Element. Mouse Left Button Down 事件
在鼠标指针位于此元素上并且按下鼠标左键时发生。Occurs when the left mouse button is pressed while the mouse pointer is over this element.
public: virtual event System::Windows::Input::MouseButtonEventHandler ^ MouseLeftButtonDown;
public event System.Windows.Input.MouseButtonEventHandler MouseLeftButtonDown;
member this.MouseLeftButtonDown : System.Windows.Input.MouseButtonEventHandler
Public Custom Event MouseLeftButtonDown As MouseButtonEventHandler
尽管此 路由事件概述 看起来是通过元素树执行冒泡路由，但实际上它是一个直接路由事件，每个事件都沿着元素树进行 reraised ContentElement 。Although this Routed Events Overview seems to follow a bubbling route through an element tree, it actually is a direct routed event that is raised and reraised along the element tree by each ContentElement.
此事件是多个相关事件之一，用于报告基础事件的鼠标按钮细节 Mouse.MouseDown ，该事件是由事件路由中的每个元素处理的附加事件。This event is one of several related events that report the mouse-button specifics of an underlying Mouse.MouseDown event, which is an attached event that is processed by each element along an event route.
此事件的参数公开基础事件的参数 Mouse.MouseDown 。The arguments of this event expose the arguments of the underlying Mouse.MouseDown event. 如果该事件在事件路由中标记为 "已处理"，则仍会引发鼠标按钮特定的事件;但是，必须通过显式调用来添加鼠标按钮特定事件的处理程序 AddHandler ，并且可以选择处理已标记为已处理的事件，以便作为事件的侦听器。If that event is marked as handled along the event route, the mouse-button specific events are still raised; however, handlers of the mouse-button specific events must be added by explicitly calling AddHandler, with the option to handle events that are already marked as handled, in order to be listeners to the event.
从概念上讲，请将此事件的 (和) 上的其他鼠标按钮事件 ContentElement 为鼠标 "service" (，并使用类) 提供的服务定义 Mouse 。Conceptually, think of this event (and other mouse-button events on ContentElement) to be a mouse "service" (with the service definition provided by the Mouse class). 事件在事件数据中添加了不需要检查鼠标按钮状态 (的原始鼠标事件) 的便利。The event adds the convenience of not needing to check the mouse button states (left-right, up-down) of the original mouse events in the event data. 对于更高级的方案，如检查非标准按钮的状态，可能需要在 Mouse 类而不是上使用 api ContentElement 。For more advanced scenarios, such as checking for states of non-standard buttons, you might need to use the APIs on the Mouse class rather than those on ContentElement.
有些 ContentElement 具有类似于控件的行为的派生类（例如， Hyperlink ）可能具有鼠标按钮事件的固有类处理。A few ContentElement derived classes that have control-like behavior, for example, Hyperlink, might have inherent class handling for mouse button events. 鼠标左键按下事件是在控件中具有类处理的最可能的事件。The left mouse button down event is the most likely event to have class handling in a control. 类处理通常将基础 Mouse 类事件标记为已处理。The class handling often marks the underlying Mouse class event as handled. 将该事件标记为已处理后，通常不会引发附加到该元素的其他实例处理程序。Once the event is marked handled, other instance handlers that are attached to that element are not ordinarily raised. 通常也不会引发在冒泡方向上沿 UI 树中的根向下附加到元素的任何其他类或实例处理程序。Any other class or instance handlers that are attached to elements in the bubbling direction towards the root in the UI tree are also not ordinarily raised.
您可以 MouseLeftButtonDown 通过使用以下任一解决方案解决在具有类处理的派生类上的 "上一重要" 和 "接收鼠标左键按下事件" 事件中所述的问题：You can resolve the issue that is outlined in the preceding Important and still receive MouseLeftButtonDown events for left mouse button down events on a derived class that has class handling by using either of these solutions:
为事件附加处理程序 PreviewMouseDown ，这些处理程序未标记为由控件处理。Attach handlers for the PreviewMouseDown event, which is not marked as handled by the controls. 请注意，因为这是预览事件，所以路由从根节点开始，向下隧道到控件。Notice that because this is a preview event, the route starts at the root and tunnels down to the control.
通过调用 AddHandler 并选择允许处理程序侦听事件的签名选项（即使它们已在路由事件数据中标记为已处理），在控件过程上注册处理程序。Register a handler on the control procedurally by calling AddHandler and choosing the signature option that enables handlers to listen for events even if they are already marked as handled in the routed event data.
路由事件信息Routed Event Information
- 重写 OnMouseLeftButtonDown 以在派生类中实现此事件的类处理。Override OnMouseLeftButtonDown to implement class handling for this event in derived classes.