I have F# + Xamarin.Forms working, with no C# actually in use. It's working fine, but now I'm trying to create a BindableProperty on a Control that I'm creating. It kindof works, but when I try to bind to it in XAML with a {DynamicResource blah} or in a Style with then it all falls apart.
Both working:
<dashboard:ProgressRing DotOnColor="#00d4c3" DotOffColor="#120a22" />
<dashboard:ProgressRing DotOnColor="{StaticResource dotOnColor}" DotOffColor="{StaticResource dotOffColor}" />
Not working:
<dashboard:ProgressRing DotOnColor="{DynamicResource dotOnColor}" DotOffColor="{DynamicResource dotOffColor}" />
Error:
Xamarin.Forms.Xaml.XamlParseException: Position 18:29. Cannot assign property "DotOnColor": Property does not exists, or is not assignable, or mismatching type between value and property
XAML:
<?xml version="1.0" encoding="UTF-8"?>
<ContentView
xmlns="http://xamarin.com/schemas/2014/forms"
xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
x:Class="Dashboard.ProgressRing"
x:Name="view">
<AbsoluteLayout x:Name="absLayout">
<!-- Dots are controlled in the code behind -->
</AbsoluteLayout>
</ContentView>
Code behind:
namespace Dashboard
open System
open Xamarin.Forms
open Xamarin.Forms.Xaml
type ProgressRing() =
inherit ContentView()
do base.LoadFromXaml(typeof<ProgressRing>) |> ignore
let absLayout = base.FindByName<AbsoluteLayout>("absLayout")
static let dotOffColorProperty = BindableProperty.Create("DotOffColor", typeof<Color>, typeof<ProgressRing>, Color.Default)
static let dotOnColorProperty = BindableProperty.Create("DotOnColor", typeof<Color>, typeof<ProgressRing>, Color.Accent)
static member DotOffColorProperty = dotOffColorProperty
static member DotOnColorProperty = dotOnColorProperty
member this.DotOffColor
with get () = this.GetValue dotOffColorProperty :?> Color
and set (value:Color) =
this.SetValue(dotOffColorProperty, value)
member this.DotOnColor
with get () = this.GetValue dotOnColorProperty :?> Color
and set (value:Color) =
this.SetValue(dotOnColorProperty, value)
I believe the cause of this is the static member failing - it's a public static property, where Xamarin.Forms expects a public static field.
F# officially does not do public static fields, which causes problems in situations like this - see some discussion here: http://www.ianvoyce.com/index.php/2010/10/01/public-static-fields-gone-from-f-2-0/
Xamarin.Forms is definitely looking for a field - I found the following in https://github.com/xamarin/Xamarin.Forms/blob/master/Xamarin.Forms.Xaml/ApplyPropertiesVisitor.cs:
static BindableProperty GetBindableProperty(Type elementType, string localName, IXmlLineInfo lineInfo,
bool throwOnError = false)
{
var bindableFieldInfo =
elementType.GetFields().FirstOrDefault(fi => fi.Name == localName + "Property" && fi.IsStatic && fi.IsPublic);
Exception exception = null;
if (exception == null && bindableFieldInfo == null) {
exception =
new XamlParseException(
string.Format("BindableProperty {0} not found on {1}", localName + "Property", elementType.Name), lineInfo);
}
if (exception == null)
return bindableFieldInfo.GetValue(null) as BindableProperty;
if (throwOnError)
throw exception;
return null;
}
Guess I'll try to fix it to handle public static Properties too. After I do that, any tips on how to submit?
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