnNavigatedTo(e);
			this.navigationHelper.OnNavigatedTo(e);
		}

		protected override void OnNavigatedFrom(NavigationEventArgs e)
		{
			base.OnNavigatedFrom(e);
			this.navigationHelper.OnNavigatedFrom(e);
		}
	}
}

Edit the XAML layout

Double click on the XAML file

This will open the XAML editor within Visual Studio.

Again, 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 make the XAML inheritance match the MvxWindowsPage inheritance, change the outer root node of the Xaml file from:

<Page 
    ... >
    <!-- content -->
</Page>

to:

<views:MvxWindowsPage
    xmlns:views="using:Cirrious.MvvmCross.WindowsCommon.Views"
    ... >
    <!-- content -->
</views:MvxWindowsPage>

To add the XAML user interface for our tip calculator, we will add a ContentPanel Grid in place of the ContentRoot Grid in the existing XAML.

This Content Panel will include exactly the same XAML as we added to the WindowsCommon.WindowsPhone project except for the margins:

  • 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="19,9.5,19,0">
        <StackPanel>
            <TextBlock
                Text="SubTotal"
                />
            <TextBox 
                Text="{Binding SubTotal, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}" 
                />

            <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:

Designer

The navigation cache

Universal Windows Phone apps seem to differ from Silverlight Windows Phone apps in that the default page navigation cache mechanism has changed. While Silverlight Windows Phone apps have built-in support for caching pages in forward/backward navigation, universal Windows Phone apps do not and need the NavigationHelper class and setting the NavigationCacheMode property of a Page to "Required" to provide this. This tutorial already showed you how to make use of the NavigationHelper and it is recommended that you do this even if you plan not to cache a view.

If you do enable caching by setting the NavigationCacheMode property of a Page to "Required" and navigate backwards or forwards, the view is retrieved from the cache. This includes the ViewModel property of the view. While this doesn't create a problem when navigating backwards, it does when you navigate forward! If you already have cached a view with a particular state (loading from the init parameters into the viewmodel), that state is also retrieved from the cache and you'll end up with a view with an 'old' viewmodel state.

To counter this, you must set the viewmodel to null when navigating to a page:

        protected override void OnNavigatedTo(NavigationEventArgs e)
        {
            if (e.NavigationMode == NavigationMode.New)
                ViewModel = null;

            base.OnNavigatedTo(e);
            this.navigationHelper.OnNavigatedTo(e);
        }

The Universal Windows App is complete!

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

When you run the WindowsCommon.Windows project... you should see:

v1

When you run the WindowsCommon.WindowsPhone project... you should see:

v1

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 look at an alternative way of building Windows Phone apps...

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