如何在Swift中将“自我”传递给接受“不安全突变的function”的函数？

Question

我去年买了一台3D 4K投影仪，它使用了DLP-Link技术，它需要一个120 for左右交替的视频流来进行立体透视。

我正在使用核心视频在Swift中编写一个播放器，一个函数要求我向它传递一个UnsafeMutableRawPointer? (void * in Obj-C)，并且我使用self关键字将视图实例传递给它。

这是我的密码：

//
//  MovieView.swift
//  Studio Media Player
//
//  Created by DannyNiu on 2022-07-03.
//

import Foundation
import Cocoa

import AVFoundation
import CoreVideo

class MovieView : NSView
{
    var asset: AVAsset?
    var player: AVPlayer?
    var item: AVPlayerItem?
    var vout: AVPlayerItemVideoOutput?
    var cvpb: CVPixelBuffer?
    var cii: CIImage?
    var cgi: CGImage?
    var irect: CGRect?
    var vlink: CVDisplayLink?
    
    func setup_displaylink() -> Bool
    {
        var cvret: CVReturn
        
        cvret = CVDisplayLinkCreateWithActiveCGDisplays(&vlink)
        if( vlink == nil ) { return false }
        
        var me: MovieView = self
        cvret = CVDisplayLinkSetOutputCallback(
            vlink!, vlink_callback, &me)
        
        if( cvret == kCVReturnSuccess ) {
            return true
        } else { return false }
    }
    
    func assign_asset(_ asset: AVAsset)
    {
        self.asset = asset
        item = .init(asset: asset)
        player = .init(playerItem: item)
        vout = .init()
        cvpb = nil
        cii = nil
    }
    
    func video_render(_ d: CVTimeStamp)
    {
        let t: CMTime = player!.currentTime()
        
        let cgc: CGContext = (NSGraphicsContext.current?.cgContext)!
        let cic: CIContext = (NSGraphicsContext.current?.ciContext)!
        
        if( vout?.hasNewPixelBuffer(forItemTime: t) ?? false )
        {
            cvpb = vout?.copyPixelBuffer(
                forItemTime: t, itemTimeForDisplay: nil)
            cii = .init(cvPixelBuffer: cvpb!)
            irect = cii!.extent
            cgi = cic.createCGImage(cii!, from: irect!)
        }
        
        if( irect == nil ) { return }
        
        let orect: CGRect = NSRectToCGRect(bounds)
        var vrect: CGRect =
        CGRect(origin: orect.origin,
               size: CGSize(width: orect.width * 2,
                            height: irect!.height *
                                    orect.width /
                                    irect!.width))
        
        cgc.setFillColor(gray:0, alpha:1)
        cgc.fill(orect)
        
        if( d.videoTime % 2 == 1 )
        {
            vrect = vrect.offsetBy(dx: -orect.width, dy: 0)
        }
        cgc.draw(cgi!, in: vrect)
    }
}

func vlink_callback(
    displayLink: CVDisplayLink,
    inNow: UnsafePointer<CVTimeStamp>,
    inOutputTime: UnsafePointer<CVTimeStamp>,
    flagsIn: CVOptionFlags,
    flagsOut: UnsafeMutablePointer<CVOptionFlags>,
    arg_mvview: UnsafeMutableRawPointer?
) -> CVReturn
{
    let mvview: MovieView = arg_mvview!.load(as: MovieView.self)
    mvview.video_render(inNow.pointee)
    
    return kCVReturnSuccess
}

当我调试程序时，mvview.video_render(inNow.pointee)行使用code = 1导致了一个EXC_BAD_ACCESS陷阱。我认为这是由于我没有正确地将self传递给显示链接回调造成的。那我该怎么解决呢？

Answer 1

使用Unmanaged类。

在setup_displaylink()中

    func setup_displaylink() -> Bool
    {
        var cvret: CVReturn
        
        cvret = CVDisplayLinkCreateWithActiveCGDisplays(&vlink)
        if( vlink == nil ) { return false }
        
        var me: UnsafeMutableRawPointer = 
        Unmanaged.passUnretained(self).toOpaque()
        cvret = CVDisplayLinkSetOutputCallback(
            vlink!, vlink_callback, &me)
        
        if( cvret == kCVReturnSuccess ) {
            return true
        } else { return false }
    }

在vlink_callback中

func vlink_callback(
    displayLink: CVDisplayLink,
    inNow: UnsafePointer<CVTimeStamp>,
    inOutputTime: UnsafePointer<CVTimeStamp>,
    flagsIn: CVOptionFlags,
    flagsOut: UnsafeMutablePointer<CVOptionFlags>,
    arg_mvview: UnsafeMutableRawPointer?
) -> CVReturn
{
    let mvview: MovieView =
    Unmanaged.fromOpaque(arg_mvview!).takeUnretainedValue()
    mvview.video_render(inNow.pointee)
    
    return kCVReturnSuccess
}

注意，我使用了“未保留”函数，因为没有必要添加到电影视图的引用计数中，因为self是在内部传递的。在适当的情况下使用“保留”函数。