Csharp .NET Maui 自定义 SkiaSharp 控件可绑定属性未按预期运行

我的头衔很烂，你可以随意改.

我找到一张tutorial for making custom controls in Maui using SkiaSharp美元的钞票.我使用C#标记而不是XAML对其进行了一些修改.除了必须用ProgressBar.Maui.ProgressBar progressBar而不是ProgressBar progressBar实例化进度条之外，一切都运行得很好.

我想稍微修改一下，将重画限制为仅在达到某个进度更改阈值后才会发生.(即，每x%进度只重画一次).我添加了一个按小于阈值的速度递增进度的按钮，因此我应该必须单击这些按钮几次才能看到进度条更新.但是，每次我单击该按钮时，进度条都会更新.

如果我手动更改进度，比如将progressBar.Progress = 0.01f;添加到页面构造函数的末尾，进度栏将按预期运行.

以下是所有相关代码[我认为]

我的库项目只有2个文件

ProgressBar.cs个

using SkiaSharp;
using SkiaSharp.Views.Maui;
using SkiaSharp.Views.Maui.Controls;
using System.Diagnostics;

namespace ProgressBar.Maui;

// All the code in this file is included in all platforms.
public class ProgressBar : SKCanvasView
{
   public static readonly BindableProperty ProgressProperty =
   BindableProperty.Create(nameof(Progress), typeof(float), typeof(ProgressBar), 0f, propertyChanged: OnBindablePropertyChanged);

   public static readonly BindableProperty ProgressColorProperty =
      BindableProperty.Create(nameof(ProgressColor), typeof(Color), typeof(ProgressBar), Colors.CornflowerBlue, propertyChanged: OnBindablePropertyChanged);

   public static readonly BindableProperty BaseColorProperty =
      BindableProperty.Create(nameof(BaseColor), typeof(Color), typeof(ProgressBar), Colors.LightGray, propertyChanged: OnBindablePropertyChanged);

   public float Progress
   {
      get => (float)GetValue(ProgressProperty);
      set
      {
         if (Math.Abs(value - _previousProgress) >= _RedrawThreshold)
         {
            SetValue(ProgressProperty, value);
            _previousProgress = value;
            Debug.WriteLine("Progress updated 和 surface invalidated.");
         }
         else
         {
            Debug.WriteLine("Progress change below threshold. No redraw.");
         }
      }
   }

   public Color ProgressColor
   {
      get => (Color)GetValue(ProgressColorProperty);
      set => SetValue(ProgressColorProperty, value);
   }
   public Color BaseColor
   {
      get => (Color)GetValue(BaseColorProperty);
      set => SetValue(BaseColorProperty, value);
   }


   // actual canvas instance to draw on
   private SKCanvas _canvas;

   // rectangle which will be used to draw the Progress Bar
   private SKRect _drawRect;

   // holds information about the dimensions, etc.
   private SKImageInfo _info;

   private const float _RedrawThreshold = 0.5f; // 1% change
   private float _previousProgress = 0f;

   private SKPaint _basePaint = new()
   {
      Style = SKPaintStyle.Fill,
      IsAntialias = true,
   };

   private SKPaint _progressPaint = new()
   {
      Style = SKPaintStyle.Fill,
      IsAntialias = true,
   };



   protected override void OnPaintSurface (SKPaintSurfaceEventArgs e)
   {
      base.OnPaintSurface(e);

      _canvas = e.Surface.Canvas;
      _canvas.Clear();

      _info = e.Info;

      _drawRect = new SKRect(0, 0, _info.Width, _info.Height);

      DrawBase();
      DrawProgress();
   }

   private void DrawBase ()
   {
      using SKPath basePath = new();

      basePath.AddRect(_drawRect);

      _basePaint.Color = BaseColor.ToSKColor();

      _canvas.DrawPath(basePath, _basePaint);
   }

   private void DrawProgress ()
   {
      using SKPath progressPath = new();

      var progressRect = new SKRect(0, 0, _info.Width * Progress, _info.Height);

      progressPath.AddRect(progressRect);

      _progressPaint.Color = ProgressColor.ToSKColor();

      _canvas.DrawPath(progressPath, _progressPaint);
   }

   private static void OnBindablePropertyChanged (BindableObject bindable, object oldValue, object newValue)
   {
      if (oldValue != newValue)
         ((ProgressBar)bindable).InvalidateSurface();
   }
}

和

Registration.cs个

using SkiaSharp.Views.Maui.H和lers;

namespace ProgressBar.Maui;
public static class Registration
{
   public static MauiAppBuilder UseProgressBar(this MauiAppBuilder builder)
   {
      builder.ConfigureMauiH和lers(h =>
      {
         h.AddH和ler<ProgressBar, SKCanvasViewH和ler>();
      });

      return builder;
   }
}

我的样例项目包含

SamplePage.cs个

namespace ProgressBarSample.Views;

public partial class SamplePage : ContentPage
{
   public SamplePage (SampleViewModel viewModel)
   {
      BindingContext = viewModel;

      Content = new VerticalStackLayout
      {
         Spacing = 30,
         Padding = new Thickness(30, 0),
         VerticalOptions = LayoutOptions.Center,

         Children =
         {
            new ProgressBar.Maui.ProgressBar()
            {
               WidthRequest = 300,
               HeightRequest = 5,
               ProgressColor = Colors.DeepSkyBlue,
            }
            .Assign(out ProgressBar.Maui.ProgressBar progressBar)
            .Bind(ProgressBar.Maui.ProgressBar.ProgressProperty, nameof(SampleViewModel.Progress), BindingMode.OneWay),

            new Button
            {
               Text = "Increment",
            }
            .BindComm和(nameof(SampleViewModel.IncrementProgressComm和))
         }
      };
   }
}

和

SampleViewModel.cs个

namespace ProgressBarSample.ViewModels;

public partial class SampleViewModel : BaseViewModel
{
    [ObservableProperty]
    private float progress = 0.01f;

    [RelayComm和]
    private void IncrementProgress()
    {
        Debug.WriteLine("IncrementProgress()");
        Progress +=0.01f;
    }
}

BaseViewModel.cs是继承ObservableObject的空类

我还把builder.UseProgressBar()加到了MauiProgram.cs