如何快速使用 CFDictionarySetValue？答案

【问题标题】：How to use CFDictionarySetValue in swift?如何快速使用 CFDictionarySetValue？
【发布时间】：2017-04-08 09:42:25
【问题描述】：

目前，我正在将硬件解码 Obj-C 代码转换为 Swift 版本。（Xcode 8，Swift 3）。

我不知道如何设置字典来设置屏幕上的输出选项，我也不知道如何使用它。

以下代码在 Obj-C 项目中运行良好：

// set some values of the sample buffer's attachments
CFArrayRef attachments = CMSampleBufferGetSampleAttachmentsArray(sampleBuffer, YES);
CFMutableDictionaryRef dict = (CFMutableDictionaryRef)CFArrayGetValueAtIndex(attachments, 0);
CFDictionarySetValue(dict, kCMSampleAttachmentKey_DisplayImmediately, kCFBooleanTrue);

我尝试了以下 Swift 代码，但出现了运行时错误：

// i got run-time error
let attachments = CMSampleBufferGetSampleAttachmentsArray(sampleBuffer!, true)
let dict = unsafeBitCast(attachments, to: CFMutableDictionary.self)
CFDictionarySetValue(dict, unsafeBitCast(kCMSampleAttachmentKey_DisplayImmediately, to: UnsafeRawPointer.self), unsafeBitCast(kCFBooleanTrue, to: UnsafeRawPointer.self))

把CFString转换成UnsafeRawPointer有错吗？还是用CFDictionarySetValue方法不对？

这是我的错误日志。

2016-11-24 16:50:44.458 MyApp[35288:3519253] -[__NSSingleObjectArrayI __setObject:forKey:]: unrecognized selector sent to instance 0x6000002045a0
2016-11-24 16:50:44.466 MyApp[35288:3519253] *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[__NSSingleObjectArrayI __setObject:forKey:]: unrecognized selector sent to instance 0x6000002045a0'
*** First throw call stack:
(
    0   CoreFoundation                      0x000000010b02734b __exceptionPreprocess + 171
    1   libobjc.A.dylib                     0x000000010a0e421e objc_exception_throw + 48
    2   CoreFoundation                      0x000000010b096f34 -[NSObject(NSObject) doesNotRecognizeSelector:] + 132
    3   CoreFoundation                      0x000000010afacc15 ___forwarding___ + 1013
    4   CoreFoundation                      0x000000010afac798 _CF_forwarding_prep_0 + 120
    5   MyApp                             0x000000010937ac7a _TFC14MyApp16ViewerController21receivedRawVideoFramefT5frameGSaVs5UInt8_4withVs5Int32_T_ + 4890
    6   MyApp                             0x000000010937d8e2 _TFC14MyApp16ViewerController12MainCallBackfTVs5Int3212callbackCodeS1_8argumentGSqSv_7argSizeS1__T_ + 4242
    7   MyApp                             0x000000010937daed _TToFC14MyApp16ViewerController12MainCallBackfTVs5Int3212callbackCodeS1_8argumentGSqSv_7argSizeS1__T_ + 61
    8   MyApp                            0x000000010937dd56 _TTDFC14MyApp16ViewerController12MainCallBackfTVs5Int3212callbackCodeS1_8argumentGSqSv_7argSizeS1__T_ + 70
    9   MyApp                             0x000000010937dcfe _TTWC14MyApp16ViewerControllerS_18IJCallbackProtocolS_FS1_12MainCallBackfTVs5Int3212callbackCodeS2_8argumentGSqSv_7argSizeS2__T_ + 62
    10  MyApp                             0x00000001093b22b2 _TFC14MyApp11AppDelegate19MainCallBack_StreamfTVs5Int32S1_GSqSv_S1__T_ + 258
    11  MyApp                             0x00000001093d26d3 _TFZFC14MyApp19IJStreamCoreWrapper6AttachFTSv2ipSS4portSi_T_U_FTVs5Int32S1_GSqSv_S1_GSqSv__T_ + 355
    12  MyApp                             0x00000001093d2719 _TToFZFC14MyApp19IJStreamCoreWrapper6AttachFTSv2ipSS4portSi_T_U_FTVs5Int32S1_GSqSv_S1_GSqSv__T_ + 9
    13  MyApp                             0x00000001093ee176 _ZL8CallbackPN14CStreamManager9Session_TEiPvi + 70
    14  MyApp                             0x00000001093f09d3 _Z25StreamManagerThread_VideoPv + 3155
    15  libsystem_pthread.dylib             0x000000010e494aab _pthread_body + 180
    16  libsystem_pthread.dylib             0x000000010e4949f7 _pthread_body + 0
    17  libsystem_pthread.dylib             0x000000010e494221 thread_start + 13
)
libc++abi.dylib: terminating with uncaught exception of type NSException

【问题讨论】：

显示什么是运行时错误日志可能会有所帮助。
我不确定确切的语法，但如果我没记错的话，CFDictionary 应该桥接到NSDictionary... 必须有一个简单的解决方案，涉及到 swift 关键字as。
它还桥接到 Swift 的原生 Dictionary。使用它。
Nicolas Miami 我已经使用了 ' as ' 关键字。但是，同样地，有一个错误。你是这个意思吗？ : CFDictionarySetValue(dict, kCMSampleAttachmentKey_DisplayImmediately as!UnsafeMutablePointer, kCFBooleanTrue as!UnsafeMutablePointer)
艾哈迈德 F 谢谢。我附上了错误日志

标签： swift h.264 cfstring cfdictionary

【解决方案1】：

我只能通过以下方式来解决这个问题：

let attachments = CMSampleBufferGetSampleAttachmentsArray(buf!, createIfNecessary: true)
let dict = unsafeBitCast(CFArrayGetValueAtIndex(attachments, 0), to: CFMutableDictionary.self)
CFDictionarySetValue(dict,
                     unsafeBitCast(kCMSampleAttachmentKey_DisplayImmediately, to: UnsafeRawPointer.self),
                     unsafeBitCast(kCFBooleanTrue, to: UnsafeRawPointer.self))

我尝试了@Alexander的建议，虽然编译执行了，但是底层的CFDictionary并没有发生变异，也没有达到想要的结果。

//  let attachments = CMSampleBufferGetSampleAttachmentsArray(buf!, createIfNecessary: true) as! Array<Dictionary<String, Any>>
//  var dict = attachments[0]
//  dict[kCMSampleAttachmentKey_DisplayImmediately as String] = true

【讨论】：

【解决方案2】：

在第一个代码 sn-p 中，您调用了 CFArrayGetValueAtIndex，它返回一个您传递给 CFDictionarySetValue 的字典。

在第二个代码 sn-p 中，您不调用 CFArrayGetValueAtIndex。您只需将数组传递给CFDictionarySetValue。由于数组不是字典，因此会出现致命错误。

【讨论】：

【解决方案3】：

当您将代码转换为 Swift 时，最好了解程序的语义，然后重写匹配的 Swift 代码。不要试图只是一点一点地转换语法。

CMSampleBufferGetSampleAttachmentsArray 为您返回对 CFArray 的 CFDictionary 实例的引用。将此 CFArrayRef 转换为 CFMutableDictionaryRef 的效果只是引用第一个实例。

最好只使用 Swift 的原生类型。我无法提供确切的实现，因为我不确定正在使用的类型，但这是一个开始

//TODO: give me a better name
let array = CMSampleBufferGetSampleAttachmentsArray(sampleBuffer!, true) as [[String: Bool]] //TODO:

//TODO: give me a better name
var firstDict = array[0]

firstDict[kCMSampleAttachmentKey_DisplayImmediately as String] = true

【讨论】：

感谢您的建议。我会试试的。