Question

SOLUTION
Dynamic Margin on Window Drag

So I’m trying to get my polygon to move as the window is moved. I have;

    private void ResetPolygon(Point Point1, Point Point2, Point Point3)
    {
        SpeechPoly.Points.Clear();
        ObservableCollection<Point> myPointCollection = new ObservableCollection<Point>();
        myPointCollection.Add(Point3);
        myPointCollection.Add(Point2);
        myPointCollection.Add(Point1);
        foreach (Point p in myPointCollection)
        {
            SpeechPoly.Points.Add(p);
        }
    }

    private void Window_LocationChanged(object sender, EventArgs e)
    {
        if (this.IsLoaded)
        {
            Point Point1 = new Point(newPoint3);
            Point Point2 = new Point(newPoint2);
            Point Point3 = new Point(newPoint1);
            ResetPolygon(newPoint1, newPoint2, newPoint3);

//Write out the values of both the list and the polygon to screen!
            txtBlock.Text = newPoint1.X.ToString("N2") + ", " + newPoint1.Y.ToString("N2") + 
"\n" + newPoint2.X.ToString("N2") + ", " + newPoint2.Y.ToString("N2") + "\n" + 
newPoint3.X.ToString("N2") + ", " + newPoint3.Y.ToString("N2");

            txtBlock.Text += "\n" + SpeechPoly.Points[0].X.ToString("N2") + ", " + 
SpeechPoly.Points[0].Y.ToString("N2") + "\n" + SpeechPoly.Points[1].X.ToString("N2") + ", " +        
SpeechPoly.Points[1].Y.ToString("N2") + "\n" + SpeechPoly.Points[2].X.ToString("N2") + ", "+ 
SpeechPoly.Points[2].Y.ToString("N2");
                        }
                    }

But the Polygon remains the same shape no matter what, even though the Textblock clearly shows the values of all the Points in the List and the Polygon‘s points are definitely changing.

I’ve also tried to bind the Points property of the Polygon to my code.

<Polygon
    Name="SpeechPoly"
    Points="{Binding myPointCollection, RelativeSource={RelativeSource FindAncestor, AncestorType=Window}}"
    Stroke="Black" 
    StrokeThickness="2"
    </Polygon>

I’ve also tried using a pointsCollection as opposed List<Points> but same result. Almost seems like the Polygon is not refreshing.

Answer 1

I was not being satisfied with the previous answer I gave as it is after all a workaround..

I found a better solution to the problem which will not require to reset the databinds.

So the binding from XAML is being directed to a property with INCC however the data itself is converted to Points for the polygon to use when drawing.

<Window x:Class="WpfApplication9.MainWindow"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:local="clr-namespace:WpfApplication9"
    Title="MainWindow" Height="350" Width="525" LocationChanged="Window_LocationChanged" >
<Window.Resources>
    <local:MyPointCollectionConverter x:Key="mcolconv" />
</Window.Resources>
<Canvas>
    <Polygon Name="SpeechPoly" Stroke="Black" StrokeThickness="2" 
             Points="{Binding Path=myPointCollection, Converter={StaticResource mcolconv}}" />
</Canvas>

using System;
using System.Collections.ObjectModel;
using System.ComponentModel;
using System.Windows;
using System.Windows.Data;
using System.Windows.Media;

namespace WpfApplication9
{
/// <summary>
/// Interaction logic for MainWindow.xaml
/// </summary>
public partial class MainWindow : Window, INotifyPropertyChanged
{
    public event PropertyChangedEventHandler PropertyChanged;

    private ObservableCollection<Point> _myPointCollection = new ObservableCollection<Point>();
    public ObservableCollection<Point> myPointCollection { get { return _myPointCollection; } }

    public MainWindow()
    {
        myPointCollection.Add(new Point(100, 50));
        myPointCollection.Add(new Point(150, 100));
        myPointCollection.Add(new Point(50, 100));
        InitializeComponent();
        DataContext = this;
    }

    private void ResetPolygon(Point Point1, Point Point2, Point Point3)
    {
        myPointCollection.Clear();
        myPointCollection.Add(Point1);
        myPointCollection.Add(Point2);
        myPointCollection.Add(Point3);
        if (PropertyChanged != null)
            PropertyChanged(this, new PropertyChangedEventArgs("myPointCollection"));
    }

    private void Window_LocationChanged(object sender, EventArgs e)
    {
        if (this.IsLoaded)
        {
            Random rnd = new Random();
            Point Point1 = new Point(rnd.Next(50, 200), rnd.Next(50, 200));
            Point Point2 = new Point(rnd.Next(50, 200), rnd.Next(50, 200));
            Point Point3 = new Point(rnd.Next(50, 200), rnd.Next(50, 200));
            ResetPolygon(Point1, Point2, Point3);
        }

    }
}

public class MyPointCollectionConverter : IValueConverter
{
    #region IValueConverter Members

    public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
    {
        var regPtsColl = new PointCollection(); //regular points collection.
        var obsPtsColl = (ObservableCollection<Point>)value; //observable which is used to raise INCC event.
        foreach (var point in obsPtsColl)
            regPtsColl.Add(point);
        return regPtsColl;
    }

    public object ConvertBack(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
    {
        return null;
    }

    #endregion
}
}