Cocoa 从菜单项调用popover崩溃

我有一个工具栏按钮

@IBOutlet weak var testButton: NSToolbarItem!

这个按钮叫popover，效果很好

但是如果我试着从最上面的菜单项调用popover，我会崩溃。 我已经修改了popover的位置，使其显示在testButton的下方，与正常情况一样。评论如下

@IBAction func menuPreviewAndTestAction(sender: AnyObject) {
    var returnedHtmlString = checkEverythingAndCreateTheEncodedHtml(testButton)
    setEncodedHtmlToPreview(returnedHtmlString)
    var thebounds = self.testButton.view?.bounds // so i am givving bounds of button that narmally calls poover
    testingPopover.showRelativeToRect(thebounds!, ofView: sender as NSView, preferredEdge: NSMaxYEdge) // crashes
}

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哦，天哪。。。我错过了更改ofView的机会，所有这些都与以下内容排序：

var thebounds = self.testButton.view?.bounds
        var theview = self.testButton.view
        testingPopover.showRelativeToRect(thebounds!, ofView: theview! as NSView,      preferredEdge: NSMaxYEdge)