Back button support for Dialogs

docs/navigation/backbutton.md

@@ -13,4 +13,6 @@ public class MainActivity : FormsAppCompatActivity
         PopupPlugin.OnBackPressed();
     }
 }
-```
+```
+
+The PopupPlugin.OnBackPressed will check to see if the currently displayed page is PopupDialogContainer. If it is it will call all of the same Dialog API's that you would expect, while using the Navigation Service for all of your other pages and PopupPages.

src/Prism.Plugin.Popups/Dialogs/PopupDialogContainer.cs

@@ -1,8 +1,10 @@
-using Rg.Plugins.Popup.Pages;
+using System;
+using Rg.Plugins.Popup.Pages;
 
 namespace Prism.Plugin.Popups.Dialogs
 {
     internal class PopupDialogContainer : PopupPage
     {
+        public Action RequestClose { get; set; }
     }
 }

src/Prism.Plugin.Popups/Dialogs/PopupDialogService.cs

@@ -115,6 +115,8 @@ void DialogAware_RequestClose(IDialogParameters outParameters)
                     popupPage.BackgroundClicked += CloseOnBackgroundClicked;
                 }
 
+                popupPage.RequestClose = () => DialogAware_RequestClose(null);
+
                 Action<IDialogParameters> closeCallback = closeOnBackgroundTapped ? DialogAware_RequestClose : p => { };
                 PushPopupPage(popupPage, view, closeCallback, animated);
             }
@@ -124,7 +126,7 @@ void DialogAware_RequestClose(IDialogParameters outParameters)
             }
         }
 
-        private static PopupPage CreatePopupPageForView(BindableObject view)
+        private static PopupDialogContainer CreatePopupPageForView(View view)
         {
             var popupPage = new PopupDialogContainer();
 

src/Prism.Plugin.Popups/PopupPlugin.cs

@@ -1,9 +1,10 @@
-#if MONOANDROID
-using System;
+using System;
+using System.Linq;
 using System.Threading;
 using Prism.Common;
 using Prism.Ioc;
 using Prism.Navigation;
+using Prism.Plugin.Popups.Dialogs;
 using Rg.Plugins.Popup.Contracts;
 
 namespace Prism.Plugin.Popups
@@ -23,10 +24,23 @@ public static async void OnBackPressed()
             try
             {
                 var container = ContainerLocator.Container;
-                var popupNavigation = container.Resolve<IPopupNavigation>();
-                var appProvider = container.Resolve<IApplicationProvider>();
+                if (container is null)
+                {
+                    Console.WriteLine("Android back button pressed before Prism has initialized.");
+                    return;
+                }
+
+                var popupNavigation = container.Resolve<IPopupNavigation>(); 
+                if (popupNavigation.PopupStack.Count > 0 &&
+                    popupNavigation.PopupStack.LastOrDefault() is PopupDialogContainer dialog)
+                {
+                    dialog.RequestClose.Invoke();
+                    return;
+                }
 
+                var appProvider = container.Resolve<IApplicationProvider>();
                 var topPage = PopupUtilities.TopPage(popupNavigation, appProvider);
+
                 var navService = container.Resolve<INavigationService>(PrismApplicationBase.NavigationServiceName);
                 if (navService is IPageAware pa)
                 {
@@ -44,4 +58,3 @@ public static async void OnBackPressed()
         }
     }
 }
-#endif

src/Prism.Plugin.Popups/Prism.Plugin.Popups.csproj

@@ -11,11 +11,18 @@
   </PropertyGroup>
 
   <ItemGroup>
+    <Compile Remove="PopupPlugin.cs" />
+    <None Include="PopupPlugin.cs" />
     <None Include="ReadMe.txt" 
           Pack="True"
           PackagePath="." />
   </ItemGroup>
 
+  <ItemGroup Condition="$(TargetFramework.StartsWith('MonoAndroid'))">
+    <None Remove="PopupPlugin.cs" />
+    <Compile Include="PopupPlugin.cs" />
+  </ItemGroup>
+
   <ItemGroup>
     <PackageReference Include="Rg.Plugins.Popup" Version="2.0.0.10" />
     <PackageReference Include="Prism.Forms" Version="8.0.0.1909" />