Objective-C: passing a string parameter to tapgesture #selector - ios

Question

What I am trying to achieve is this: when I tap an specific UIImageView, the UITapGesture will pass a string into the tap method.
My code follows below: Imagine I have an UIImageView object there already, and when I tap this image, it will make a phone call,
UITapGestureRecognizer *tapFirstGuy = [[UITapGestureRecognizer alloc] initWithTarget:self action:#selector(makeCallToThisPerson:#"1234567")];
[imageViewOne addGestureRecognizer:tapFirstGuy];
- (void)makeCallToThisPerson:(NSString *)phoneNumber
{
NSString *phoneNum = [NSString stringWithFormat:#"tel:%#", phoneNumber];
[[UIApplication sharedApplication] openURL:[NSURL URLWithString:phoneNum]];
}
However, I am getting the following compile error: #selector(makeCallToThisPerson:#"1234567");
I cannot figure what is happening. Why can't I pass string to the private method?

Answer 1

One more way you can try writing subclass of UITapGestureRecognizer like that below:-
#interface customTapGestureRecognizer : UITapGestureRecognizer
#property (nonatomic, strong) NSString * phoneNumber;
#end
// customTapGestureRecognizer.m
#implementation customTapGestureRecognizer
#end
// =====================
....
customTapGestureRecognizer *singleTap = [[customTapGestureRecognizer alloc] initWithTarget:self action:#selector(makeCallToThisPerson:)];
singleTap.phoneNumber = #"1234567";
-(void) makeCallToThisPerson:(UITapGestureRecognizer *)tapRecognizer {
customTapGestureRecognizer *tap = (customTapGestureRecognizer *)tapRecognizer;
NSLog(#"phoneNumber : %#", tap.phoneNumber);
}
Note:- The advantages of writing subclass is that you can pass more number of data easily in your UITapGestureRecognizer.

Answer 2

This is wrong, It's not a valid selector.
UITapGestureRecognizer *tapFirstGuy = [[UITapGestureRecognizer alloc] initWithTarget:self action:#selector(makeCallToThisPerson:#"1234567")];
You need to change to this:
UITapGestureRecognizer *tapFirstGuy = [[UITapGestureRecognizer alloc] initWithTarget:self action:#selector(makeCallToThisPerson:)];
In your methods the parameter will be the tapGesture, that's it:
- (void)makeCallToThisPerson:(UITapGestureRecognizer *)tapGesture
You can do several things, in order to pas a parameter:
1.- Use de tag of the imageView, the tapGesture knows the view than it´s attached you can use the tag view:
UITapGestureRecognizer *tapFirstGuy = [[UITapGestureRecognizer alloc] initWithTarget:self action:#selector(makeCallToThisPerson:)];
imageViewOne.tag = 1234567
[imageViewOne addGestureRecognizer:tapFirstGuy];
- (void)makeCallToThisPerson:(UITapGestureRecognizer *)tapGesture
{
NSString *phoneNum = [NSString stringWithFormat:#"tel:%ld",tapGesture.view.tag];
[[UIApplication sharedApplication] openURL:[NSURL URLWithString:phoneNum]];
}
Other option, subclassing in order to attach a NSString to imageView as a new property.

Answer 3

The action should be just the selector for a method whose signature must be "method that takes a single id parameter and returns void". The id parameter will (typically) be the object sending the message.
The target (the object the action is sent to) can use the sender parameter to extract additional information if needed, but that additional information needs to be asked for. It isn't supplied gratis.
That is, your ImageView subclass might have methods like:
- (void)setPhoneNumber:(NSString *)phoneNumber; // set a phoneNumber property
- (void)prepareToBeTapped
{
UITapGestureRecognizer *tapFirstGuy = [[UITapGestureRecognizer alloc]
initWithTarget:self action:#selector(makeCallToThisPerson:)];
[self addGestureRecognizer:tapFirstGuy];
}
- (void)makeCallToThisPerson:(id)sender
{
NSString *phoneURL = [NSString stringWithFormat:#"tel:%#", phoneNumber];
[[UIApplication sharedApplication] openURL:[NSURL URLWithString:phoneURL]];
}
That is, it's not the action nor even the UITapGestureRecognizer that knows the phone number. The target must know (or be able to obtain) the phone number some other way, perhaps carrying it as a settable property.

Answer 4

#OnikIV's suggestion of using the tag would work fine if the value you want to pass is an integer.
If you want to pass a string however it won't work so well.
You could set the tag to a unique value, then in the gesture recoginizer's action method, convert the tag value to an NSNumber and use it as a key to look up a value in a dictionary of phone numbers.
Another other option is to use associative storage to attach strings to your image views. Associative Storage is a technique that lets you attach key/value pairs to any arbitrary NSObject.
I have a sample project called AssociativeStorageDemo on github that shows how to use it.