ios - 如何在 Swift 中的转义 block 内正确访问 self

Question

我在下面的代码中遇到了一些崩溃。我认为崩溃是由 block (LoadXZYAPI)转义和已释放的 ViewControllerA 的访问属性引起的。因此，当访问strongSelf.data.*时，strongSelf返回nil或在dealloc内存位置并导致崩溃。

有什么方法可以防止这种崩溃，而无需在每次尝试访问其属性(data.*)时检查strongSelf？在这种情况下，在不使 LoadXZYAPI 不转义的情况下，最佳实践是什么？

提前致谢

class ViewControllerA {

        var data: [String: Any]?

        func loadData(){

            LoadXZYAPI() { [weak self] (data:Any?) in

                if let strongSelf = self {

                    strongSelf.data = data

                    DispatchQueue.global(qos:.default).asyc {

                        // process self.data
                        let imageData = GetImageData(data:strongSelf.data["image_name"])

                        if let data = data, let image = UIImage(data:imageData) {

                            DispatchQueue.main.async {
                                strongSelf.imageView = nil

                                strongSelf.imageView = CustomView(image: image) <-- Crashes randomly after this line
                                strongSelf.imageView!.width = strongSelf.map["width"] as? CGFloat
                                strongSelf.imageView!.height = strongSelf.map["height"] as? CGFloat
                                strongSelf.imageView!.backgroundColor = UIColor.init(hex: "#efefef")
                                strongSelf.imageViewWrapper.addSubview((strongSelf.imageView)!)
                                strongSelf.imageViewWrapper.bringSubview(toFront: (strongSelf.imageView)!)
                                strongSelf.imageView!.translatesAutoresizingMaskIntoConstraints = false
                                NSLayoutConstraint.activate([
                                    (strongSelf.imageView?.leadingAnchor)!.constraint(equalTo: (strongSelf.imageViewWrapper?.leadingAnchor)!),
                                    (strongSelf.imageView?.trailingAnchor)!.constraint(equalTo: (strongSelf.imageViewWrapper?.trailingAnchor)!),
                                    (strongSelf.imageView?.topAnchor)!.constraint(equalTo: (strongSelf.navigationController?.navigationBar.bottomAnchor)!),
                                    (strongSelf.imageView?.bottomAnchor)!.constraint(equalTo: (strongSelf.imageViewWrapper?.bottomAnchor)!),
                                    ])

                                self?.didUpdateImageView()
                            }
                        }
                    }
                }
            }
        }
    }

Answer 1

这应该是安全的:

func loadData(){

    LoadXZYAPI() { [weak self] (data:Any?) in

        //didn't bother putting a guard here since you don't need a strong ref here
        self?.data = data

        DispatchQueue.global(qos:.default).asyc {

            guard let strongSelf1 = self else {
                return
            }

            //use strongSelf1

            DispatchQueue.main.async {

                guard let strongSelf2 = self else {
                    return
                }

                //use strongSelf2
            }
        }
    }
}