| Silverlight
does not have as much support to handle events from unreferenced child
controls as WPF. For example, say you have the following control
hierarchy and
Page needs to handle events from the Child Controls.
This
is easy in WPF since you can use commands,
or
UIElement.AddHandler.
For example:
public MainWindow()
{
InitializeComponent();
// subscribe to events
raised by any child, Child Control is a Button in this example
this.AddHandler(Button.ClickEvent, new RoutedEventHandler(ChildClicked));
}
private void ChildClicked(object sender, RoutedEventArgs e)
{
// called when event is raised by any child
}
Or
you can declare the event handler in XAML.
<Window x:Class="WpfEvents.MainWindow"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:controls="clr-namespace:WpfEvents"
Title="WPF Events" Height="200" Width="200"
Button.Click="ChildClicked">
Back
to Silverlight, it
does not support commands or UIElement.AddHandler. There are several
options:
Hookup each event handler
You can specify the event handler for each child control but that is
the whole point... we want to handle events
even though we don't have a reference to the individual child controls.
//
hooking up events requires a reference to each control
this.ChildControl1.Click += new RoutedEventHandler(ChildControl1_Click);
this.ChildControl2.Click += new RoutedEventHandler(ChildControl2_Click);
this.ChildControl3.Click += new RoutedEventHandler(ChildControl3_Click);
this.ChildControl4.Click += new RoutedEventHandler(ChildControl4_Click);
Bubble
up
the events
You can write code that bubbles up the events (re-raises the events).
This usually becomes undesirable, especially when you have controls
nested at several levels.
Use global Events class
One option is to create a global Events class.
- There
is only one instance of the Events class in the application.
- It
contains a list of global events and helper methods to raise the events.
- Any
object can subscribe to events.
- Any
object can raise events.
- That
means the main page can handle events from any child control, children
can handle events from the main page, and siblings can handle events
from each other.
- A
reference to the control is not required to handle events.
Example
Events class.
public static class Events
{
// example global event that can be handled
by any object in the application
public static event EventHandler ChildControlClicked;
public static void RaiseChildControlClicked(object sender, EventArgs args)
{
if (ChildControlClicked != null)
{
ChildControlClicked(sender,args);
}
}
}
Example
of raising an event.
// raise global event
Events.RaiseChildControlClicked(this, EventArgs.Empty);
Example
of handling an event.
public Page()
{
InitializeComponent();
// subscribe to global event
Events.ChildControlClicked += new System.EventHandler(Events_ChildControlClicked);
}
private void Events_ChildControlClicked(object sender, System.EventArgs e)
{
// called when the event is raised, it could be raised by
// any object in the
application, this object does not need
// a reference to the object that raised
the event
}
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