Question

我有F＃+ Xamarin.Forms工作，实际上没有使用C＃。它工作正常，但现在我试图在我正在创建的控件上创建一个BindableProperty。它很有用，但是当我尝试使用{DynamicResource blah}在XAML中绑定它或者在样式中绑定它时，它就会崩溃。

两者都在工作：

<dashboard:ProgressRing DotOnColor="#00d4c3" DotOffColor="#120a22" />
<dashboard:ProgressRing DotOnColor="{StaticResource dotOnColor}" DotOffColor="{StaticResource dotOffColor}" />

不工作：

<dashboard:ProgressRing DotOnColor="{DynamicResource dotOnColor}" DotOffColor="{DynamicResource dotOffColor}" />

错误：

Xamarin.Forms.Xaml.XamlParseException：位置18:29。无法分配属性＆＃34; DotOnColor＆＃34;：属性不存在，或者不可分配，或者值和属性之间的类型不匹配

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>

代码背后：

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)

我认为原因是静态成员失败 - 它是一个公共静态属性，其中Xamarin.Forms需要一个公共的静态字段。

F＃官方不会执行公共静态字段，这会在这种情况下导致问题 - 请参阅此处的一些讨论： http://www.ianvoyce.com/index.php/2010/10/01/public-static-fields-gone-from-f-2-0/

Answer 1

Xamarin.Forms肯定在寻找一个领域 - 我在https://github.com/xamarin/Xamarin.Forms/blob/master/Xamarin.Forms.Xaml/ApplyPropertiesVisitor.cs找到了以下内容：

    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;
    }

猜猜我会尝试修复它来处理公共静态属性。在我这样做之后，有关如何提交的提示吗？

在F＃中的自定义控件上创建Xamarin.Forms BindableProperty

1 个答案: