Saturday, 21 April 2012


Event Routing in WPF


Hi friends,

In this article you will know how to do event routing in  WPF .

1.     What is event

Events are messages that are send by an Object to notify the code that something occur
There are so many events in WPF like MouseEnter,MouseLeave , MouseMove etc

2.      WPF Event Handling

With WPF you can assign the event handler either wih XAML or in the Code Behid
The Event handling mechanism for WPF is based on .NET events
There is new concept like Routed event
               

There are 3 types of event routing in WPF

1.     Direct events
2.     Bubbling
3.     Tunneling

1. Direct event:

    • These are like ordinary .NET events.
    • They originate in one element and don’t pass to any other.
    • For example, MouseEnter (which fires when the mouse pointer moves over 
    • an element) is a direct event.
2. Bubbling events.

§  These events travel up the containment hierarchy.
§  For example, MouseDown is a bubbling event.
§  It’s raised first by the element that is clicked. Next, it’s raised by that element’s parent, then by that element’s parent, and so on, until WPF reaches the top of
 the element tree.

3. Tunneling events.

§  These events travel down the containment hierarchy.
§  They give you the chance to preview (and possibly stop) an event before it reaches the appropriate control.
§  For example, PreviewKeyDown allows you to intercept a key press, first at the window level and then in increasingly more specific containers until you 
reach the element that had focus when the key was pressed.
§  When there is Preview Keyword always Tunneling is done
§  The tunneling event always fires before the bubbling event.
§  To make life more interesting, if you mark the tunneling event as handled, the bubbling event won’t occur. That’s because the two events share the same instance of the RoutedEventArgs class.


Example:

Step 1.    Add a new WPF Window Project => Add Window, Name it RoutedEventDemo.xaml
Step 2.    Put the following xaml
Note: Preivew and Click events are being handled at all levels

<Window x:Class="IGatePatniApp.RoutedEventDemo"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    Title="Window4" Height="333" Width="550" Button.Click="Window_Click"
        PreviewMouseDown="Window_PreviewMouseDown"  PreviewMouseUp="Window_PreviewMouseUp">
    <Grid  PreviewMouseDown="Grid_PreviewMouseDown"  Button.Click="Grid_Click"
           PreviewMouseUp="Grid_PreviewMouseUp">
        <ListBox Margin="12,12,12,81" Name="listBox1" />
        <Button Margin="70,0,88,21"
                 PreviewMouseDown="btneventtest_PreviewMouseDown"  PreviewMouseUp="btneventtest_PreviewMouseUp"
                 Click="btneventtest_Click"
                Name="btneventtest" Height="30" VerticalAlignment="Bottom">Routed Event Test</Button>
    </Grid>
</Window>




Step 3.    The Event Handlers defined in the code behind


private void Window_PreviewMouseDown(object sender,
                                                                                                                MouseButtonEventArgs e)
        {
            listBox1.Items.Clear();
            listBox1.Items.Add("Window  " + e.RoutedEvent.Name);
        }
        private void Window_PreviewMouseUp(object sender,
                                                                                                                MouseButtonEventArgs e)
        {
            listBox1.Items.Add("Window  " + e.RoutedEvent.Name);
        }
        private void Grid_PreviewMouseDown(object sender,
                                                                                                                MouseButtonEventArgs e)
        {
            listBox1.Items.Add("Grid  " + e.RoutedEvent.Name);
        }
        private void Grid_PreviewMouseUp(object sender,
                                                                                                                MouseButtonEventArgs e)
        {
            listBox1.Items.Add("Grid  " + e.RoutedEvent.Name);
        }
        private void Grid_Click(object sender, RoutedEventArgs e)
        {
            listBox1.Items.Add("Grid  " + e.RoutedEvent.Name);
        }
        private void btneventtest_PreviewMouseDown(object sender,
                                                                                          MouseButtonEventArgs e)
        {
            listBox1.Items.Add("Button  " + e.RoutedEvent.Name);
        }
        private void btneventtest_PreviewMouseUp(object sender,
                                                                                                                MouseButtonEventArgs e)
        {
            listBox1.Items.Add("Button  " + e.RoutedEvent.Name);
        }
        private void btneventtest_Click(object sender, RoutedEventArgs e)
        {
            listBox1.Items.Add("Button  " + e.RoutedEvent.Name);
        }
        private void Window_Click(object sender, RoutedEventArgs e)
        {
            listBox1.Items.Add("Window  " + e.RoutedEvent.Name);
        }



Step 4.    Make this page as startup and run. click on the button and see the list of 
events in the listbox.




- After clicking button do not click anywhere because listbox will be reloaded with the 
new set of events

Good luck and please, let me know your feedback!
If you have any query mail me to Sujeet.bhujbal@gmail.com     

Regards
Sujeet Bhujbal


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 Blog:  www.sujitbhujbal.blogspot.com
Personal Website :- http://sujitbhujbal.wordpress.com/
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