DependencyProperty

<Window x:Class="DependencyPropertyDemo.MainWindow"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
Title="DrawShape" Height="350" Width="525">
<Grid>
<StackPanel>
<TextBox TextChanged="TextBox_TextChanged" Name="input">0</TextBox>
<Grid>
<Polygon Name="poly" Stroke="Black" Fill="Red"/>
</Grid>
</StackPanel>
</Grid>
</Window>

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
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 DependencyPropertyDemo
{
/// <summary>
/// MainWindow.xaml 的交互逻辑
/// </summary>
public partial class MainWindow : Window
{
public static readonly DependencyProperty SidesProperty;

public int Sides
{
get { return (int)GetValue(SidesProperty); }
set { SetValue(SidesProperty,value);}
}
static MainWindow()
{
FrameworkPropertyMetadata md = new FrameworkPropertyMetadata();
md.PropertyChangedCallback = OnSidesChanged;
SidesProperty = DependencyProperty.Register("Sides", typeof(int), typeof(MainWindow), md);
}
public MainWindow()
{
InitializeComponent();
}

private void TextBox_TextChanged(object sender, TextChangedEventArgs e)
{
int sideCount;
bool success = int.TryParse(input.Text, out sideCount);
if (success && sideCount > 2)
{
Sides = sideCount;
}
}
static void OnSidesChanged(DependencyObject obj, DependencyPropertyChangedEventArgs args)
{
MainWindow win = obj as MainWindow;
if (win == null || win.poly == null) return;

const int xCenter = 65;
const int yCenter = 50;
const int radius = 40;
double rds = Math.PI / win.Sides * 2;

win.poly.Points.Clear();
win.poly.Points.Add(new Point(xCenter+radius,yCenter));
for (double i = 1; i <= win.Sides - 1; i++)
{
double x = (Math.Cos(rds * i) * radius) + xCenter;
double y = (Math.Sin(rds * i) * radius) + yCenter;
win.poly.Points.Add(new Point(x, y));
}
}
}
}