advertising tx power level in iOS - ios

Question

I am currently programming the peripheral side of an app. I want to advertise the tx power level, but all i have found as far as tx documentation is:
CB_EXTERN NSString * const CBAdvertisementDataTxPowerLevelKey; // A NSNumber
I have tried to implement this in the following way:
/** Start advertising
*/
- (IBAction)switchChanged:(id)sender
{
[self.peripheralManager startAdvertising:#{ CBAdvertisementDataServiceUUIDsKey : #[[CBUUID UUIDWithString:TRANSFER_SERVICE_UUID]] }];
[self.peripheralManager startAdvertising: CBAdvertisementDataTxPowerLevelKey];
}
#end
I keep getting a warning on my last line of code saying "Incompatible pointer types sending 'NSString*' to parameter of type 'NSDictionary*'. I understand that my TxPowerLevelKey is a NSString, but what is NSDictionary referring to?

Answer 1

Other answers have addressed how your dictionary is defined, however, you were looking for a higher level issue; How to transmit the txPower level from an iOS device.
The answer is that currently you can't. After you fixed your code, it compiled and ran, but CoreBluetooth is simply ignoring that key.
As stated by the documentation:
An optional dictionary containing the data you want to advertise. The
possible keys of an advertisementData dictionary are detailed in
CBCentralManagerDelegate Protocol Reference. That said, only two of
the keys are supported for peripheral manager objects:
CBAdvertisementDataLocalNameKey and
CBAdvertisementDataServiceUUIDsKey.
Hope that helps

Answer 2

In Objective-C, #{} is shorthand for [NSDictionary dictionaryWithObjectsAndKeys:(id), ..., nil]. The warning indicates the -[PeripheralManager startAdvertising] method is expecting an NSDictionary. Try wrapping the key in a dictionary with a Boolean True value (represented as an NSNumber object with #(YES)):
[self.peripheralManager startAdvertising:#{ CBAdvertisementDataTxPowerLevelKey : #(YES)}];

Answer 3

As you don't seem to know what an NSDictionary* object is please see the Apple Documentation for NSDictionary.
But to answer your question the warning
Incompatible pointer types sending 'NSString*' to parameter of type 'NSDictionary*
which is referring to
[self.peripheralManager startAdvertising: CBAdvertisementDataTxPowerLevelKey];
Is because startAdvertising: will be declared something like
- (void)startAdvertising:(NSDictionary *)start;
So it is expecting you to pass in an NSDictionary* object whereas at the moment you are passing in an NSString* object.
You can resolve this in one of two ways. The first way would be to use the short hand way like you have already done here
[self.peripheralManager startAdvertising:#{ CBAdvertisementDataServiceUUIDsKey : #[[CBUUID UUIDWithString:TRANSFER_SERVICE_UUID]] }];
Notice that the shorthand version of an NSDictionary* object starts at #{ and ends at } so the to declare an NSDictionary* object this way it would be something like #{ Key : Object } so for you it would be #{ CBAdvertisementDataTxPowerLevelKey : #(YES) }
The second way of declaring this would be to do it as I would think of the normal way like :
[NSDictionary dictionaryWithObjectsAndKeys:#(YES), CBAdvertisementDataTxPowerLevelKey, nil]
if you have any questions please just ask.