How-To: Navigate Between Pages

This topic covers using Navigation to navigate between two pages using frame-based navigation.

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 Creating an application with Uno.Extensions article for creating an application from the template.

1. Navigating to a New Page

Add a new Page to navigate to, SamplePage.xaml, in the UI (shared) project
In MainPage.xaml replace the existing Button with the following XAML, which includes a handler for the Click event
```
<Button Content="Go to SamplePage"
        Click="GoToSamplePageClick" />
```
In the GoToSamplePageClick method, use the Navigator extension method to get a reference to an INavigator instance and call NavigateViewAsync to navigate to the SamplePage. This will push a new instance of the SamplePage onto the current Frame, pushing the MainPage to the back-stack.
```
private void GoToSamplePageClick(object sender, RoutedEventArgs e)
{
    _ = this.Navigator()?.NavigateViewAsync<SamplePage>(this);
}
```

2. Navigating Back to the Previous Page

In SamplePage.xaml add a Button with a handler for the Click event
```
<Button Content="Go Back"
        Click="GoBackClick" />
```
Again, use the Navigator extension method to access the INavigator instance and call NavigateBackAsync. This will cause the frame to navigate to the previous page on the back-stack and releasing the SamplePage instance.
```
private void GoBackClick(object sender, RoutedEventArgs e)
{
    _ = this.Navigator()?.NavigateBackAsync(this);
}
```

3. Defining ViewMap and RouteMap

At this point, if you inspect the Output window you'll see a line that says something similar to: For better performance (avoid reflection), create mapping for for path 'Sample', view 'SamplePage', view model This warning exists because Navigation uses reflection as a fallback mechanism to associate types and the corresponding navigation route. This can be resolved by specifying a ViewMap and a RouteMap for the SamplePage to eliminate the need for reflection

Update 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>()
        );

    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.FindByView<SamplePage>()),
            }));
}

4. Associating a View Model

By defining a ViewMap that associates a view with a view model, an instance of the view model can dynamically be created and is subsequently set as the DataContext on the view that's navigated to.

Create a new class SampleViewModel in the ViewModels folder of the class library project

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

Update ViewMap in App.xaml.host.cs to include SampleViewModel
```
new ViewMap<SamplePage, SampleViewModel>()
```
Add TextBlock to the SamplePage.xaml and data bind to the Title property
```
<TextBlock Text="{Binding Title}" />
```

5. Navigating via View Models

The Navigation code can be moved from the SamplePage.cs code-behind file to the SampleViewModel.

Update SampleViewModel to take a constructor dependency on INavigator and add a GoBack method that will call the NavigateBackAsync method

private readonly INavigator _navigator;
public SampleViewModel(INavigator navigator)
{
    _navigator = navigator;
}

public Task GoBack()
{
    return _navigator.NavigateBackAsync(this);
}

In order to use x:Bind to invoke the GoBack method on the SampleViewModel the SamplePage needs to expose a property that returns the DataContext as a SampleViewModel.
```
public SampleViewModel? ViewModel  => DataContext as SampleViewModel;

public SamplePage()
{
    this.InitializeComponent();
}
```

Update the Button in SamplePage.xaml to set the Click method to x:Bind to the GoBack method

<Button Content="Go Back (View Model)"
        Click="{x:Bind ViewModel.GoBack}" />