wpf 通过附加属性实现绑定显示直线图

1 新建wpf应用

2 新建MainViewModel类

using System;
using System.Collections.Generic;
using System.Collections.ObjectModel;
using System.ComponentModel;
using System.Text;
using System.Threading.Tasks;
using System.Windows;

namespace WpfApp5
{
    public class MainViewModel:INotifyPropertyChanged
    {
        public ObservableCollection Points { get; set; } = new ObservableCollection();

        private int _OffsetX = 0;

        public int OffsetX
        {
            get { return _OffsetX; }
            set { _OffsetX = value; PropertyChanged?.Invoke(this, new PropertyChangedEventArgs("OffsetX")); }
        }


        public MainViewModel()
        {
            Task.Run(async () =>
            {
                double angle = 0.0;
                double x = 0.0;
                while (angle < 360)
                {
                    await Task.Delay(50);

                    double value = Math.Cos(Math.PI * (angle / 180));
                    angle += 30;
                    Application.Current.Dispatcher.Invoke(() =>
                    {
                        Points.Add(new Point(x, value * 40 + 50));
                        x += 20;
                       
                        if (Points.Count > 50)
                        {
                            OffsetX -=20;                            
                            Points.RemoveAt(0);
                        }
                    });



                    if (angle >= 360)
                    {
                        angle = 0.0;
                    }
                        
                }
            });
        }

        public event PropertyChangedEventHandler PropertyChanged;
    }
}

3 在MainWindow.xaml上添加PolyLine，因为其Points属性是PointCollection类型，该类型没有实现INotifyCollectionChanged, INotifyPropertyChanged这些接口，所以考虑添加附件属性来作为中转来绑定

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Imaging;
using System.Windows.Navigation;
using System.Windows.Shapes;

namespace WpfApp5
{
    /// 

    /// Interaction logic for MainWindow.xaml
    /// 
    public partial class MainWindow : Window
    {
        public MainWindow()
        {
            InitializeComponent();
            this.DataContext = new MainViewModel();
        }
    }
}

 4 新建PointsHelper类，添加附件属性PointsProperty，在其PropertyChangedCallback关联的委托中为PolyLine的Points属性来赋值。

using System;
using System.Collections.Generic;
using System.Collections.ObjectModel;
using System.Text;
using System.Windows;
using System.Windows.Shapes;

namespace WpfApp5
{
    public class PointsHelper
    {


        public static ObservableCollection GetPoints(DependencyObject obj)
        {
            return (ObservableCollection)obj.GetValue(PointsProperty);
        }

        public static void SetPoints(DependencyObject obj, int value)
        {
            obj.SetValue(PointsProperty, value);
        }

        // Using a DependencyProperty as the backing store for MyProperty.  This enables animation, styling, binding, etc...
        public static readonly DependencyProperty PointsProperty =
            DependencyProperty.RegisterAttached("Points", typeof(ObservableCollection), typeof(PointsHelper), new PropertyMetadata(null, new PropertyChangedCallback(OnPointsChanged)));

        private static void OnPointsChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
        {
            var obj = d as Polyline;
            var ps = e.NewValue as ObservableCollection;
            ps.CollectionChanged += (se, ev) =>
            {
                obj.Points = new System.Windows.Media.PointCollection(e.NewValue as ObservableCollection);
            };
        }

        
    }
}