Windows Presentation Foundation (WPF) Interview Questions and Answers

1 :: How can I use an application resource?

The following example shows an application definition file. The application definition file defines a resource section (a value for the Resources property). Resources defined at the application level can be accessed by all other pages that are part of the application. In this case, the resource is a declared style. Because a complete style that includes a control template can be lengthy, this example omits the control template that is defined within the ContentTemplate property setter of the style.

[XAML]
<Application.Resources>
<Style TargetType="Button" x:Key="GelButton" >
<Setter Property="Margin" Value="1,2,1,2"/>
<Setter Property="HorizontalAlignment" Value="Left"/>
<Setter Property="Template">
<Setter.Value>

...

</Setter.Value>
</Setter>
</Style>
</Application.Resources>

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2 :: How can I set an attached property in code?

The following example shows how you can set an attached property in code.

[C#]

DockPanel myDockPanel = new DockPanel();
CheckBox myCheckBox = new CheckBox();
myCheckBox.Content = "Hello";
myDockPanel.Children.Add(myCheckBox);
DockPanel.SetDock(myCheckBox, Dock.Top);

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3 :: How can I mark the default value of a custom dependency property to be false?

Here is an example :

[C#]

public class MyStateControl : ButtonBase
{
public MyStateControl() : base() { }
public Boolean State
{
get { return (Boolean)this.GetValue(StateProperty); }
set { this.SetValue(StateProperty, value); }
}
public static readonly DependencyProperty StateProperty = DependencyProperty.Register(
"State", typeof(Boolean), typeof(MyStateControl),new PropertyMetadata(false));
}

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4 :: How can I create Custom Read-Only Dependency Properties?

The typical reason for specifying a read-only dependency property is that these are the properties that is used to determine the state, but where the state is defined in a multitude of factors. A typical example for a read-only property is IsMouseHover

This example shows how to 'register' an attached property as read-only. You can use dependency properties on any 'DependencyObject' types.

[C#]
public static readonly DependencyProperty IsBubbleSourceProperty = DependencyProperty.RegisterReadOnly(
"IsBubbleSource",
typeof(Boolean),
typeof(AquariumObject),
new FrameworkPropertyMetadata(false, FrameworkPropertyMetadataOptions.AffectsRender)
);

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5 :: How can I enumerate all the descendants of a visual object?

You can enumerate all the descendants of a visual object as follows :

[C#]

// Enumerate all the descendants of the visual object.
static public void EnumVisual(Visual myVisual)
{
for (int i = 0; i < VisualTreeHelper.GetChildrenCount(myVisual); i++)
{
// Retrieve child visual at specified index value.
Visual childVisual = (Visual)VisualTreeHelper.GetChild(myVisual, i);

// Do processing of the child visual object.

// Enumerate children of the child visual object.
EnumVisual(childVisual);
}
}

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