【UWP】通過 MarkupExtension 實作 ValueConveter 的依賴注入

最近是真的比較閑，花了點時間算是把我自己的微博庫的 nuget 包的坑填上了（https://github.com/h82258652/HN.Social.Weibo 歡迎大佬來 Star），dino 大佬也一直忽悠我弄影片，可惜我沒啥藝術細胞而且 Composition API 也不太熟悉，就只能逃了（哈哈哈 ），閑著無事就刷刷 Github，看到 wpf repo 的一個 issue（https://github.com/dotnet/wpf/issues/499），確實目前的 XAML 跟控制反轉這塊幾乎都沒啥結合，控制元件層面由于要求無參建構式，所以目前來看難以實作了，但 ValueConverter 這玩意，想了下，好像可以耶，于是做了下實驗，成功并且寫下了這篇 blog，

UWP 的 MarkupExtension 是在 16299 版本引入的，所以我們的專案必須要 target 16299 或以上，

以一般 MVVM 模式為例，創建 ViewModelLocator.cs，這里 IoC 容器我就使用最常用的 Autofac 好了，參考 Autofac.Extras.CommonServiceLocator 包，

public class ViewModelLocator
{
    static ViewModelLocator()
    {
        var autofacServiceLocator = new AutofacServiceLocator(CreateAutofacContainer());
        ServiceLocator.SetLocatorProvider(() => autofacServiceLocator);
    }

    private static IContainer CreateAutofacContainer()
    {
        var containerBuilder = new ContainerBuilder();

        // TODO Register services

        return containerBuilder.Build();
    }
}

并修改 App.xaml

<Application x:Class="ConverterIocDemo.App"
             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
             xmlns:viewModels="using:ConverterIocDemo.ViewModels">
    <Application.Resources>
        <ResourceDictionary>
            <viewModels:ViewModelLocator x:Key="Locator" />
        </ResourceDictionary>
    </Application.Resources>
</Application>

接下來添加一些測驗代碼吧，

namespace ConverterIocDemo.Models
{
    public class Person
    {
        public string Name { get; set; }

        public int Age { get; set; }
    }
}

using ConverterIocDemo.Models;

namespace ConverterIocDemo.Services
{
    public interface IPersonService
    {
        string GetHello(Person person);
    }
}

using System;
using ConverterIocDemo.Models;

namespace ConverterIocDemo.Services
{
    public class PersonService : IPersonService
    {
        public string GetHello(Person person)
        {
            if (person == null)
            {
                throw new ArgumentNullException(nameof(person));
            }

            var now = DateTime.Now;
            if (now.Hour >= 9 && now.Hour <= 21 && now.DayOfWeek != DayOfWeek.Sunday)
            {
                return $"大家好，我叫 {person.Name}，今年 {person.Age} 歲";
            }
            else
            {
                return "996 大法好（mmp）";
            }
        }
    }
}

using ConverterIocDemo.Models;

namespace ConverterIocDemo.ViewModels
{
    public class MainViewModel
    {
        public MainViewModel()
        {
            Person = new Person
            {
                Name = "justin liu",
                Age = 18
            };
        }

        public Person Person { get; }
    }
}

using ConverterIocDemo.Services;
using System;
using Windows.UI.Xaml.Data;
using ConverterIocDemo.Models;

namespace ConverterIocDemo.Converters
{
    public class PersonSayHelloConverter : IValueConverter
    {
        private readonly IPersonService _personService;

        public PersonSayHelloConverter(IPersonService personService)
        {
            _personService = personService;
        }

        public object Convert(object value, Type targetType, object parameter, string language)
        {
            return _personService.GetHello((Person)value);
        }

        public object ConvertBack(object value, Type targetType, object parameter, string language)
        {
            throw new NotImplementedException();
        }
    }
}

修改一下 ViewModelLocator，把這堆玩意注冊上去，

using Autofac;
using Autofac.Extras.CommonServiceLocator;
using CommonServiceLocator;
using ConverterIocDemo.Converters;
using ConverterIocDemo.Services;

namespace ConverterIocDemo.ViewModels
{
    public class ViewModelLocator
    {
        static ViewModelLocator()
        {
            var autofacServiceLocator = new AutofacServiceLocator(CreateAutofacContainer());
            ServiceLocator.SetLocatorProvider(() => autofacServiceLocator);
        }

        public MainViewModel Main => ServiceLocator.Current.GetInstance<MainViewModel>();

        private static IContainer CreateAutofacContainer()
        {
            var containerBuilder = new ContainerBuilder();

            containerBuilder.RegisterType<PersonService>().As<IPersonService>();
            containerBuilder.RegisterType<MainViewModel>();
            containerBuilder.RegisterType<PersonSayHelloConverter>().SingleInstance();

            return containerBuilder.Build();
        }
    }
}

接下來就是本文關鍵，通過 MarkupExtension 消費這個 PersonSayHelloConveter 了，這里我就叫 ConverterProviderExtension，

using CommonServiceLocator;
using System;
using Windows.UI.Xaml.Data;
using Windows.UI.Xaml.Markup;

namespace ConverterIocDemo.Converters
{
    [MarkupExtensionReturnType(ReturnType = typeof(IValueConverter))]
    public class ConverterProviderExtension : MarkupExtension
    {
        public Type ConverterType { get; set; }

        protected override object ProvideValue()
        {
            if (ConverterType == null)
            {
                throw new ArgumentException("轉換器型別沒有設定");
            }

            return ServiceLocator.Current.GetInstance(ConverterType);
        }
    }
}

接下來修改 MainPage 看看效果了

<Page x:Class="ConverterIocDemo.MainPage"
      xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
      xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
      xmlns:converters="using:ConverterIocDemo.Converters"
      xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
      xmlns:local="using:ConverterIocDemo"
      xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
      Background="{ThemeResource ApplicationPageBackgroundThemeBrush}"
      DataContext="{Binding Source={StaticResource Locator}, Path=Main}"
      mc:Ignorable="d">
    <Grid>
        <TextBlock HorizontalAlignment="Center"
                   VerticalAlignment="Center"
                   Text="{Binding Path=Person, Converter={converters:ConverterProvider ConverterType=converters:PersonSayHelloConverter}}" />
    </Grid>
</Page>

運行起來：

改個時間再跑起來：

還行，

理論上可以修改 MarkupExtensionReturnTypeAttribute 的 ReturnType 為 typeof(object) 然后從 IoC 容器獲取任意已經注冊了的東西就是了，但寫完 blog 發現好像滿滿的偽需求的樣子，ε=ε=ε=┏(゜ロ゜;)┛

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