cocoa - NSView未收到mouseUp : event when mouse button is released outside of view

我有一个(例如)以下方法的自定义NSView子类:

override func mouseDown(with event: NSEvent) { Swift.print("mouseDown") }
override func mouseDragged(with event: NSEvent) { Swift.print("mouseDragged") }
override func mouseUp(with event: NSEvent) { Swift.print("mouseUp") }

只要在 View 内全部按下，拖动并释放鼠标(按钮)，就可以正常工作。但是，当在 View 内按下鼠标，在 View 外移动鼠标并释放鼠标时，我再也没有收到mouseUp事件。

附注:调用super实现没有帮助。

最佳答案

Apple的鼠标事件文档的Handling Mouse Dragging Operations部分提供了一种解决方案:显然，当使用鼠标跟踪循环跟踪事件时，确实会收到mouseUp事件。

这是文档中示例代码的一种变体，适用于Swift 3:

override func mouseDown(with event: NSEvent) {
    var keepOn = true

    mouseDownImpl(with: event)

    // We need to use a mouse-tracking loop as otherwise mouseUp events are not delivered when the mouse button is
    // released outside the view.
    while true {
        guard let nextEvent = self.window?.nextEvent(matching: [.leftMouseUp, .leftMouseDragged]) else { continue }
        let mouseLocation = self.convert(nextEvent.locationInWindow, from: nil)
        let isInside = self.bounds.contains(mouseLocation)

        switch nextEvent.type {
        case .leftMouseDragged:
            if isInside {
                mouseDraggedImpl(with: nextEvent)
            }

        case .leftMouseUp:
            mouseUpImpl(with: nextEvent)
            return

        default: break
        }
    }
}

func mouseDownImpl(with event: NSEvent) { Swift.print("mouseDown") }
func mouseDraggedImpl(with event: NSEvent) { Swift.print("mouseDragged") }
func mouseUpImpl(with event: NSEvent) { Swift.print("mouseUp") }

关于cocoa - NSView未收到mouseUp : event when mouse button is released outside of view，我们在Stack Overflow上找到一个类似的问题：https://stackoverflow.com/questions/40744161/