How to: Set the Width Properties of an Element
Example
This example visually shows the differences in rendering behavior among the four width-related properties in Windows Presentation Foundation (WPF).
The FrameworkElement class exposes four properties that describe the width characteristics of an element. These four properties can conflict, and when they do, the value that takes precedence is determined as follows: the MinWidth value takes precedence over the MaxWidth value, which in turn takes precedence over the Width value. The fourth property, ActualWidth, is read-only.
The following Extensible Application Markup Language (XAML) examples draw a Rectangle element (rect1) as a child of Canvas. You can change the width properties of a Rectangle by using a series of ListBoxes that represent the property values of MinWidth, MaxWidth, and Width. In this manner, the precedence of each property is visually displayed.
<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>
The following code-behind examples handle the events that the SelectionChanged event raises. Each custom method takes the input from the ListBox, parses the value as a Double, and applies the value to the specified width-related property. The width values are also converted to a string and written to a TextBlock element named txt1.
public 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;
}
public 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;
}
public 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;
}
Public 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
Public 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
Public 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
For the complete sample, see Width Properties Sample.
See Also
Tasks
How to: Set the Height Properties of an Element
Reference
MaxWidth
MinWidth
Width
ListBox
FrameworkElement
ActualWidth