自学教程：C++ GetPropertyData函数代码示例

void	CAHALAudioDevice::GetStereoPanControlChannels(AudioObjectPropertyScope inScope, UInt32 inChannel, UInt32& outLeftChannel, UInt32& outRightChannel) const{	CAPropertyAddress theAddress(kAudioDevicePropertyStereoPanChannels, inScope, inChannel);	UInt32 theValue[2] = { 0, 0 };	UInt32 theSize = 2 * sizeof(UInt32);	GetPropertyData(theAddress, 0, NULL, theSize, theValue);	outLeftChannel = theValue[0];	outRightChannel = theValue[1];}

CFStringRef	CAHALAudioDevice::CopyDataDestinationNameForID(AudioObjectPropertyScope inScope, UInt32 inChannel, UInt32 inID) const{	CAPropertyAddress theAddress(kAudioDevicePropertyPlayThruDestinationNameForIDCFString, inScope, inChannel);	CFStringRef theAnswer = NULL;	AudioValueTranslation theTranslation = { &inID, sizeof(UInt32), &theAnswer, sizeof(CFStringRef) };	UInt32 theSize = sizeof(AudioValueTranslation);	GetPropertyData(theAddress, 0, NULL, theSize, &theTranslation);	return theAnswer;}

AudioObjectID	CAHALAudioSystemObject::GetAudioPlugInForBundleID(CFStringRef inUID) const{	AudioObjectID theAnswer = kAudioObjectUnknown;	AudioValueTranslation theValue = { &inUID, sizeof(CFStringRef), &theAnswer, sizeof(AudioObjectID) };	CAPropertyAddress theAddress(kAudioHardwarePropertyPlugInForBundleID);	UInt32 theSize = sizeof(AudioValueTranslation);	GetPropertyData(theAddress, 0, NULL, theSize, &theValue);	return theAnswer;}

void	CAAudioHardwareStream::GetAvailableDataSources(UInt32& ioNumberSources, UInt32* outSources) const{	UInt32 theNumberSources = std::min(GetNumberAvailableDataSources(), ioNumberSources);	UInt32 theSize = theNumberSources * sizeof(UInt32);	GetPropertyData(0, kAudioDevicePropertyDataSources, theSize, outSources);	ioNumberSources = theSize / sizeof(UInt32);	UInt32* theFirstItem = &(outSources[0]);	UInt32* theLastItem = theFirstItem + ioNumberSources;	std::sort(theFirstItem, theLastItem);}

	void Control::Show() const	{		// Make a string for the class ID		char classID[] = CA4CCToCString(mClassID);				// Get the object's name		PropertyAddress address(kCMIOObjectPropertyName, kCMIOObjectPropertyScopeGlobal, kCMIOObjectPropertyElementMaster);		CFStringRef cfname = NULL;		UInt32 dataUsed = 0;		try		{			GetPropertyData(address, 0, NULL, sizeof(CFStringRef), dataUsed, &cfname);		}		catch(...)		{			cfname = NULL;		}				// Make a C string out of the name		char name[256];		name[0] = 0;		if (cfname != NULL)		{			CFIndex length = 0;			CFRange range = { 0, CFStringGetLength(cfname) };			CFStringGetBytes(cfname, range, kCFStringEncodingUTF8, 0, false, (UInt8*)name, 255, &length);			name[length] = 0;			CFRelease(cfname);		}				// Get a string for the scope		const char* scope = NULL;		switch (GetPropertyScope())		{			case kCMIODevicePropertyScopeInput:				scope = "Input";				break;						case kCMIODevicePropertyScopeOutput:				scope = "Output";				break;						case kCMIODevicePropertyScopePlayThrough:				scope = "Play Through";				break;						case kCMIOObjectPropertyScopeGlobal:			default:				scope = "Global";				break;		};				// Print the information to the standard output		printf("CMIOObjectID:/t/t0x%lX/n/tCMIOClassID:/t'%s'/n/tName:/t/t/t%s/n/tScope:/t/t/t%s/n/tChannel:/t/t%lu/n", (long unsigned int)mObjectID, classID, name, scope, (long unsigned int)GetPropertyElement());	}

	void Device::GetStreams(CMIOObjectPropertyScope scope, UInt32& ioNumberStreams, CMIOStreamID* streamList) const	{		ioNumberStreams = std::min(GetNumberStreams(scope), ioNumberStreams);		UInt32 size = ioNumberStreams * sizeof(CMIOStreamID);		UInt32 dataUsed = 0;		GetPropertyData(PropertyAddress(kCMIODevicePropertyStreams, scope), 0, NULL, size, dataUsed, streamList);		ioNumberStreams = size / sizeof(CMIOStreamID);		CMIOStreamID* firstItem = &(streamList[0]);		CMIOStreamID* lastItem = firstItem + ioNumberStreams;		std::sort(firstItem, lastItem);	}

	bool Device::IsAlive() const	{		bool answer = HasProperty(PropertyAddress(kCMIODevicePropertyDeviceIsAlive));		if (answer)		{			UInt32 isAlive = 0;			UInt32 dataUsed = 0;			GetPropertyData(PropertyAddress(kCMIODevicePropertyDeviceIsAlive), 0, NULL, sizeof(UInt32), dataUsed, &isAlive);			answer = isAlive != 0;		}		return answer;	}

AudioDeviceID	CAAudioHardwareSystem::GetDeviceAtIndex(UInt32 inIndex){	AudioDeviceID theAnswer = 0;	UInt32 theNumberDevices = GetNumberDevices();	if((theNumberDevices > 0) && (inIndex < theNumberDevices))	{		CAAutoArrayDelete<AudioDeviceID> theDeviceList(theNumberDevices);		UInt32 theSize = theNumberDevices * sizeof(AudioDeviceID);		GetPropertyData(kAudioHardwarePropertyDevices, theSize, theDeviceList);		theAnswer = theDeviceList[inIndex];	}	return theAnswer;}

	UInt32 SelectorControl::GetItemIDForIndex(UInt32 inItemIndex) const	{		UInt32 answer = 0xFFFFFFFF;	// Default to the featuring being on		UInt32 numberOfItems = GetNumberItems();		if (numberOfItems > 0)		{			ThrowIf(inItemIndex >= numberOfItems, CAException(kCMIOHardwareIllegalOperationError), "SelectorControl::GetItemIDForIndex: index out of range");						CAAutoArrayDelete<UInt32> itemList(numberOfItems);			UInt32 size = numberOfItems * sizeof(CMIODeviceID);			UInt32 dataUsed = 0;			GetPropertyData(PropertyAddress(kCMIOSelectorControlPropertyAvailableItems),0, NULL, size, dataUsed, itemList);			answer = itemList[inItemIndex];		}		return answer;	}

	UInt32 Device::GetTotalNumberChannels(CMIOObjectPropertyScope scope) const	{		UInt32 answer = 0;		#warning Device::GetTotalNumberChannels() needs to be implemented		PropertyAddress address(kCMIODevicePropertyStreamConfiguration, scope);		UInt32 size = GetPropertyDataSize(address, 0, NULL);		CAAutoFree<CMIODeviceStreamConfiguration> streamConfiguration(size);		UInt32 dataUsed = 0;		GetPropertyData(address, 0, NULL, size, dataUsed, streamConfiguration);		for(UInt32 index = 0; index < streamConfiguration->mNumberStreams; ++index)		{			answer += streamConfiguration->mNumberChannels[index];		}		return answer;	}

AudioClassID	CAHALAudioObject::GetClassID() const{	//	set up the return value	AudioClassID theAnswer = 0;		//	set up the property address	CAPropertyAddress theAddress(kAudioObjectPropertyClass);		//	make sure the property exists	if(HasProperty(theAddress))	{		UInt32 theSize = sizeof(AudioClassID);		GetPropertyData(theAddress, 0, NULL, theSize, &theAnswer);	}		return theAnswer;}

OSStatusPA_Stream::GetProperty(UInt32 inChannel,		       AudioDevicePropertyID inPropertyID,		       UInt32 *ioPropertyDataSize,		       void *outPropertyData){	AudioObjectPropertyAddress addr;		addr.mSelector = inPropertyID;	addr.mElement = inChannel;	addr.mScope = 0;		if (!HasProperty(&addr))		return kAudioHardwareUnknownPropertyError;		return GetPropertyData(&addr, 0, NULL, ioPropertyDataSize, outPropertyData);}

	//-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------	// Control::GetVariant()	//-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------	UInt32 Control::GetVariant() const	{		// Setup the answer		CMIOObjectPropertyElement answer = GetClassID();				// Setup the property address		PropertyAddress address(kCMIOControlPropertyVariant);				// Make sure the property exists		if (HasProperty(address))		{			// Get the property data			UInt32 dataUsed = 0;			GetPropertyData(address, 0, NULL, sizeof(UInt32), dataUsed, &answer);		}				return answer;	}

	//-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------	// Control::GetPropertyScope()	//	Get the CMIOObjectPropertyScope IN THE OWNING CMIOObject that contains the control.  (Controls themselves only have kCMIOObjectPropertyScopeGlobal)	//-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------	CMIOObjectPropertyScope Control::GetPropertyScope() const	{		// Setup the answer		CMIOObjectPropertyScope answer = kCMIOObjectPropertyScopeGlobal;				// Setup the property address		PropertyAddress address(kCMIOControlPropertyScope);				// Make sure the property exists		if (HasProperty(address))		{			// Get the property data			UInt32 dataUsed = 0;			GetPropertyData(address, 0, NULL, sizeof(CMIOObjectPropertyScope), dataUsed, &answer);		}				return answer;	}

AudioDeviceID	CAAudioHardwareSystem::GetDefaultDevice(bool inIsInput, bool inIsSystem){	AudioDeviceID theAnswer = 0;	AudioHardwarePropertyID thePropertyID = 0;	if(inIsInput)	{		thePropertyID = kAudioHardwarePropertyDefaultInputDevice;	}	else if(inIsSystem)	{		thePropertyID = kAudioHardwarePropertyDefaultSystemOutputDevice;	}	else	{		thePropertyID = kAudioHardwarePropertyDefaultOutputDevice;	}	UInt32 theSize = sizeof(AudioDeviceID);	GetPropertyData(thePropertyID, theSize, &theAnswer);	return theAnswer;}