How to: Convert a ListBoxItem to a New Data Type
This example shows how to convert the contents of a ListBoxItem to an instance of Thickness. Although this example specifically shows how to convert a ListBoxItem into an instance of Thickness, it also shows how you can use any compatible type converter to convert a ListBoxItem.
Example
The following example creates a ListBox element that has ten selectable ListBoxItem objects. The SelectionChanged event triggers the ChangeMargin custom method, which the subsequent code example defines.
In the Extensible Application Markup Language (XAML) example, each ListBoxItem represents a Thickness value, which is used to describe the uniform margins of an element. However, before you can use a ListBoxItem to represent an instance of Thickness, you must first convert it to the correct data type. The subsequent code example shows the conversion.
<ListBox Grid.Row="0" Grid.Column="1"
Width="50" Height="50"
VerticalAlignment="Top"
SelectionChanged="ChangeMargin">
<ListBoxItem>10</ListBoxItem>
<ListBoxItem>20</ListBoxItem>
<ListBoxItem>30</ListBoxItem>
<ListBoxItem>40</ListBoxItem>
<ListBoxItem>50</ListBoxItem>
<ListBoxItem>60</ListBoxItem>
<ListBoxItem>70</ListBoxItem>
<ListBoxItem>80</ListBoxItem>
<ListBoxItem>90</ListBoxItem>
<ListBoxItem>100</ListBoxItem>
</ListBox>
When a user changes the ListBox selection, the change invokes the event handler ChangeMargin. This method passes the ListBoxItem to a ThicknessConverter object, which converts the Content property of the ListBoxItem to an instance of Thickness. (Notice that the value of Content has already been converted to a string by using the ToString method.) This value is then set to the Margin of the text1 object.
Private Sub ChangeMargin(ByVal sender As Object, ByVal args As SelectionChangedEventArgs)
Dim li As ListBoxItem = CType(CType(sender, ListBox).SelectedItem, ListBoxItem)
Dim myThicknessConverter As ThicknessConverter = New ThicknessConverter()
Dim th1 As Thickness = CType(myThicknessConverter.ConvertFromString(li.Content.ToString()), Thickness)
text1.Margin = th1
Dim st1 As String = CType(myThicknessConverter.ConvertToString(text1.Margin), String)
gridVal.Text = "The Margin property is set to " + st1 + "."
End Sub
private void ChangeMargin(object sender, SelectionChangedEventArgs args)
{
ListBoxItem li = ((sender as ListBox).SelectedItem as ListBoxItem);
ThicknessConverter myThicknessConverter = new ThicknessConverter();
Thickness th1 = (Thickness)myThicknessConverter.ConvertFromString(li.Content.ToString());
text1.Margin = th1;
String st1 = (String)myThicknessConverter.ConvertToString(text1.Margin);
gridVal.Text = "The Margin property is set to " + st1 +".";
}
For the complete sample, see Changing Margins in a Grid Sample.
See Also
Tasks
How to: Change the Margin Property
How to: Use a ThicknessConverter Object