示例：
此示例直观地显示了 Windows Presentation Foundation （WPF） 中四个与宽度相关的属性之间的呈现行为差异。
FrameworkElement 类公开四个描述元素宽度特征的属性。 这四个属性可能会发生冲突，当它们发生冲突时，优先值将按如下方式确定：MinWidth 值优先于 MaxWidth 值，而值又优先于 Width 值。 第四个属性 ActualWidth是只读的，它报告通过与布局过程的交互所确定的实际宽度。
以下可扩展应用程序标记语言（XAML）示例将 Rectangle 元素（rect1）绘制为 Canvas子级。 可以使用表示 Rectangle、ListBox和 MinWidth属性值的一系列 MaxWidth 元素来更改 Width 的宽度属性。 通过这种方式，每个属性的优先级会以可视化形式显示。
<Canvas Height="200" MinWidth="200" Background="#b0c4de" VerticalAlignment="Top" HorizontalAlignment="Center" Name="myCanvas">
<Rectangle HorizontalAlignment="Center" Canvas.Top="50" Canvas.Left="50" Name="rect1" Fill="#4682b4" Width="100" Height="100"/>
</Canvas>
<TextBlock Grid.Row="1" Grid.Column="0" Margin="10,0,0,0" TextWrapping="Wrap">Set the Rectangle Width:</TextBlock>
<ListBox Grid.Column="1" Grid.Row="1" Margin="10,0,0,0" Width="50" Height="50" SelectionChanged="changeWidth">
<ListBoxItem>25</ListBoxItem>
<ListBoxItem>50</ListBoxItem>
<ListBoxItem>75</ListBoxItem>
<ListBoxItem>100</ListBoxItem>
<ListBoxItem>125</ListBoxItem>
<ListBoxItem>150</ListBoxItem>
<ListBoxItem>175</ListBoxItem>
<ListBoxItem>200</ListBoxItem>
<ListBoxItem>225</ListBoxItem>
<ListBoxItem>250</ListBoxItem>
</ListBox>
<TextBlock Grid.Row="1" Grid.Column="2" Margin="10,0,0,0" TextWrapping="Wrap">Set the Rectangle MinWidth:</TextBlock>
<ListBox Grid.Column="3" Grid.Row="1" Margin="10,0,0,0" Width="50" Height="50" SelectionChanged="changeMinWidth">
<ListBoxItem>25</ListBoxItem>
<ListBoxItem>50</ListBoxItem>
<ListBoxItem>75</ListBoxItem>
<ListBoxItem>100</ListBoxItem>
<ListBoxItem>125</ListBoxItem>
<ListBoxItem>150</ListBoxItem>
<ListBoxItem>175</ListBoxItem>
<ListBoxItem>200</ListBoxItem>
<ListBoxItem>225</ListBoxItem>
<ListBoxItem>250</ListBoxItem>
</ListBox>
<TextBlock Grid.Row="1" Grid.Column="4" Margin="10,0,0,0" TextWrapping="Wrap">Set the Rectangle MaxWidth:</TextBlock>
<ListBox Grid.Column="5" Grid.Row="1" Margin="10,0,0,0" Width="50" Height="50" SelectionChanged="changeMaxWidth">
<ListBoxItem>25</ListBoxItem>
<ListBoxItem>50</ListBoxItem>
<ListBoxItem>75</ListBoxItem>
<ListBoxItem>100</ListBoxItem>
<ListBoxItem>125</ListBoxItem>
<ListBoxItem>150</ListBoxItem>
<ListBoxItem>175</ListBoxItem>
<ListBoxItem>200</ListBoxItem>
<ListBoxItem>225</ListBoxItem>
<ListBoxItem>250</ListBoxItem>
</ListBox>
以下后台代码示例处理 SelectionChanged 事件引发的事件。 每个自定义方法从 ListBox获取输入，将值分析为 Double，并将该值应用于指定的与宽度相关的属性。 宽度值也会转换为字符串，并写入各种 TextBlock 元素（所选 XAML 中未显示这些元素的定义）。
private void changeWidth(object sender, SelectionChangedEventArgs args)
{
ListBoxItem li = ((sender as ListBox).SelectedItem as ListBoxItem);
Double sz1 = Double.Parse(li.Content.ToString());
rect1.Width = sz1;
rect1.UpdateLayout();
txt1.Text = "ActualWidth is set to " + rect1.ActualWidth;
txt2.Text = "Width is set to " + rect1.Width;
txt3.Text = "MinWidth is set to " + rect1.MinWidth;
txt4.Text = "MaxWidth is set to " + rect1.MaxWidth;
}
private void changeMinWidth(object sender, SelectionChangedEventArgs args)
{
ListBoxItem li = ((sender as ListBox).SelectedItem as ListBoxItem);
Double sz1 = Double.Parse(li.Content.ToString());
rect1.MinWidth = sz1;
rect1.UpdateLayout();
txt1.Text = "ActualWidth is set to " + rect1.ActualWidth;
txt2.Text = "Width is set to " + rect1.Width;
txt3.Text = "MinWidth is set to " + rect1.MinWidth;
txt4.Text = "MaxWidth is set to " + rect1.MaxWidth;
}
private void changeMaxWidth(object sender, SelectionChangedEventArgs args)
{
ListBoxItem li = ((sender as ListBox).SelectedItem as ListBoxItem);
Double sz1 = Double.Parse(li.Content.ToString());
rect1.MaxWidth = sz1;
rect1.UpdateLayout();
txt1.Text = "ActualWidth is set to " + rect1.ActualWidth;
txt2.Text = "Width is set to " + rect1.Width;
txt3.Text = "MinWidth is set to " + rect1.MinWidth;
txt4.Text = "MaxWidth is set to " + rect1.MaxWidth;
}
Private Sub changeWidth(ByVal sender As Object, ByVal args As SelectionChangedEventArgs)
Dim li As ListBoxItem = CType(CType(sender, ListBox).SelectedItem, ListBoxItem)
Dim sz1 As Double = Double.Parse(li.Content.ToString())
rect1.Width = sz1
rect1.UpdateLayout()
txt1.Text = "ActualWidth is set to " + rect1.ActualWidth.ToString
txt2.Text = "Width is set to " + rect1.Width.ToString
txt3.Text = "MinWidth is set to " + rect1.MinWidth.ToString
txt4.Text = "MaxWidth is set to " + rect1.MaxWidth.ToString
End Sub
Private Sub changeMinWidth(ByVal sender As Object, ByVal args As SelectionChangedEventArgs)
Dim li As ListBoxItem = CType(CType(sender, ListBox).SelectedItem, ListBoxItem)
Dim sz1 As Double = Double.Parse(li.Content.ToString())
rect1.MinWidth = sz1
rect1.UpdateLayout()
txt1.Text = "ActualWidth is set to " + rect1.ActualWidth.ToString
txt2.Text = "Width is set to " + rect1.Width.ToString
txt3.Text = "MinWidth is set to " + rect1.MinWidth.ToString
txt4.Text = "MaxWidth is set to " + rect1.MaxWidth.ToString
End Sub
Private Sub changeMaxWidth(ByVal sender As Object, ByVal args As SelectionChangedEventArgs)
Dim li As ListBoxItem = CType(CType(sender, ListBox).SelectedItem, ListBoxItem)
Dim sz1 As Double = Double.Parse(li.Content.ToString())
rect1.MaxWidth = sz1
rect1.UpdateLayout()
txt1.Text = "ActualWidth is set to " + rect1.ActualWidth.ToString
txt2.Text = "Width is set to " + rect1.Width.ToString
txt3.Text = "MinWidth is set to " + rect1.MinWidth.ToString
txt4.Text = "MaxWidth is set to " + rect1.MaxWidth.ToString
End Sub
有关完整示例，请参阅 宽度属性比较示例。
