Introduction

(View this article in Code Project)

We used to see a Notification tool tip in Windows 7/Vista to inform something about particular context. For example, Capslock warning will be given through a balloon tip on Passwordbox, if capslock has ON. Or sometimes low battery information will be displayed on the Taskbar.
Password.png
The unique feature of this control will be that it can be placed on any Framework Element in Silverlight.

Background

Using the code

The base class for Notification control is Content Control. The content can be of anything like a string, image, etc. The control will be displayed on any FrameworkElement in Silverlight. A popup is used to host the actual control and the popup will be placed on particular element based on its position.
The generic template XAML goes like this,

<Style TargetType="local:Balloon">
        <Setter Property="FontSize" Value="13"/>
        <Setter Property="Template">
            <Setter.Value>
                <ControlTemplate TargetType="local:Balloon">
                    <Grid>
                        <Grid.Effect>
                            <DropShadowEffect ShadowDepth="2" Direction="315"/>
                        </Grid.Effect>
                        <Grid.RowDefinitions>
                            <RowDefinition Height="*"/>
                            <RowDefinition Height="Auto"/>
                            <RowDefinition Height="Auto"/>
                        </Grid.RowDefinitions>
                        <Border Grid.Row="1" BorderBrush="Gray" BorderThickness="1" CornerRadius="5"
                                Margin="{Binding Alignment, Converter={StaticResource Converter}, 
                                RelativeSource={RelativeSource TemplatedParent}, ConverterParameter=MainMargin}">
                            <Border.Background>
                                <LinearGradientBrush EndPoint="0.5,1" StartPoint="0.5,0">
                                    <GradientStop Color="#FFE7E8F1" Offset="1"/>
                                    <GradientStop Color="White"/>
                                    <GradientStop Color="#FFF3F4F6" Offset="0.472"/>
                                </LinearGradientBrush>
                            </Border.Background>
                            <Grid>
                                <Grid.ColumnDefinitions>
                                    <ColumnDefinition Width="Auto"/>
                                    <ColumnDefinition Width="*"/>
                                </Grid.ColumnDefinitions>
                                <Grid.RowDefinitions>
                                    <RowDefinition Height="Auto"/>
                                    <RowDefinition Height="*"/>
                                </Grid.RowDefinitions>
                                <Image Source="{TemplateBinding Icon}" Margin="5"/>
                                <TextBlock Margin="5" Grid.Column="1" Foreground="#FF28489F" Text="{TemplateBinding Header}" FontSize="16"
                                           VerticalAlignment="Center"/>
                                <ContentPresenter Margin="5" Grid.Column="1" Grid.Row="1"/>
                            </Grid>
                        </Border>
                        
                        <Path Data="M306.375,133.125L306.375,100.875L335.75,133.25" Stroke="Gray" Height="20" 
                              Fill="White" Margin="{Binding Alignment, Converter={StaticResource Converter}, 
                              RelativeSource={RelativeSource TemplatedParent}, ConverterParameter=Margin}"
                              StrokeThickness="1" Stretch="Uniform" Visibility="{Binding Alignment, Converter={StaticResource Converter},
                              RelativeSource={RelativeSource TemplatedParent}, ConverterParameter=bottom}" VerticalAlignment="Center" 
                              HorizontalAlignment="{Binding Alignment, Converter={StaticResource Converter}, 
                              RelativeSource={RelativeSource TemplatedParent}, ConverterParameter=Alignment}"/>

                        <Path Data="M306.375,133.125L306.375,100.875L335.75,133.25" Stroke="Gray" 
                              Height="20" Fill="#FFE7E8F1" Margin="{Binding Alignment, Converter={StaticResource Converter}, 
                              RelativeSource={RelativeSource TemplatedParent}, ConverterParameter=Margin}"
                              StrokeThickness="1" Stretch="Uniform" Grid.Row="2" Visibility="{Binding Alignment, 
                              Converter={StaticResource Converter}, RelativeSource={RelativeSource TemplatedParent}, ConverterParameter=top}"
                              VerticalAlignment="Center" RenderTransformOrigin="0.5, 0.5" HorizontalAlignment="{Binding Alignment, 
                              Converter={StaticResource Converter},
                              RelativeSource={RelativeSource TemplatedParent}, ConverterParameter=Alignment}">
                            <Path.RenderTransform>
                                <ScaleTransform ScaleY="-1"/>
                            </Path.RenderTransform>
                        </Path>
                    </Grid>
                </ControlTemplate>
            </Setter.Value>
        </Setter>
    </Style>

Balloon Alignment 

To position the Popup on particular location in the control, the co-ordinates related to Browser needs to be find out. This can be done using GeneralTransform. The Alignment property in the control helps change the place where popup needs to be hosted.
It can be of one among the following,

   public enum BalloonAlignment
    {
        TopLeft,

        TopRight,

        BottomLeft,

        BottomRight
    }

Ballon Tooltip Service

An attached property of type DependencyObject should be added to a static class, which can be used to set balloon on any DependecyObject. The object can be textBox, Checkbox, Combobox, etc.
public static class BalloonTooltipService
    {
        public static Balloon GetBalloonTooltip(DependencyObject obj)
        {
            return (Balloon)obj.GetValue(BalloonTooltipProperty);
        }

        public static void SetBalloonTooltip(DependencyObject obj, Balloon value)
        {
            obj.SetValue(BalloonTooltipProperty, value);
        }

        // Using a DependencyProperty as the backing store for BalloonTooltip.  This enables animation, styling, binding, etc...
        public static readonly DependencyProperty BalloonTooltipProperty =
            DependencyProperty.RegisterAttached("BalloonTooltip",  
            typeof(Balloon), typeof(BalloonTooltipService), 
            new PropertyMetadata(null, new PropertyChangedCallback(OnBalloonToolTipChanged)));

        private static void OnBalloonToolTipChanged(DependencyObject sender, DependencyPropertyChangedEventArgs args)
        {
            var element = sender as FrameworkElement;
            Balloon tooltip = args.NewValue as Balloon;
            if (tooltip != null)
            {
                tooltip.DataContext = element.DataContext;
                tooltip.Target = element;
            }
        }
    }
Checkbox.png

Application Usage

The control can be used in application to show some usefull information about the particular context. Following code shows how to set balloon using BallonTooltipService.
           <CheckBox VerticalAlignment="Center" Width="100"  Margin="3" GotFocus="OnFocus">
                <balloon:BalloonTooltipService.BalloonTooltip>
                    <balloon:Balloon x:Name="balloon1" Header="Checkbox Notification" 
                         HorizontalAlignment="Center" Alignment="{Binding Path=SelectedValue}" 
                         VerticalAlignment="Center" Icon="WarningHS.png">
                        <balloon:Balloon.Content>
                            <Grid>
                                <TextBlock TextWrapping="Wrap" 
                           Text="Balloon can be placed on any Framework Element."/>
                            </Grid>
                        </balloon:Balloon.Content>
                    </balloon:Balloon>
                </balloon:BalloonTooltipService.BalloonTooltip>
            </CheckBox> 
  
Sample Link:
http://www.codeproject.com/KB/silverlight/320232/BalloonDemo.zip
 
Source Code:
http://www.codeproject.com/Articles/320232/Notification-Control-in-Silverlight