Xamarin.iOS中ArcSegment无法动态更新问题求助

问题场景 #

在Xamarin.iOS中使用ArcSegment时，首次加载正常，但动态修改Point属性后界面无变化（控制台显示值已更改）；UWP端同样存在该问题，同时Xamarin.iOS热重载提示找不到Xamarin.HotReload.Translations.resources程序集。

XAML代码 #

<Path x:Name="PathCircle" Stroke="Black" StrokeThickness="17" StrokeLineJoin="Round" TranslationX="125" TranslationY="530">
    <Path.Data >
        <PathGeometry>
            <PathFigure StartPoint="0, 0" >
                <ArcSegment  x:Name="CircleClim" Size="80, 80"
                Point="32, -64" 
                IsLargeArc="False" 
                SweepDirection="Clockwise" />
            </PathFigure>
        </PathGeometry>
    </Path.Data>
</Path>

后台更新代码 #

private void SwitchCircleClim()
{
    double radius = 80;
    double angle = (10-temp)*9*Math.PI/180;

    double x = 80 +(radius * Math.Cos(angle));
    double y = (radius * Math.Sin(angle));
    CircleClim.Point=new Point(x, y);   
    Console.WriteLine(CircleClim.Point.X);
    Console.WriteLine(CircleClim.Point.Y);
}

解决方法 #

1. 强制刷新Path的Data属性 #

ArcSegment属于PathGeometry的子元素，修改其属性后不会自动触发UI更新，需手动重置Path.Data通知界面刷新：

private void SwitchCircleClim()
{
    double radius = 80;
    double angle = (10-temp)*9*Math.PI/180;

    double x = 80 +(radius * Math.Cos(angle));
    double y = (radius * Math.Sin(angle));
    CircleClim.Point=new Point(x, y);   

    // 强制刷新Data属性
    var tempData = PathCircle.Data;
    PathCircle.Data = null;
    PathCircle.Data = tempData;
}

或者直接重新构建PathGeometry，彻底触发更新：

private void SwitchCircleClim()
{
    double radius = 80;
    double angle = (10-temp)*9*Math.PI/180;

    double x = 80 +(radius * Math.Cos(angle));
    double y = (radius * Math.Sin(angle));

    var pathGeometry = new PathGeometry();
    var pathFigure = new PathFigure { StartPoint = new Point(0, 0) };
    var arcSegment = new ArcSegment
    {
        Size = new Size(80, 80),
        Point = new Point(x, y),
        IsLargeArc = false,
        SweepDirection = SweepDirection.Clockwise
    };
    pathFigure.Segments.Add(arcSegment);
    pathGeometry.Figures.Add(pathFigure);

    PathCircle.Data = pathGeometry;
}

2. 使用数据绑定替代直接修改属性 #

通过MVVM绑定ArcSegment.Point到ViewModel的可绑定属性，利用数据绑定自动更新机制：

ViewModel定义可绑定属性

private Point _arcPoint;
public Point ArcPoint
{
    get => _arcPoint;
    set
    {
        _arcPoint = value;
        OnPropertyChanged();
    }
}

public event PropertyChangedEventHandler PropertyChanged;
protected void OnPropertyChanged([CallerMemberName] string propertyName = null)
{
    PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
}

XAML绑定Point属性

<ArcSegment  x:Name="CircleClim" Size="80, 80"
             Point="{Binding ArcPoint}" 
             IsLargeArc="False" 
             SweepDirection="Clockwise" />

更新ViewModel属性

private void SwitchCircleClim()
{
    double radius = 80;
    double angle = (10-temp)*9*Math.PI/180;

    double x = 80 +(radius * Math.Cos(angle));
    double y = (radius * Math.Sin(angle));
    ArcPoint = new Point(x, y);
}

3. 修复Xamarin.iOS热重载问题 #

针对热重载程序集缺失提示，执行以下操作：

• 卸载并重新安装Xamarin.HotReload NuGet包
• 清理解决方案，删除bin/obj文件夹后重新生成项目
• 确认iOS项目目标框架版本与HotReload包兼容

4. UWP端额外处理 #

UWP中修改ArcSegment属性后，可调用强制重绘方法确保界面更新：

CircleClim.Point=new Point(x, y);
PathCircle.InvalidateArrange();
PathCircle.UpdateLayout();

内容的提问来源于stack exchange，提问作者Antoine21000