User interface elements UIElements have the ability to nest elements. A panel can contain a button which can contain a panel. Within that panel could be an image and some text. The user then clicks the mouse button. What element is expected to handle the event? Is it the text or the image? It could even be the panel that holds them or the button itself.
A common practice is to add a mouse click handler for a specific UIElement. The code may look something like this:. This type of event routing is called Direct. It is more exactly RoutingStrategy. In this implementation, the concept of Routed Events is invisible to the developer. Continuing with this example, if you wanted to handle the click for an image and a text block and the button with the same action, you could add handlers on the image, textblock, stackpanel, and the button, or you could use routed events.
The tutorial in this post will guide you through creating a project that will visually demonstrate the flow, or routing, of events.
It is interesting to see the flow of events, both up and down the visual tree of the window. Direct events are most common and are used when you specify a handler on a specific UIElement. An example is when you handle the Click event on a button.
The event will be handled by that specific handler. Bubbling events are events that get routed up the element hierarchy from the source of the event to each successive parent element until the root element of the page, the base of the element hierarchy, is reached. Tunneling events are those that start at the root of the element hierarchy and travel downwards through each successive child element until the element that invoked the event is reached. Tunneling events are also referred to as Preview events because of the naming convention used for handler methods, such as PreviewMouseDown and PreviewMouseUp.
The Preview prefix helps differentiate in which direction the event will be handled. Events are often created in pairs of bubbling and tunneling events, with the tunneling event having the Preview prefix on its method name. This is done to enable each input action to invoke both a bubbling and tunneling event. Visual Studio with the following workloads and individual components:.
You should have a general knowledge of Visual Studio and the C language syntax. You will be adding and editing files, and debugging code.
Given below is a simple example of a Routed event in which a button and three text blocks are created with some properties and events. If you want to stop the routed event at any particular level, then you will need to set the e. When you click on the button, you will observe that the click event will not be routed to the window and will stop at the stackpanel and the 3 rd text block will not be updated.
NET framework, custom routed event can also be defined. You need to follow the steps given below to define a custom routed event in C. Given below is the C code for the MyCustomControl class which inherits from the Control class in which a custom routed event Click is created for the custom control. So, you'll have a previewMouseDown and then a MouseDown event. Event Sequence. A standard Button control is derived from ButtonBase, and so it inherits a Click event that fires when a user clicks on the button.
But as the Button does something in response to button presses, it swallows the bubbling events e. In general, controls that do something as the result of a user pressing a mouse button will swallow the related events.
Clicking on a TextBox gives it focus. Clicking on a Button or ComboBox also results in the control responding to the click, so these controls also swallow the non-preview events. Remember, these types of controls only fire the Tunneling events. When a user clicks on a button, there are a series of preview events tunneling and actual events bubbling that travel up and down the logical tree.
But for a Label contained in a StackPanel, which is contained in a Window, the full sequence of events for a left mouse button click on the Label is,.
Now get ready for some hands-on demo of this beautiful feature of routed events. Very soon I will post few more examples on Tunneling events as well. Many of the easy tutorials available on the internet provide examples based on buttons. It is very basic and easy and it hides the important aspects of using the Routed events. So, I have decided to use controls other than buttons more specifically TextBlock!
Hands-on Demo. Here I will create a custom routed event. You need to follow the steps given below to define a custom routed event in C. Given below is the C code for the MyCustomControl class which inherits from the Control class in which a custom routed event Click is created for the custom control. The code is heavily commented in order to spoon-feed you with the logic.
If you are clear up to here, you are more or less through. Routed events are events which navigate up or down the visual tree acording to their RoutingStrategy. The routing strategy can be bubble, tunnel or direct. You can hook up event handlers on the element that raises the event or also on other elements above or below it by using the attached event syntax: Button. Routed events normally appear as pair. The first is a tunneling event called PreviewMouseDown and the second is the bubbling called MouseDown.
They don't stop routing if the reach an event handler. To stop routing then you have to set e. By naming convention it is called Preview Bubbling The event is raised on the source element and navigates up to the visual tree until it reaches the root element or until the bubbling is stopped by marking the event as handled. The bubbling event is raised after the tunneling event.
Direct The event is raised on the source element and must be handled on the source element itself. This behavior is the same as normal. NET events. Home Fundamentals Routed Events. NET 4. SelectedEvent ;.
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