swift – 是否有必要解除分配AutoreleasingUnsafeMutablePointer?如果是这样,怎么样?

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使用ARC,我可以将对象的所有强引用设置为nil以释放它.

使用UnsafePointer或UnsafeMutablePointer,我需要显式管理其内存:

let buffer = sizeof(Int8) * 4
var ptr = UnsafeMutablePointer<Void>.alloc(buffer)
defer {
    ptr.destroy()
    ptr.dealloc(someVal)
    ptr = nil
}

但是对于AutoreleasingUnsafeMutablePointer对象,文档是不明确的.我无法在AutoreleasingUnsafeMutablePointer上显式调用destroy或dealloc.

var ptr: AutoreleasingUnsafeMutablePointer<Void> = nil
defer {
    ptr = nil
}

// assign something to ptr

名称暗示它在超出范围后自动释放,但是我是否需要将AutoreleasingUnsafeMutablePointer设置为nil才能自动释放?

这是一个示例,我使用AutoreleasingUnsafeMutablePointer来获取运行时当前加载的所有类的列表.请注意,在调用Objective-C运行时的功能时,某些函数需要AutoreleasingUnsafeMutablePointer而不仅仅是UnsafeMutablePointer:

var numClasses: Int32 = 0
var allClasses: AutoreleasingUnsafeMutablePointer<AnyClass?> = nil
defer {
    allClasses = nil // is this required?
}

numClasses = objc_getClassList(nil,0)

if numClasses > 0 {
    var ptr = UnsafeMutablePointer<AnyClass>.alloc(Int(numClasses))
    defer {
        ptr.destroy()
        ptr.dealloc(Int(numClasses))
        ptr = nil
    }
    allClasses = AutoreleasingUnsafeMutablePointer<AnyClass?>.init(ptr)
    numClasses = objc_getClassList(allClasses,numClasses)

    for i in 0 ..< numClasses {
        if let currentClass: AnyClass = allClasses[Int(i)] {
            print("\(currentClass)")
        }
    }
}
您不需要将其设置为nil.它应该由一个自动释放的指针构造(假设它被正确构造,它将自行释放).同时,不要抓住它超过当前的堆栈框架. AutoreleasingUnsafeMutablePointer不会使对象保持活动状态.弹出封闭的自动释放池时,将释放包装的对象并可能已取消分配.就像这个名字所说:它是不安全的.

通过永远不在Swift中自己创建AutoreleasingUnsafeMutablePointer来避免问题(编辑:除非它真的是一个UnsafeMutablePointer并且C头导入出错了,见下文).如果你正确使用它,它应该是Swift的inout和Objective-C返回指针参数之间的透明胶水.

您通常会创建一个与所包含类型匹配的var,并将其传入inout.

例如如果你想调用这个函数

func someFunction(obj: AutoreleasingUnsafeMutablePointer<AnyObject?>)

然后你像这样调用它:

var myObject: AnyObject? = nil
someFunction(&AnyObject)

一切都会好起来的.

我不知道你应该持有AutoreleasingUnsafeMutablePointer的任何其他情况.我不认为你应该在Swift方面手动构建一个,除非是nil.在Swift中构建具有非零内容的AutoreleasingUnsafeMutablePointer是非常困难的,因为自动释放的唯一方法是使用Unmanaged.

回应您的更新……

objc_getClassList函数签名是Swift自动C导入中的一个小故障.它错误地假设应该将Class *参数导入为AutoreleasingUnsafeMutablePointer< AnyObject?>.你真的只需要一个可以从数组中获取的UnsafeMutablePointer:

var allClasses = Array<AnyClass?>(count: Int(objc_getClassList(nil,0)),repeatedValue: nil)
allClasses.withUnsafeMutableBufferPointer { (inout bp: UnsafeMutableBufferPointer<AnyClass?>) in
    objc_getClassList(AutoreleasingUnsafeMutablePointer(bp.baseAddress),Int32(allClasses.count))
}
原文链接:https://www.f2er.com/swift/318695.html

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