WPF---依赖属性（二）

一、概要

我们将会通过一个简单的综合例子来阐述下依赖属性的变化。

场景：我们在一个文本框中输入一个数字，然后对应的panel中会出现对应的椭圆，椭圆的个数与输入的文本相同。

我们在MainWindow中定义一个名字叫CountProperty的依赖属性，该属性关联到一个回调方法OnCountChanged，当依赖属性发生变化的时候，会触发该方法。

在文本框的事件处理程序来动态修改依赖属性的值，使回调方法OnCountChanged触发，然后在这个函数中画出椭圆。

参考代码如下：

 1 using System.Windows;
 2 using System.Windows.Controls;
 3 using System.Windows.Media;
 4 using System.Windows.Shapes;
 5
 6 namespace DependencyDemo
 7 {
 8     /// <summary>
 9     /// Interaction logic for MainWindow.xaml
10     /// </summary>
11     public partial class MainWindow : Window
12     {
13         public MainWindow()
14         {
15             InitializeComponent();
16         }
17         public int Count
18         {
19             get { return (int)GetValue(CountProperty); }
20             set { SetValue(CountProperty, value); }
21         }
22
23         // Using a DependencyProperty as the backing store for Count.  This enables animation, styling, binding, etc...
24         public static readonly DependencyProperty CountProperty =
25             DependencyProperty.Register("Count", typeof(int), typeof(MainWindow), new FrameworkPropertyMetadata(new PropertyChangedCallback(OnCountChanged)));
26
27        public static void OnCountChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
28         {
29             MainWindow win = d as MainWindow;
30             win.wrapPanel?.Children.Clear();
31             int myCount = (int)e.NewValue;
32             for (int i = 0; i < myCount; i++)
33             {
34                 win.wrapPanel?.Children.Add(new Ellipse() { Height = 20, Width = 20, Stroke = Brushes.Red, Margin = new Thickness(1) });
35             }
36         }
37
38         private void TextBox_TextChanged(object sender, TextChangedEventArgs e)
39         {
40             int myCount = 0;
41             bool isSuccess = int.TryParse(this.tbInput.Text, out myCount);
42             if(isSuccess && myCount > 0)
43             {
44                 Count = myCount;
45             }
46         }
47     }
48 }

 1 <Window x:Class="DependencyDemo.MainWindow"
 2         xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
 3         xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
 4         xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
 5         xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
 6         xmlns:local="clr-namespace:DependencyDemo"
 7         mc:Ignorable="d"
 8         Title="MainWindow" Height="350" Width="315">
 9     <Grid>
10         <Grid.RowDefinitions>
11             <RowDefinition Height="21*"/>
12             <RowDefinition Height="139*"/>
13         </Grid.RowDefinitions>
14         <StackPanel Orientation="Horizontal">
15             <Label Content="椭圆个数：" FontSize="16"></Label>
16             <TextBox Width="200" Margin="5" TextChanged="TextBox_TextChanged" Name="tbInput"></TextBox>
17         </StackPanel>
18         <ScrollViewer  Grid.Row="1">
19             <WrapPanel Name="wrapPanel" >
20             </WrapPanel>
21         </ScrollViewer>
22     </Grid>
23 </Window>

运行结果如下：