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;elsenativeProgressBar.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。