Xamarin iOS -使用PlatformEffect设置按钮按下时的颜色

using Xamarin.Forms.Platform.iOS;
using UIKit;

[assembly: ResolutionGroupName("CustomEffects")]
[assembly: ExportEffect(typeof(CustomEffects.iOS.ButtonPressEffect), "ButtonPressEffect")]

namespace CustomEffects.iOS
{
    public class ButtonPressEffect : PlatformEffect
    {
        protected override void OnAttached()
        {
            var control = Control as UIButton;
            if (control != null)
            {
                control.TouchDown += OnButtonPressed;
                control.TouchUpInside += OnButtonReleased;
            }
        }

        protected override void OnDetached()
        {
            var control = Control as UIButton;
            if (control != null)
            {
                control.TouchDown -= OnButtonPressed;
                control.TouchUpInside -= OnButtonReleased;
            }
        }

        private void OnButtonPressed(object sender, EventArgs e)
        {
            // 设置按钮按下时的颜色效果
            var control = (UIButton)sender;
            control.BackgroundColor = UIColor.Blue;
        }

        private void OnButtonReleased(object sender, EventArgs e)
        {
            // 恢复按钮原来的颜色
            var control = (UIButton)sender;
            control.BackgroundColor = UIColor.Clear;
        }
    }
}

<Button Text="Press Me">
    <Button.Effects>
        <effect:ButtonPressEffect />
    </Button.Effects>
</Button>

using Xamarin.Forms;
using Xamarin.Forms.Platform.iOS;

namespace CustomEffects.iOS
{
    [Register("AppDelegate")]
    public partial class AppDelegate : FormsApplicationDelegate
    {
        public override bool FinishedLaunching(UIApplication app, NSDictionary options)
        {
            Forms.Init();
            LoadApplication(new App());

            // 注册自定义效果
            Xamarin.Forms.Forms.SetFlags("CollectionView_Experimental");
            Xamarin.Forms.Forms.Init();
            PlatformEffect.Init();

            return base.FinishedLaunching(app, options);
        }
    }
}