MAUI中构建跨平台原生控件实现

简介

MAUI中使用Handler体系来处理不同平台的原生控件实现, 即对应的, 如果我们想要创建控件, 只需要创建基于不同平台的Handler即可。
那么下面主要教大家如何通过创建Handler(事件处理程序)来构建自己的控件。

开始

下面, 将通过创建一个进度条控件案例, 来演示如何在MAUI项目中创建平台控件并且使用它。
假设控件包含基础的三项功能, 进度条颜色(Foreground)、进度条当前值(Value)、进度条模式(Indeterminate)
1.第一步(声明控件类)
首先, 创建MyProgressBar类, 定义对应的依赖属性

internal class MyProgressBar : View
    {
        public static readonly BindableProperty ForegroundProperty =
            BindableProperty.Create(nameof(Foreground),
                typeof(Color),
                typeof(MyProgressBar),
                Colors.Transparent);

        public static readonly BindableProperty ValueProperty =
           BindableProperty.Create(nameof(Value),
               typeof(double),
               typeof(MyProgressBar),
               0.0);

        public static readonly BindableProperty IndeterminateProperty =
           BindableProperty.Create(nameof(Indeterminate),
               typeof(bool),
               typeof(MyProgressBar),
               false);

        public Color Foreground
        {
            get { return (Color)GetValue(ForegroundProperty); }
            set { SetValue(ForegroundProperty, value); }
        }
         
        public double Value
        {
            get { return (double)GetValue(ValueProperty); }
            set { SetValue(ValueProperty, value); }
        }

        public bool Indeterminate
        {
            get { return (bool)GetValue(IndeterminateProperty); }
            set { SetValue(IndeterminateProperty, value); }
        }
    }

2.第二步(创建标准处理程序)
有了控件的标准属性定义之后, 接下来就是定义标准的Handler处理程序, 其中包含控件属性映射器及构造函数, 如下所示:

   partial class MyProgressBarHandler
    {
        public static PropertyMapper<MyProgressBar, MyProgressBarHandler> HorizontalProgressBarMapper = new
        (ViewHandler.ViewMapper)
        {
            [nameof(MyProgressBar.Value)] = MapValue,
            [nameof(MyProgressBar.Foreground)] = MapForeground, 
            [nameof(MyProgressBar.Indeterminate)]= MapIndeterminate
        };

        public MyProgressBarHandler(PropertyMapper mapper)
            : base(mapper)
        {

        }

        public MyProgressBarHandler() : base(HorizontalProgressBarMapper)
        {

        }
    }

3.第三步(创建平台处理程序)
在属性映射器中, 我们可以很轻松看见对应了三个属性的事件处理程序, 但是目前并没有定义它, 这意味着你需要在不同平台下分别实现对应的
三个事件处理程序, 所以很快阿, 赶紧在Platforms > Android > Controls 下定义了一个MyProgressBarHandler, 如下所示:

接着继承于ViewHandler并且与原生安卓ProgressBar关联。

using Android.Widget;

partial class MyProgressBarHandler :
        ViewHandler<MyProgressBar, ProgressBar>
    { 

    }

重写CreateNativeView(这是创建本地控件最开始的地方)

protected override ProgressBar CreateNativeView()
        {
            return new ProgressBar(Context, null,  Android.Resource.Attribute.ProgressBarStyleHorizontal)
            {
                Indeterminate = true,
                Max = 10000,
            }; 
        }

紧接着, 实现三个事件处理程序方法, MapValue、MapForeground、MapIndeterminate

        static void MapValue(MyProgressBarHandler handler, MyProgressBar view)
        {
            var nativeView= handler?.NativeView;
            nativeView.Progress = (int)(view.Value * Max);
        }

        static void MapForeground(MyProgressBarHandler handler, MyProgressBar view)
        {
            UpdateForeground(handler?.NativeView, view.Foreground);

            static void UpdateForeground(ProgressBar nativeProgressBar, Color color)
            {
                if (color == null)
                {
                    (nativeProgressBar.Indeterminate ? nativeProgressBar.IndeterminateDrawable :
                        nativeProgressBar.ProgressDrawable)?.ClearColorFilter();
                }
                else
                {
                    var tintList = ColorStateList.ValueOf(color.ToNative());

                    if (nativeProgressBar.Indeterminate)
                        nativeProgressBar.IndeterminateTintList = tintList;
                    else
                        nativeProgressBar.ProgressTintList = tintList;
                }
            }
        }

        static void MapIndeterminate(MyProgressBarHandler handler, MyProgressBar view)
        {
           var nativeView= handler?.NativeView;
            nativeView.Indeterminate = view.Indeterminate;
        }

4. 对应的实现iOS平台的Handler事件处理程序, 与上步骤相同, 对于事件的处理细节则对应不同平台的逻辑处理。

partial class MyProgressBarHandler :
        ViewHandler<MyProgressBar, UIProgressView>
    {
        protected override UIProgressView CreateNativeView()
        {
            return new UIProgressView(UIProgressViewStyle.Default);
        }
         
        static void MapValue(MyProgressBarHandler handler, MyProgressBar view)
        {
            var nativeView = handler.NativeView;
            nativeView.Progress = (float)view.Value;
        }

        static void MapForeground(MyProgressBarHandler handler, MyProgressBar view)
        {
            var nativeView = handler.NativeView;
            nativeView.ProgressTintColor = view.Foreground?.ToNative();
        } 

        static void MapIndeterminate(MyProgressBarHandler handler, MyProgressBar view)
        {
            //...
        }
    } 

5.打开MauiProgram文件, 添加AddHandler

public static MauiApp CreateMauiApp()
        {
            var builder = MauiApp.CreateBuilder();
            builder.UseMauiApp<App>()
                .ConfigureFonts(fonts =>
                {
                    fonts.AddFont("OpenSans-Regular.ttf", "OpenSansRegular");
                })
                .ConfigureMauiHandlers(handler =>
                {
                  handler.AddHandler(typeof(MyProgressBar), typeof(MyProgressBarHandler));
                });  
            return builder.Build();
        }

6.界面中,分别声明MAUI原生控件与自定义控件

<ContentPage xmlns="http://schemas.microsoft.com/dotnet/2021/maui"
             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
             x:Class="MAUIRender.MainPage"
             xmlns:my="clr-namespace:MAUIRender" 
             xmlns:ctor="clr-namespace:MAUIRender.Controls" 
             BackgroundColor="{DynamicResource SecondaryColor}">
    <Grid>
        <StackLayout>
            <ProgressBar   
                Progress="30" ProgressColor="Red"/>
            
            <ctor:MyProgressBar 
                Indeterminate="True"
                Value="600"  Foreground="Green" />
        </StackLayout>
    </Grid>
</ContentPage>

运行实际效果:

总结

通过利用Handler来处理不同平台控件的行为, 与控件本身解耦并且更加容器支持更多的平台。