Creating a Xamarin.Forms BindableProperty in a custom control in F #
I have F # + Xamarin.Forms working without using C #. It works fine, but now I am trying to create a BindableProperty for the control I am creating. It works, but when I try to bind it to XAML with {DynamicResource blah} or styled then it all falls apart.
Both workers:
<dashboard:ProgressRing DotOnColor="#00d4c3" DotOffColor="#120a22" />
<dashboard:ProgressRing DotOnColor="{StaticResource dotOnColor}" DotOffColor="{StaticResource dotOffColor}" />
Does not work:
<dashboard:ProgressRing DotOnColor="{DynamicResource dotOnColor}" DotOffColor="{DynamicResource dotOffColor}" />
Mistake:
Xamarin.Forms.Xaml.XamlParseException: Position 18:29. Cannot assign property "DotOnColor": property does not exist or cannot be assigned or does not match the 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 reason for this is the failure of the static member - it is a public static property where Xamarin.Forms expects a public static field.
F # does not officially execute public static fields, which causes problems in situations like this - see the discussion here: http://www.ianvoyce.com/index.php/2010/10/01/public-static-fields-gone-from -f-2-0 /
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Xamarin.Forms is definitely looking for a field - I found the following at 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;
}
Suppose I try to fix this to handle public static properties. After I do this, any tips on how to submit?
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