Setting up dependencies between channels on a custom item requires implementing ChannelUI interface .

chanUIDepend.cpp

/* 
 * If you want to create dependencies between channels on a custom item
 * such that one channel enable state depends on some other channel value
 * (on the same item) you need to implement ChannelUI interface for your item.
 */

/* This is needed to obtain the implemented custom item type.
 * (see DependencyCountIndex() method below)
 */
static CLxItemType		 	cit_self  (MY_CUSTOM_ITEM_TYPE_NAME);

class CPackage :
		public CLxImpl_Package,
		public CLxImpl_ChannelUI
{
  	// Declarations of other custom item methods go there...

  	// Declarations of ChannelUI methods.
	LxResult        cui_Enabled           (const char* channelName, ILxUnknownID msg, ILxUnknownID item, ILxUnknownID read) LXx_OVERRIDE;
	LxResult	cui_DependencyCount   (const char* channelName, unsigned* count) LXx_OVERRIDE;
	LxResult	cui_DependencyByIndex (const char* channelName, unsigned index, LXtItemType* depItemType, const char** depChannelName) LXx_OVERRIDE;
};

/* Enabled method will be called to query whether a channel of given name
 * (first argument) should be enabled or disabled.
 * Returning LXe_OK means enabled, LXe_CMD_DISABLED otherwise.
 */
	LxResult
CPackage::cui_Enabled(
	const char 		*channelName,
	ILxUnknownID 		 msg,
	ILxUnknownID		 item,
	ILxUnknownID		 read)
{
	LxResult		 result = LXe_OK;

	if (0 == strcmp (channelName, CHAN_TO_ENABLE_DISABLE_NAME)) {
		CLxUser_Item		 chanItem (item);
		CLxUser_ChannelRead	 chanRead (read);

		int otherChanVal = chanRead.IValue (chanItem, SOME_OTHER_CHAN_NAME);
		if (someValue != otherChanVal) {
			result = LXe_CMD_DISABLED;
		}
	}
	return result;
}

/* 
 * We need to set up dependencies between channels which will take care of notifications
 * and Enabled() method will be called correctly, whenever our channel needs to update
 * its enabled/disabled state.
 * Note that notifications work for setting up dependencies between channels on the same item.
 * If you need to make one of custom item's channels dependent on a channel from a different item
 * you will have to handle notifications yourself.
 */

/*
 * DependencyCount() needs to return a number of channels given channel
 * (which name is passed as first argument) will depend on.
 * In our case we make the channel dependent on one other channel.
 */
	LxResult
CPackage::cui_DependencyCount (const char* channelName, unsigned* count)
{
	if (0 == strcmp (channelName, CHAN_TO_ENABLE_DISABLE_NAME)) {
		count[0] = 1;
	}
	else {
		count[0] = 0;
	}
	return LXe_OK;
}

/*
 * This method will be called for every channel that has dependency count of at least 1
 * and it will be called for every dependency index. So if a channel depends on 2 other channels
 * this method will be called twice for a given channel, once with index 0 and once with index 1.
 * You need to return name of a channel queried channel depends on for every index.
 * You also have to set the item type properly (to your custom item type).
 */
	LxResult
CPackage::cui_DependencyByIndex (
	const char		*channelName,
	unsigned		 index,
	LXtItemType		*depItemType,
	const char	       **depChannelName)
{
	LxResult	result = LXe_OUTOFBOUNDS;
	
	if (0 == strcmp (channelName, CHAN_TO_ENABLE_DISABLE_NAME))
	{
		depItemType[0] = cit_self;
		depChannelName[0] = SOME_OTHER_CHAN_NAME;
		result = LXe_OK;
	}

	return result;
}