Dispatch function accessible in App projects

docs/update.md

@@ -168,4 +168,77 @@ let update msg model =
     match msg with
     | TakePicture -> model, (Cmd.ofAsyncMsgOption takePictureCmd)
     | PictureTaken -> ...
+```
+
+Platform-specific dispatch
+-----
+
+Some platform-specific features (like deep linking, memory warnings, ...) are not available in Xamarin.Forms, and need you to implement them in the corresponding app projet.  
+In this case, you might want to dispatch a message from the app project to Fabulous to start a shared logic between platforms (to warn user, ...).
+
+To allow for this kind of use case, the `dispatch` function is exposed as a `Dispatch(msg)` method by the `ProgramRunner`. By default this runner is not accessible, but you can make a read-only property to let apps access it.
+
+```fsharp
+type App() as app =
+    inherit Application()
+
+    let runner =
+        Program.mkProgram init update view
+        |> Program.runWithDynamicView app
+
+    member __.Program = runner // Add this line
+```
+
+Once done, you can access it in the app project
+
+- Android
+```fsharp
+[<Activity>]
+type MainActivity() =
+    inherit FormsApplicationActivity()
+
+    // Store the App instance
+    let mutable _app: App option = None
+
+    override this.OnCreate (bundle: Bundle) =
+        base.OnCreate (bundle)
+
+        Forms.Init (this, bundle)
+
+        // Initialize the app and store its reference
+        let app = new App()
+        this.LoadApplication(app)
+        _app <- Some app
+
+    override this.OnTrimMemory(level) =
+        // If the app is initialized, dispatch the message
+        match _app with
+        | Some app -> app.Program.Dispatch(Msg.ReceivedLowMemoryWarning)
+        | None -> ()
+```
+
+- iOS
+```fsharp
+[<Register("AppDelegate")>]
+type AppDelegate () =
+    inherit FormsApplicationDelegate ()
+
+    // Store the App instance
+    let mutable _app: App option = None
+
+    override this.FinishedLaunching (uiApp, options) =
+        Forms.Init()
+
+        // Initialize the app and store its reference
+        let app = new AllControls.App()
+        this.LoadApplication (app)
+        _app <- Some app
+
+        base.FinishedLaunching(uiApp, options)
+
+    override this.ReceiveMemoryWarning(uiApp) =
+        // If the app is initialized, dispatch the message
+        match _app with
+        | Some app -> app.Program.Dispatch(Msg.ReceivedLowMemoryWarning)
+        | None -> ()
 ```

samples/AllControls/AllControls/AllControls.fs

@@ -1,4 +1,4 @@
-// Copyright 2018 Fabulous contributors. See LICENSE.md for license.
+// Copyright 2018 Fabulous contributors. See LICENSE.md for license.
 namespace AllControls
 
 open System
@@ -90,6 +90,7 @@ type Msg =
     | AnimationPoked3
     | SetCarouselCurrentPage of int
     | SetTabbed1CurrentPage of int
+    | ReceivedLowMemoryWarning
 
 [<AutoOpen>]
 module MyExtension = 
@@ -235,6 +236,14 @@ module App =
             { model with CarouselCurrentPageIndex = index }
         | SetTabbed1CurrentPage index ->
             { model with Tabbed1CurrentPageIndex = index }
+        | ReceivedLowMemoryWarning ->
+            Application.Current.MainPage.DisplayAlert("Low memory!", "Cleaning up data...", "OK") |> ignore
+            { model with
+                EditorText = ""
+                EntryText = ""
+                Placeholder = ""
+                Password = ""
+                SearchTerm = "" }
 
     let pickerItems = 
         [| ("Aqua", Color.Aqua); ("Black", Color.Black);
@@ -761,3 +770,5 @@ type App () as app =
         Program.mkSimple App.init App.update App.view
         |> Program.withConsoleTrace
         |> Program.runWithDynamicView app
+
+    member __.Program = runner

samples/AllControls/Droid/MainActivity.fs

@@ -1,4 +1,4 @@
-// Copyright 2018 Fabulous contributors. See LICENSE.md for license.
+// Copyright 2018 Fabulous contributors. See LICENSE.md for license.
 namespace AllControls.Droid
 
 open System
@@ -15,10 +15,20 @@ open Xamarin.Forms.Platform.Android
 [<Activity (Label = "AllControls.Droid", Icon = "@drawable/icon", MainLauncher = true, ConfigurationChanges = (ConfigChanges.ScreenSize ||| ConfigChanges.Orientation))>]
 type MainActivity() =
     inherit FormsApplicationActivity()
+
+    let mutable _app: AllControls.App option = None
+
     override this.OnCreate (bundle: Bundle) =
         base.OnCreate (bundle)
 
         Xamarin.Forms.Forms.Init (this, bundle)
 
-        this.LoadApplication (new AllControls.App ())
+        let app = new AllControls.App()
+        this.LoadApplication(app)
+        _app <- Some app
+
+    override this.OnTrimMemory(level) =
+        match _app with
+        | Some app -> app.Program.Dispatch(AllControls.Msg.ReceivedLowMemoryWarning)
+        | None -> ()
 

samples/AllControls/iOS/AppDelegate.fs

@@ -1,20 +1,31 @@
-// Copyright 2018 Fabulous contributors. See LICENSE.md for license.
+// Copyright 2018 Fabulous contributors. See LICENSE.md for license.
 namespace iOS
 
 open System
 open UIKit
 open Foundation
 open Xamarin.Forms
 open Xamarin.Forms.Platform.iOS
+open AllControls
 
 [<Register ("AppDelegate")>]
 type AppDelegate () =
     inherit FormsApplicationDelegate ()
 
-    override this.FinishedLaunching (app, options) =
+    let mutable _app: AllControls.App option = None
+
+    override this.FinishedLaunching (uiApp, options) =
         Forms.Init()
-        this.LoadApplication (new AllControls.App())
-        base.FinishedLaunching(app, options)
+        let app = new AllControls.App()
+        this.LoadApplication (app)
+        _app <- Some app
+
+        base.FinishedLaunching(uiApp, options)
+
+    override this.ReceiveMemoryWarning(uiApp) =
+        match _app with
+        | Some app -> app.Program.Dispatch(AllControls.Msg.ReceivedLowMemoryWarning)
+        | None -> ()
 
 module Main =
     [<EntryPoint>]

src/Fabulous.Core/ElmishProgram.fs

@@ -1,4 +1,4 @@
-// Copyright 2018 Elmish and Fabulous contributors. See LICENSE.md for license.
+// Copyright 2018 Elmish and Fabulous contributors. See LICENSE.md for license.
 namespace Fabulous.Core
 
 open System
@@ -122,7 +122,9 @@ type ProgramRunner<'model, 'msg>(app: Application, program: Program<'model, 'msg
     member __.InitialMainPage = mainPage
 
     member __.CurrentModel = lastModel 
-
+
+    member __.Dispatch(msg) = dispatch msg
+
     member runner.ChangeProgram(newProgram: Program<obj, obj, obj -> (obj -> unit) -> ViewElement>) : unit  =
         Device.BeginInvokeOnMainThread(fun () -> 
             // TODO: transmogrify the model