【UWP】通过 MarkupExtension 实现 ValueConveter 的依赖注入 / 开普饭

最近是真的比较闲，花了点时间算是把我自己的微博库的 nuget 包的坑填上了（https://github.com/h82258652/HN.Social.Weibo 欢迎大佬来 Star）。dino 大佬也一直忽悠我弄动画，可惜我没啥艺术细胞而且 Composition API 也不太熟悉，就只能逃了（哈哈哈）。闲着无事就刷刷 Github，看到 wpf repo 的一个 issue（https://github.com/dotnet/wpf/issues/499），确实目前的 XAML 跟控制反转这块几乎都没啥结合。控件层面由于要求无参构造函数，所以目前来看难以实现了。但 ValueConverter 这玩意，想了下，好像可以耶，于是做了下实验，成功并且写下了这篇 blog。

UWP 的 MarkupExtension 是在 16299 版本引入的，所以我们的项目必须要 target 16299 或以上。

以一般 MVVM 模式为例，创建 ViewModelLocator.cs，这里 IoC 容器我就使用最常用的 Autofac 好了，引用 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>

接下来添加一些测试代码吧。

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} 岁";            }            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，把这堆玩意注册上去。

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();        }    }}

接下来就是本文关键，通过 MarkupExtension 消费这个 PersonSayHelloConveter 了。这里我就叫 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("转换器类型没有设置");            }            return ServiceLocator.Current.GetInstance(ConverterType);        }    }}

接下来修改 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>

运行起来：

改个时间再跑起来：

还行。

理论上可以修改 MarkupExtensionReturnTypeAttribute 的 ReturnType 为 typeof(object) 然后从 IoC 容器获取任意已经注册了的东西就是了。但写完 blog 发现好像满满的伪需求的样子。ε=ε=ε=┏(゜ロ゜;)┛

【UWP】通过 MarkupExtension 实现 ValueConveter 的依赖注入

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