I am using prism for my windows phone 8.1 runtime app, i want few conditions to be written in my code on backbutton press, so even though prism will take care of hardware backbutton flow i need to handle it in my local page(either inside cs page or view model), so i override the OnHardwareButtonsBackPressed method in my app.cs page and in my local page i will register and unregister hardware backbutton event in onnavigatedto and onnavigatedfrom method respectively and write my logic, it works fine for me until the app goes background, once if my app goes background and comes back the registered hardware backbutton event is unregistered automatically and from then the back flow is not working.
//App.cs
public sealed partial class App : MvvmAppBase
{
public App()
{
this.InitializeComponent();
}
protected override Task OnLaunchApplicationAsync(LaunchActivatedEventArgs args)
{
NavigationService.Navigate("Main", null);
return Task.FromResult<object>(null);
}
#if WINDOWS_PHONE_APP
protected async override void OnHardwareButtonsBackPressed(object sender, Windows.Phone.UI.Input.BackPressedEventArgs e)
{
var currentFrame = Window.Current.Content as Frame;
var currentView = currentFrame.Content as IView;
if (currentView != null)
{
var backNavigationVM = currentView.DataContext as IBackNavigation;
if ((backNavigationVM == null || backNavigationVM.CanGoBack))
{
base.OnHardwareButtonsBackPressed(sender, e);
}
else
{
e.Handled = true;
}
}
else
{
e.Handled = true;
}
}
#endif
}
//My page.xaml
<storeApps:VisualStateAwarePage
x:Class="BackButtonWithPrism.Views.SecondPage"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:local="using:BackButtonWithPrism.Views"
xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
mc:Ignorable="d"
Background="{ThemeResource ApplicationPageBackgroundThemeBrush}"
xmlns:storeApps="using:Microsoft.Practices.Prism.StoreApps"
xmlns:mvvm="using:Microsoft.Practices.Prism.Mvvm"
mvvm:ViewModelLocator.AutoWireViewModel="True">
<Grid>
<TextBlock Text="SecondPage" FontSize="{StaticResource TextStyleLargeFontSize}" HorizontalAlignment="Center"></TextBlock>
<Grid x:Name="FirstGrid">
<Button HorizontalAlignment="Center" Content="FirstGrid" Click="Button_Click"></Button>
</Grid>
<Grid x:Name="SecondGrid">
<Button HorizontalAlignment="Center" x:Name="btnSecond" Content="SecondGrid"></Button>
</Grid>
</Grid>
</storeApps:VisualStateAwarePage>
//My page.cs
public sealed partial class SecondPage : VisualStateAwarePage
{
public SecondPage()
{
this.InitializeComponent();
this.NavigationCacheMode = NavigationCacheMode.Required;
}
protected async override void OnNavigatedTo(NavigationEventArgs e)
{
FirstGrid.Visibility = Visibility.Visible;
SecondGrid.Visibility = Visibility.Collapsed;
#if WINDOWS_PHONE_APP
Windows.Phone.UI.Input.HardwareButtons.BackPressed += HardwareButtons_BackPressed;
#endif
}
#if WINDOWS_PHONE_APP
private async void HardwareButtons_BackPressed(object sender, Windows.Phone.UI.Input.BackPressedEventArgs e)
{
if (FirstGrid.Visibility == Visibility.Collapsed)
{
e.Handled = true;
FirstGrid.Visibility = Visibility.Visible;
SecondGrid.Visibility = Visibility.Collapsed;
}
else
{
Frame currentFrame = Window.Current.Content as Frame;
if (currentFrame == null)
{
return;
}
else if (currentFrame.CanGoBack)
{
currentFrame.GoBack();
e.Handled = true;
}
}
}
#endif
protected async override void OnNavigatedFrom(NavigationEventArgs e)
{
Windows.Phone.UI.Input.HardwareButtons.BackPressed -= HardwareButtons_BackPressed;
}
private void Button_Click(object sender, RoutedEventArgs e)
{
FirstGrid.Visibility = Visibility.Collapsed;
SecondGrid.Visibility = Visibility.Visible;
}
}
//My Page ViewModel:
public class SecondPageViewModel : ViewModel, IBackNavigation
{
public bool CanGoBack
{
get;
set;
}
}
here all my logic i have written in my cs page instead of writting in viewmodel but i ill do it later.
