ios - CMVideoFormatDescriptionCreateFromH264ParameterSets抛出“UnsafePointer ”的初始化会导致指针悬空

Question

所以以前我打开了Initialization of 'UnsafePointer<Int>' results in a dangling pointer，但是mods说它是重复的。

但是我不认为这是重复的，因为在那篇文章中引用的链接不能轻易地指向解决方案。因此，我必须在3天后重新开一个。我尝试了上一篇文章中@bscothern的回答，但是出现了更多错误。

当前正在使用的代码类似于@bscothern的以下代码，但仍会抛出

无法推断通用参数“R”

var formatDesc: CMVideoFormatDescription?
func createH264FormatDescription(SPS: Array<UInt8>, PPS: Array<UInt8>) -> OSStatus {
    if formatDesc != nil { formatDesc = nil }

    let status = SPS.withUnsafeBufferPointer { SPS in
        PPS.withUnsafeBufferPointer { PPS in
            let paramSet = [SPS.baseAddress!, PPS.baseAddress!]
            let paramSizes = [SPS.count, PPS.count]
            return paramSet.withUnsafeBufferPointer { paramSet in
                paramSizes.withUnsafeBufferPointer { paramSizes in
                    CMVideoFormatDescriptionCreateFromH264ParameterSets(allocator: kCFAllocatorDefault, parameterSetCount: 2, parameterSetPointers: paramSet.baseAddress!, parameterSetSizes: paramSizes.baseAddress!, nalUnitHeaderLength: 4, formatDescriptionOut: &formatDesc)
                }
            }
        }
    }
    return status
}

来自先前帖子的原始问题:

所以我有一些代码来创建H264ParameterSets:

var formatDesc: CMVideoFormatDescription?

func createH264FormatDescription(SPS: Array<UInt8>, PPS: Array<UInt8>) -> OSStatus {
    if formatDesc != nil { formatDesc = nil }

    let paramSet = [UnsafePointer<UInt8>(SPS), UnsafePointer<UInt8>(PPS)]
    let paramPointers = UnsafePointer<UnsafePointer<UInt8>>(paramSet)
    let paramSizes = UnsafePointer<Int>([SPS.count, PPS.count])

    let status = CMVideoFormatDescriptionCreateFromH264ParameterSets(allocator: kCFAllocatorDefault, parameterSetCount: 2, parameterSetPointers: paramPointers, parameterSetSizes: paramSizes, nalUnitHeaderLength: 4, formatDescriptionOut: &formatDesc)

    return status
}

从Xcode 11.4开始，我得到了那些UnsafePointer()的警告，这似乎以前没有发生过:

Initialization of UnsafePointer<UInt8> results in a dangling pointer

Initialization of UnsafePointer<UnsafePointer<UInt8>> results in a dangling pointer

Initialization of UnsafePointer<Int> results in a dangling pointer

我不确定为什么会看到这个？以及如何删除警告？预先感谢。

Answer 1

当您发现诸如Generic parameter 'R' could not be inferred之类的错误消息时，可能有两个可能的原因。

某个地方存在与类型相关的错误，因此Swift无法在该上下文中推断出实际的R类型

该表达式比Swift可以推断

类型的复杂得多

在情况1中，您需要查找导致问题的实际错误在哪里。

在情况2中，您可以添加一些显式类型注释以帮助Swift推断类型。

请尝试这样的事情:

    var formatDesc: CMVideoFormatDescription?
    func createH264FormatDescription(SPS sps: Array<UInt8>, PPS pps: Array<UInt8>) -> OSStatus {
        if formatDesc != nil { formatDesc = nil }

        let status = sps.withUnsafeBufferPointer { spsBP->OSStatus in //<- Specify return type explicitly.
            pps.withUnsafeBufferPointer { ppsBP in
                let paramSet = [spsBP.baseAddress!, ppsBP.baseAddress!]
                let paramSizes = [spsBP.count, ppsBP.count]
                return paramSet.withUnsafeBufferPointer { paramSetBP in
                    paramSizes.withUnsafeBufferPointer { paramSizesBP in
                        CMVideoFormatDescriptionCreateFromH264ParameterSets(allocator: kCFAllocatorDefault, parameterSetCount: 2, parameterSetPointers: paramSetBP.baseAddress!, parameterSetSizes: paramSizesBP.baseAddress!, nalUnitHeaderLength: 4, formatDescriptionOut: &formatDesc)
                    }
                }
            }
        }
        return status
    }