如何读取通过引用传递的值的属性？

Question

我正在尝试编写OmniGraffle 5.3.6脚本，尝试读取传递给函数(或处理程序，用AppleScript术语)的canvas的layers元素。当我运行以下命令时：

on exportToPng(theCanvas)
    set layerCount to count of layers of theCanvas
end exportToPng

tell application "OmniGraffle Professional 5"
    set theDocument to front document
    set allCanvases to canvases of theDocument
    set theCanvas to item 1 of allCanvases
    my exportToPng(theCanvas)
end tell

我得到以下错误：

  error "OmniGraffle Professional 5 got an error: Can’t make |layers| of
  canvas id 1 of document \"base-dependency-diagram.graffle\" into type reference."
  number -1700 from |layers| of canvas id 1 of document
  "base-dependency-diagram.graffle" to reference

但是，如果我要内联我的函数，那么一切都很好：

tell application "OmniGraffle Professional 5"
    set theDocument to front document
    set allCanvases to canvases of theDocument
    set theCanvas to item 1 of allCanvases
    set layerCount to count of layers of theCanvas
end tell

我读过引用传递与值传递，但没有发现它有什么用。很稀疏。

Answer 1

你可以参考通过。但是，无论您传递到哪里，它也必须有"tell application“，以便应用程序能够处理传递的引用。所以你会想要这样的功能..。

on exportToPng(theCanvas)
    tell application "OmniGraffle Professional 5"
      set layerCount to count of layers of theCanvas
    end tell
end exportToPng

毕竟，只有"OmniGraffle专业5“知道如何从theCanvas中获取层。