swift - PMCreateSession 不创建打印 session

Question

尝试为 OS X 应用获取可打印的矩形。似乎涉及创建 session ，然后是页面格式，验证格式等。代码编译，但从 PMCreateSession 获得 -50 的状态。我是否不正确地声明了 printSession ？通常不必与 UnsafeMutablePointers 打交道。

谢谢!

    let printSession: UnsafeMutablePointer<PMPrintSession> = nil
    let pmPageFormat: UnsafeMutablePointer<PMPageFormat> = nil
    var status = PMCreateSession(printSession)
    status = PMCreatePageFormat(pmPageFormat)
    status = PMSessionDefaultPageFormat(printSession.memory, pmPageFormat.memory)
    let changed: UnsafeMutablePointer<DarwinBoolean> = nil
    status = PMSessionValidatePageFormat(printSession.memory, pmPageFormat.memory, changed)
    changed.destroy()
    var pRect = PMRect()
    status = PMGetAdjustedPageRect(pmPageFormat.memory, &pRect)

    Swift.print("pRect \(pRect)")

    status = PMRelease(pmPageFormat)
    status = PMRelease(printSession)

Answer 1

Am I declaring printSession improperly?

可以按如下方式获取 PMPrintSession:

// create a C Null pointer of type PMPrintSession
let printSession = unsafeBitCast(0, to: PMPrintSession.self)
// pass by & converts PMPrintSession to UnsafeMutablePointer<PMPrintSession>
PMCreateSession(&printSession)
…
// recast printSession to release memory
PMRelease( PMObject(printSession) )

或者，可以从 Cocoa NSPrintInfo 访问 PMPrintSession:

let printInfo = NSPrintInfo.shared()
let printSession = PMPrintSession(printInfo.pmPrintSession())

Normally don't have to deal so much with UnsafeMutablePointers

有关使用 UnsafeMutablePointer 的更多信息，请参阅 StackOverflow "How to use UnsafeMutablePointer in Swift?"

有关在 Swift 中使用 Core Printing 的完整示例，请参阅 004.42Apple_CorePrintingExample在 GitHub 上。