How-To: Navigate in XAML

This topic walks through controlling Navigation from XAML. This includes specifying data that should be attached to the navigation request.

Step-by-steps

Important

This guide assumes you used the template wizard or dotnet new unoapp to create your solution. If not, it is recommended that you follow the instructions for creating an application from the template.

1. Navigation.Request

Navigation can be defined in XAML by placing the Navigation.Request attached property on a specific XAML element. The string value specified in the Navigation.Request is the route to be navigated to. Depending on the type of the XAML element, the Navigation.Request property will attach to an appropriate event in order to trigger navigation. For example, on a Button, the Click event will be used to trigger navigation, where as the SelectionChanged event on a ListView is used. If you place a Navigation.Request property on an static element, such as a Border, Image or TextBlock, the Tapped event will be used to trigger navigation.

Add a new Page to navigate to, SamplePage.xaml, in the UI (shared) project

Add a new class, SampleViewModel, to the class library project

public class SampleViewModel
{
    public SampleViewModel(INavigator navigator)
    {
        _navigator = navigator;
    }

    private readonly INavigator _navigator;
}

In MainPage.xaml update the Button to use the Navigation.Request attached property instead of the Click event handler.
```
<Button Content="Go to SamplePage"
        uen:Navigation.Request="Sample" />
```

Tip

As Navigation.Request attached property exists in the Uno.Extensions.Navigation.UI namespace you will need to import this namespace on the Page element with

<Page x:Class="NavigateInXAML.Views.SamplePage" 
    ...
    xmlns:uen="using:Uno.Extensions.Navigation.UI">

In SamplePage.xaml add a Button, again with the Navigation.Request attached property. The "-" navigation route is used to navigate back.
```
<Button Content="Go Back"
        uen:Navigation.Request="-" />
```

Tip

Whilst this works, it relies on reflection to convert the request path "Sample" to the corresponding view, i.e. SamplePage. It's better to define ViewMap and RouteMap

Add a ViewMap and a RouteMap for the SamplePage into the RegisterRoutes method in the App.xaml.host.cs file

private static void RegisterRoutes(IViewRegistry views, IRouteRegistry routes)
{
    views.Register(
        new ViewMap<ShellControl,ShellViewModel>(),
        new ViewMap<MainPage, MainViewModel>(),
        new ViewMap<SecondPage, SecondViewModel>(),
        new ViewMap<SamplePage, SampleViewModel>()
    );

    routes.Register(
        new RouteMap("", View: views.FindByViewModel<ShellViewModel>() ,
            Nested: new RouteMap[]
            {
                new RouteMap("Main", View: views.FindByViewModel<MainViewModel>()),
                new RouteMap("Second", View: views.FindByViewModel<SecondViewModel>()),
                new RouteMap("Sample", View: views.FindByViewModel<SampleViewModel>()),
    }));
}

2. Navigation.Data

In addition to specifying the route to navigate to, the Navigation.Data attached property can be used to define the data to be attached to the navigation request. The data can be accessed by the view model associated with the route using constructor injection.

Define a record (or class), Widget, that is the type of data that will be attached to the navigation request.
```
public record Widget(string Name, double Weight);
```

Add a property, Widgets, to MainViewModel that returns an array of predefined Widget instances.

public Widget[] Widgets { get; } = new[]
{
    new Widget("NormalSpinner", 5.0),
    new Widget("HeavySpinner",50.0)
};

Replace the Button with a ListView in MainPage.xaml that has the ItemsSource property data bound to the Widgets property.

<StackPanel Grid.Row="1"
            HorizontalAlignment="Center"
            VerticalAlignment="Center">
    <ListView ItemsSource="{Binding Widgets}"
              x:Name="WidgetsList"
              SelectionMode="Single">
        <ListView.ItemTemplate>
            <DataTemplate>
                <StackPanel Orientation="Horizontal"
                            Padding="10">
                    <TextBlock Text="{Binding Name}" />
                    <TextBlock Text="{Binding Age}" />
                </StackPanel>
            </DataTemplate>
        </ListView.ItemTemplate>
    </ListView>
</StackPanel>

Add a Button to the StackPanel on MainPage.xaml that has both Navigation.Request, that specified the navigation route, and the Navigation.Data properties. In this case the Navigation.Data attached property is data bound to the SelectedItem property on the named element WidgetsList (which matches the x:Name set on the previously added ListView)
```
<Button Content="Go to Sample Page"
        uen:Navigation.Request="Sample" 
        uen:Navigation.Data="{Binding SelectedItem, ElementName=WidgetsList}"/>
```

Update SecondViewModel to accept a Widget as the second constructor parameter

public class SampleViewModel
{
    public string Title => "Sample Page";

    public string Name { get; }

    public SampleViewModel(Widget widget)
    {
        Name = widget.Name;
    }
}

Add a TextBlock to SecondPage.xaml that shows the name of the Widget supplied during navigation.

<TextBlock HorizontalAlignment="Center"
           VerticalAlignment="Center">
    <Run Text="Widget Name:" />
    <Run Text="{Binding Name}" />
</TextBlock>

In order for the Widget to be injected into the SampleViewModel during navigation, a DataMap has to be added to the ViewMap
```
new ViewMap<SamplePage, SampleViewModel>(Data: new DataMap<Widget>())
```

3. Navigating To SelectedItem

Instead of having to select an item in the ListView and then clicking on the Button, Navigation can be triggered when the user selects an item in the ListView.

Add the Navigation.Request property to the ListView. The Navigation.Data property is not required as the selected item will automatically be attached to the navigation request. Also remove the SelectionMode property as it is no longer necessary for the ListView to track the selected item.

<ListView ItemsSource="{Binding Widgets}"
          uen:Navigation.Request="Sample">
    <ListView.ItemTemplate>
        <DataTemplate>
            <StackPanel Orientation="Horizontal"
                        Padding="10">
                <TextBlock Text="{Binding Name}" />
                <TextBlock Text="{Binding Age}" />
            </StackPanel>
        </DataTemplate>
    </ListView.ItemTemplate>
</ListView>