Visual Basic and WPF Event Handling
For the Microsoft Visual Basic .NET language specifically, you can use the language-specific Handles keyword to associate event handlers with instances, instead of attaching event handlers with attributes or using the AddHandler method. No entanto, o Handles técnica para anexar manipuladores para instâncias tem algumas limitações, porque o Handles sintaxe não oferece suporte a algumas das específicas roteados eventos recursos da WPF sistema de eventos.
Using "Handles" in a WPF Application
The event handlers that are connected to instances and events with Handles must all be defined within the partial class declaration of the instance, which is also a requirement for event handlers that are assigned through attribute values on elements. You can only specify Handles for an element on the page that has a Name property value (or x: nome de diretiva declared). Isso ocorre porque o Name em XAML cria a referência de instância é necessária para dar suporte a Instance.Event formato de referência exigido pelo Handles sintaxe. The only element that can be used for Handles without a Name reference is the root-element instance that defines the partial class.
You can assign the same handler to multiple elements by separating Instance.Event references after Handles with commas.
You can use Handles to assign more than one handler to the same Instance.Event reference. Do not assign any importance to the order in which handlers are given in the Handles reference; you should assume that handlers that handle the same event can be invoked in any order.
To remove a handler that was added with Handles in the declaration, you can call RemoveHandler.
You can use Handles to attach handlers for routed events, so long as you attach handlers to instances that define the event being handled in their members tables. For routed events, handlers that are attached with Handles follow the same routing rules as do handlers that are attached as XAML attributes, or with the common signature of AddHandler. This means that if the event is already marked handled (the Handled property in the event data is True), then handlers attached with Handles are not invoked in response to that event instance. The event could be marked handled by instance handlers on another element in the route, or by class handling either on the current element or earlier elements along the route. For input events that support paired tunnel/bubble events, the tunneling route may have marked the event pair handled. For more information about routed events, see Visão geral sobre eventos roteados.
Limitations of "Handles" for Adding Handlers
Handles cannot reference handlers for attached events. You must use the add accessor method for that attached event, or typename.eventname event attributes in XAML. For details, see Visão geral sobre eventos roteados.
For routed events, you can only use Handles to assign handlers for instances where that event exists in the instance members table. However, with routed events in general, a parent element can be a listener for an event from child elements, even if the parent element does not have that event in its members table. In attribute syntax, you can specify this through a typename.membername attribute form that qualifies which type actually defines the event you want to handle. For instance, a parent Page (with no Click event defined) can listen for button-click events by assigning an attribute handler in the form Button.Click. But Handles does not support the typename.membername form, because it must support a conflicting Instance.Event form. For details, see Visão geral sobre eventos roteados.
Handles cannot attach handlers that are invoked for events that are already marked handled. Instead, you must use code and call the handledEventsToo overload of AddHandler(RoutedEvent, Delegate, Boolean).
Observação
Não use o Handles sintaxe em Visual Basic código quando você especificar um manipulador de eventos para o mesmo evento em XAML.Nesse caso, o manipulador de evento é chamado duas vezes.
How WPF Implements "Handles" Functionality
Quando um Extensible Application Markup Language (XAML) o arquivo intermediário de página é compilada, declara Friend WithEvents referências para cada elemento na página que tem um Name conjunto de propriedades (ou x: nome de diretiva declarado). Each named instance is potentially an element that can be assigned to a handler through Handles.
Observação
Within Microsoft Visual Studio, IntelliSense can show you completion for which elements are available for a Handles reference in a page.However, this might take one compile pass so that the intermediate file can populate all the Friends references.
Consulte também
Referência
Conceitos
Marcando Eventos Roteados como Manipulados e Manipulação de Classes