如何在 swift 中使用 CFDictionarySetValue？

Question

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，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转成UnsafeRawPointer是不是错了？或者使用 CFDictionarySetValue 方法是错误的吗？

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

Answer 1

在第一个代码片段中，您调用了 CFArrayGetValueAtIndex，其中 returns 您传递给 CFDictionarySetValue 的字典。

在第二个代码片段中，您没有调用 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。

Answer 2

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 returns 您引用了 CFArray 个 CFDictionary 个实例。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

Answer 3

我只能通过以下方式实现此功能：

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，虽然它编译并执行了，但底层的 CFDictionary 没有发生变化，没有达到预期的结果。

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

如何在 swift 中使用 CFDictionarySetValue？

How to use CFDictionarySetValue in swift?

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