Animations in Xamarin Forms (XF)

(Part 7 of the Panzer General Portable Project)

Granted, there are not a lot of animations in Panzer General – which is one of the reasons I thought it would be a good candidate for Fabulous and XF.  However, there is 1 place where there is a 6 frame animation – when there is a battle and a unit takes damage.  The images look like this:


and animated like this

When I did Panzer General in Windows Phone 6/7 using WPF, it was very simple to use a a storyboard and an ObjectAnimation class like this

1 <Storyboard x:Name="ExplodeStoryboard"> 2 <ObjectAnimationUsingKeyFrames 3 Storyboard.TargetName="ExplodeTranslateTransform" 4 Storyboard.TargetProperty="X" Duration="0:0:1" Completed="ObjectAnimationUsingKeyFrames_Completed"> 5 <DiscreteObjectKeyFrame KeyTime="0:0:0" Value="0" /> 6 <DiscreteObjectKeyFrame KeyTime="0:0:.2" Value="-60" /> 7 <DiscreteObjectKeyFrame KeyTime="0:0:.4" Value="-120" /> 8 <DiscreteObjectKeyFrame KeyTime="0:0:.6" Value="-180" /> 9 <DiscreteObjectKeyFrame KeyTime="0:0:.8" Value="-240" /> 10 <DiscreteObjectKeyFrame KeyTime="0:0:1" Value="100" /> 11 </ObjectAnimationUsingKeyFrames> 12 </Storyboard>

In XF, it looks like there is only 1 timer available so I need to hook into it like this

1 module ChickenSoftware.PanzerGeneral.ExplodeDemo 2 3 open Xamarin.Forms 4 5 let addContent (layout:AbsoluteLayout) = 6 let image = new Image() 7 image.Source <- ImageSource.FromResource("explode0") 8 let x = 50.0 9 let y = 50.0 10 let height = 50.0 11 let width = 60.0 12 let rectangle = new Rectangle(x,y,width,height) 13 layout.Children.Add(image , rectangle) 14 15 let mutable index = 1 16 let callback = new System.Func<bool>(fun _ -> 17 match index with 18 | 1 -> image.Source <- ImageSource.FromResource("explode1"); index <- 2 19 | 2 -> image.Source <- ImageSource.FromResource("explode2"); index <- 3 20 | 3 -> image.Source <- ImageSource.FromResource("explode3"); index <- 4 21 | 4 -> image.Source <- ImageSource.FromResource("explode4"); index <- 5 22 | 5 -> image.Source <- ImageSource.FromResource("explode0"); index <- 99 23 | _ -> () 24 true) 25 Device.StartTimer(System.TimeSpan.FromSeconds(20.25),callback) 26 27 let populateImage = 28 let layout = new AbsoluteLayout() 29 layout.HeightRequest <- 5000.0 30 layout.WidthRequest <- 5000.0 31

The key lines is 16, where I create the callback function that gets called each time the timer triggers and then line 25 when the Device class has a method called “StartTimer”

This works


since there is no other animation in the game, I *think* this will work.  I guess I will see soon enough


Handling User Interaction Using Xamarin Forms (XF)

(Part 6 of the Panzer General Portable Project)

Now that I have a rudimentary board in place, I need to understand basic user interaction with the board. The most common gesture is the tap. When I creted the Windows Phone 6/7 version of this game using native WPF, it was very easy to work with these concepts. The Xamarin Forms (XF), not so much.

In XF, capturing a user’s tap on the screen is done via the TapGestureRecognizer class. For example, to see if a person taps on an given game hex you can write some code like this (lines 1 and 19 are the important ones below):

1 let tapRecognizer = new TapGestureRecognizer() 2 3 let getTerrainFrame (tile: Tile) (scale:float) = 4 let baseTile = getBaseTile tile 5 let baseTerrain = getBaseTerrainFromTerrain baseTile.Terrain 6 let tileId = baseTerrain.Id 7 let locatorPrefix = 8 match baseTerrain.Condition with 9 | LandCondition.Dry -> "tacmapdry" 10 | LandCondition.Frozen -> "tacmapfrozen" 11 | LandCondition.Muddy -> "tacmapmuddy" 12 let frame = new TileFrame(tile) 13 let terrainImageLocator = locatorPrefix + tileId.ToString() 14 let image = getImage terrainImageLocator 15 image.Scale <- (scale + 0.6) 16 frame.BackgroundColor <- Color.Transparent 17 frame.BorderColor <- Color.Transparent 18 frame.Content <- image 19 frame.GestureRecognizers.Add(tapRecognizer) 20 frame 21

The getTerrainFrame is called for each hex that is created for the game board

Since there can be multiple frames layered on top of the base terrain image (like units, nation flags, etc..) we need a way for those frames to not capture the tap event. Enter the InputTransparent property (line 8 below)

1 let getSingleUnitFrame (iconId:int) (scale:float) = 2 let frame = new Frame() 3 let path = "tacicons" + iconId.ToString() 4 let image = getImage path 5 image.Scale <- (scale + 0.6) 6 frame.BackgroundColor <- Color.Transparent 7 frame.BorderColor <- Color.Transparent 8 frame.InputTransparent <- true 9 frame.Content <- image 10 Some frame 11

With each hex’s base frame now wired up to this tap recognizer, I need a way to send data into the event and a way to get the data out of the event.

My first thought was to use the eventArgs – which is the way I have done it 100% of the time before this project. I was thinking code like this:

1 type TapEventArgs(tileId:int) = 2 inherit EventArgs() 3 member this.TileId = tileId 4

Where I have an custom event type that inherits from EventArgs and can can put whatever data I want into the additional properities – in this case the unique Id for the Hex/Tile

I could then create an event handler that handles the event and gets the needed data from the event args:

1 let handleTapEvent (sender:Object) (e:TapEventArgs) = 2 app.MainPage.DisplayAlert(e.TileId.ToString(), "OK") |> ignore 3 () 4

And then to wire things together, I would use an EventHandler class

1 let tapEventHandler = new EventHandler<TapEventArgs>(handleTapEvent) 2 tapRecognizer.Tapped.AddHandler(tapEventHandler :> EventHandler<EventArgs>) 3

Unfortunately, this does not work!  When doing a simple cast, I get

The type ‘EventArgs’ is not compatible with the type ‘TapEventArgs’

and if I try and force it into the event handler

1 let tapEventHandler = new EventHandler<TapEventArgs>(handleTapEvent)

I get this error

This expression was expected to have type ‘EventHandler’ but here has type ‘EventHandler<TapEventArgs>’

You can see my trail of tears on stack overflow here

So instead of spending my time fighting with the compiler, I decided to use the other event arg: object

1 let handleTapEvent (sender:Object) (e:EventArgs) = 2 let tileFrame = sender 😕> TileFrame 3 let tile = tileFrame.Tile 4 let baseTile = getBaseTile tile 5 let tileId = baseTile.Id.ToString() 6 app.MainPage.DisplayAlert("Tile Pressed", tileId, "OK") |> ignore 7 () 8

with the TileFrame inheriting from Frame like so

1 type TileFrame(tile:Tile) = 2 inherit Frame() 3 member this.Tile = tile 4

and I get what I need


Creating an Initial Game Board

(Part 5 of the Panzer General Portable Project)

The first game-like task I wanted to accomplish was to set up the base game board – like I did here seven years ago.  I fired up the F# Xamarin Forms (XF) project I was working on last post and open the app.fs file.  Following the “Full-On Monty” Elm pattern, I am not going to do any of this app in markup so there are no XAML files to deal with.

Inside the app.fs file, I first created a record type to keep track of the tiles and units for each hex (later in this series, I will create a proper domain model – for now this is a just a spike to see what it takes to render the game board – I named it ContentData).  Notice that ContentData always had a Tile, Row and Column, but it does not always have a unit on it – so I used an option type. for Unit.  I also needed a type for the Tile, the Unit, and the Equipment – starting with image then moving out to additional data to make the game work.  Enter type providers – all I needed to do was to point to the files that were already part of the solution to get the types

1 type TileContext = JsonProvider<"Data//Scenario_Tile.json"> 2 type UnitContext = JsonProvider<"Data//Scenario_Unit.json"> 3 type EquipmentContext = JsonProvider<"Data//Equipment.json"> 4 type ContentData = {TileId: int; ColumnNumber: int; RowNumber: int; UnitId: int option} 5

I then created three functions to get the data for each instance of those types

1 let getTiles (scenarioId:int) = 2 let assembly = IntrospectionExtensions.GetTypeInfo(typeof<App>).Assembly 3 let stream = assembly.GetManifestResourceStream("scenariotile"); 4 let reader = new StreamReader(stream) 5 let json = reader.ReadToEnd() 6 let scenarioTile = TileContext.Parse(json) 7 scenarioTile.Dataroot.ScenarioTile 8 |> Array.filter(fun st -> st.ScenarioId = scenarioId) 9 10 let getUnits (scenarioId: int) = 11 let assembly = IntrospectionExtensions.GetTypeInfo(typeof<App>).Assembly 12 let stream = assembly.GetManifestResourceStream("scenariounit"); 13 let reader = new StreamReader(stream) 14 let json = reader.ReadToEnd() 15 let unit = UnitContext.Parse(json) 16 unit.Dataroot.ScenarioUnit 17 |> Array.filter(fun su -> su.ScenarioId = scenarioId) 18 19 let getEquipments = 20 let assembly = IntrospectionExtensions.GetTypeInfo(typeof<App>).Assembly 21 let stream = assembly.GetManifestResourceStream("equipment"); 22 let reader = new StreamReader(stream) 23 let json = reader.ReadToEnd() 24 let equipment = EquipmentContext.Parse(json) 25 equipment.Dataroot.Equipment

You first thought is “this screams refactoring to a high order function” and I would agree.  I will do that in next iteration

In any event, I needed a way to create the actual image from the file path and then a way of hydrating the ContentData

1 let createImage path = 2 let image = new Image() 3 image.Source <- ImageSource.FromResource(path) 4 image 5 6 let createTileContentData (tile:TileContext.ScenarioTile) (units: UnitContext.ScenarioUnit seq) (equipments: EquipmentContext.Equipment seq) = 7 let scenarioUnit = 8 units 9 |> Seq.tryFind(fun u -> u.StartingScenarioTileId = tile.ScenarioTileId) 10 let unitId = 11 match scenarioUnit with 12 | Some u -> 13 let equipment = equipments |> Seq.find(fun e -> e.EquipmentId = u.EquipmentId) 14 Some equipment.Icon 15 | None -> None 16 17 {TileId = tile.TerrainId; 18 ColumnNumber = tile.ColumnNumber; 19 RowNumber = tile.RowNumber; 20 UnitId = unitId}

With this function ready to return the image, I needed a way to put it in the correct place on the board.  In XF, this is accomplished via the Rectangle type

1 let createRectangle columnIndex rowIndex scale = 2 let height = 50.0 * scale 3 let width = 60.0 * scale 4 let yOffsetPlug = 25.0 * scale 5 let xOffsetPlug = -15.0 * scale 6 let columnIndex' = float columnIndex 7 let rowIndex' = float rowIndex 8 let yOffset = 9 match columnIndex % 2 = 0 with 10 | true -> yOffsetPlug 11 | false -> yOffsetPlug + yOffsetPlug 12 let xOffset = (columnIndex' * xOffsetPlug) + xOffsetPlug 13 let x = xOffset + columnIndex' * width 14 let y = yOffset + rowIndex' * height 15 new Rectangle(x,y,width,height)

With the individual hex functions ready, I was ready to put them onto the screen.  In XF, there is a type called layout that seems what I need to position images in absolute positions

1 let createLayout numberOfTiles scale = 2 let width = 60.0 * scale 3 let height = 50.0 * scale 4 let layout = new AbsoluteLayout() 5 layout.WidthRequest <- 12.0 * width 6 let rows = numberOfTiles % 20 |> float 7 layout.HeightRequest <- rows * height 8 layout

With the layout ready, I could create a function that takes in the layout, an individual hex’s contentdata, find it in the image files, and put it on the board.  I used the Children property of the Layout type to push multiple images on the same hex – I am not sure about Z-ordering yet, so I put the unit image after the tile

1 let addTileContent (layout:AbsoluteLayout) (contentData: ContentData) (scale: float) = 2 let rectangle = createRectangle contentData.ColumnNumber contentData.RowNumber scale 3 let terrainImageLocator = "tacmapdry" + contentData.TileId.ToString() 4 layout.Children.Add(createImage terrainImageLocator, rectangle) 5 match contentData.UnitId with 6 |Some i -> 7 let unitImageLocator = "tacicons" + i.ToString() 8 layout.Children.Add(createImage unitImageLocator, rectangle) 9 |None -> ()

With the individual hex functions ready, I could iterate through the first scenario and populate its initial board.  Notice that I put the Content control inside a ScrollView type that then put into a ContentPage that is then put into the Page.  I think the common convention is right – UX is very much OO in nature

1 let populateBoard = 2 let tiles = getTiles 0 3 let units = getUnits 0 4 let equipments = getEquipments 5 let numberOfTiles = tiles |> Seq.length 6 let scale = 1.0 7 let layout = createLayout numberOfTiles scale 8 tiles 9 |> t -> createTileContentData t units equipments) 10 |> Array.iter(fun cd -> addTileContent layout cd scale) 11 let scrollView = new ScrollView() 12 scrollView.Orientation <- ScrollOrientation.Both 13 scrollView.Content <- layout 14 base.MainPage <- ContentPage(Content = scrollView) 15 16 do 17 populateBoard

So when I fired up the emulator, I got some pretty good first results

Screen Shot 2018-11-08 at 8.22.57 PM

Out of the box with Win Phone, I could pinch and spread a location and the screen images would automatically adjust and get bigger/smaller.  No such luck with XF – so I need to see how to do that.  In any event, zooming into the bottom left corner, all Panzer General fans will immediate recognize this layout. 


And it looks pretty good compared to the winphone


and the original game


Lots to do, but I am happy with the progress

Gist is here

Creating File Reference For An XF Shared .FSProj File

(Part 4 of the Panzer General Portable Project)

As I talked about in the last post, I have about 700 images to be referenced from the Panzer General Portable game.  When dealing with images in Xamarin Forms (XF), there are two choices:  make the image an embedded resource in the shared project or create a stub in the shared project and have the image in both the iOS and Android project.  Following Occam’s Razor, I opted for one file in the shared project.

Going back to the project, I opened the shared project and added the folder that contained all of the images.  A demo project looks like this:

Screen Shot 2018-11-08 at 6.15.01 PM

So far so good. 

I then high-lighted all of the images (that took a bit) and right clicked –> Build Action –> EmbeddedResource

Screen Shot 2018-11-08 at 6.16.20 PM

Visual Studio then tagged each of the files with a ResourceId of the file name:

Screen Shot 2018-11-08 at 6.15.29 PM

So far, so bad.  When I tried to reference these files in my code, the app could not find the images

So it turns out that when you are doing cross-platform development, Xamarin tries to reconcile any problems to the lowest level.  In this case, Android has some very specific opinions about naming and the file names that I used did not match.  iOS does not seem to have such limitations.   The frustrating thing for me is that Visual Studio for Mac let me assign illegal values and did not issue any warnings so it took way too long of trial and error to figure this out.  In my case, I used an underscore “_", which is an illegal character.

When I renamed a test image and followed the same steps, I got it working

Screen Shot 2018-11-08 at 6.15.48 PM

So I then went back and changed the naming of the photo parsing script.  But then I realized that highlighting all of the files in the solution explorer is a drag, so I wrote a new script that gave the correct file name and ResourceId for the fsproj file:

1 let createBlock (resource:string) (logicalName:string)= 2 ""\"><LogicalName>" + logicalName + "</LogicalName></EmbeddedResource>"

I then looped though all of the images files and created a text file

1 let getOutput path = 2 let resources = getResources path 3 let logicalNames = getLogicalNames path 4 resources 5 |> logicalNames 6 |> (r,ln) -> createBlock ln r) 7 |> s -> " " + s)

the getLogicalNames function makes the ResourceId (Logical name in the .fsproj) acceptable to Android

1 let getLogicalNames path = 2 subDirectoryInfos path 3 |> Array.collect(fun sdi -> sdi.GetFiles()) 4 |> f -> f.Name) 5 |> n -> n.ToLowerInvariant()) 6 |> n -> n.Replace(".jpeg",String.Empty)) 7 |> n -> n.Replace("_",String.Empty))

I took the contents of that file, open the Panzer General project .fsproj file, pasted it in, and I got my images working

Gist is here

Creating Mobile Apps With Xamarin.Forms and Visual Studio For Mac Using F#

I have worked through chapters one to nine in Petzold’s Creating Mobile Apps with Xamarin.Forms using Visual Studio For the Mac and F#.  I found a couple of gotchas that might trip up someone doing the same that I thought I could document here.  I am using a Mac Book Pro and Visual Studio Enterprise For Mac 2017.

1) The code samples found on GitHub are in C# with a folder for the F# port – well until chapter nine when he stopped with port.  Since we are in a “Pull Request or STFU” world, I will be adding my samples for chapter 9 and beyond.

Issue #1

When you fire up Visual Studio for Mac and Select File –> New Solution –> Single View App (iOS –> app) and follow the default prompts, you will get a skeleton of a project.  Selecting Main.storyboard bring you to a designer that you can drag and drop controls onto an iPhone application, like a Label.  A problem arises when you try and given the Label a name like “testLabel”


Just by setting the name, when you try and run your app, you get this error:

Objective-C exception thrown.  Name: NSUnknownKeyException Reason: [<ViewController 0x7f90f7a11310> setValue:forUndefinedKey:]: this class is not key value coding-compliant for the key testLabel.

The problem is that the IDE does not update the code-behind of the Main.Storyboard to reflect the new name.  If you open that file using “Source Code Editor”, you can then rename the id to “testLabel” from “name-outlet-197” and delete the destination attribute. 


The project then runs

Issue #2

When you add a new File to an existing solution, in this case “MyPage”,

Screen Shot 2018-06-20 at 6.35.11 AM


it shows up alphabetically in the solution explorer


If you try and reference that new file in the App.xaml to display it on startup, you get the following error:

Screen Shot 2018-06-20 at 6.37.17 AM

This is because in F#, the ordering of files is important.  MyPage has to be visible to the compiler before App.xaml.  The way to fix this is to open the project items file, in this case Greetings.projitems:


Screen Shot 2018-06-20 at 6.39.08 AM

and change the new file (MyPage.fs) location from the default location (the end)

Screen Shot 2018-06-20 at 6.39.34 AM

to above the app.xaml fie

Screen Shot 2018-06-20 at 6.39.58 AM


Issue #3

Chapter 9 talks about calling native code on each device and referring to those calls from the forms project.  To achieve this, you need to add an interface to the common project


and then refer to it in the common project page


and to implement this in the iOS project


I had to ask for help on Stack Overflow here.  Note that the “Dependency” attribute is in a module at the end, above the do() function.  I’ll be adding this code to the book’s repository in a bit, but at least this post will help others along.