@selector - With Multiple Arguments?
I have been using @selector
today for the first time and have not been able to work out how to do the following? How would you write the @selector
if you had more than one argument?
No arguments:
-(void)printText {
NSLog(@"Fish");
}
[self performSelector:@selector(printText) withObject:nil afterDelay:0.25];
Single argument:
-(void)printText:(NSString *)myText {
NSLog(@"Text = %@", myText);
}
[self performSelector:@selector(printText:) withObject:@"Cake" afterDelay:0.25];
Two arguments:
-(void)printText:(NSString *)myText andMore:(NSString *)extraText {
NSLog(@"Text = %@ and开发者_Go百科 %@", myText, extraText);
}
[self performSelector:@selector(printText:andMore:) withObject:@"Cake" withObject:@"Chips"];
Multiple Arguments: (i.e. more than 2)
NSInvocation
- (id)performSelector:(SEL)aSelector
withObject:(id)anObject
withObject:(id)anotherObject
From the Documentation:
This method is the same as performSelector: except that you can supply two arguments for aSelector. aSelector should identify a method that can take two arguments of type id. For methods with other argument types and return values, use NSInvocation.
so in your case you would use:
[self performSelector:@selector(printText:andMore:)
withObject:@"Cake"
withObject:@"More Cake"]
As an alternative for NSInvocation when you have more than two parameters, you can use NSObject's -methodForSelector: as in the following example:
SEL a_selector = ...
Type1 obj1 = ...
Type2 obj2 = ...
Type3 obj3 = ...
typedef void (*MethodType)(id, SEL, Type1, Type2, Type3);
MethodType methodToCall;
methodToCall = (MethodType)[target methodForSelector:a_selector];
methodToCall(target, a_selector, obj1, obj_of_type2, obj_of_type3);
I had an issue where I needed to use the afterDelay
along with multiple arguments to my @selector
method. Solution? Use a wrapper function!
Say this is the function I want to pass to @selector
:
-(void)myFunct:(NSString *)arg1 andArg:(NSString *)arg2 andYetAnotherArg:(NSString *)arg3;
Obviously, I can't even use withObject: withObject:
here, so, make a wrapper!
-(void)myFunctWrapper:(NSArray *)myArgs {
[self myFunct:[myArgs objectAtIndex:0] andArg:[myArgs objectAtIndex:1] andYetAnotherArg:[myArgs objectAtIndex:2]];
}
and use it by doing:
NSArray *argArray = [NSArray arrayWithObjects:string1,string2,string3,nil];
[self performSelector:@selector(myFunctWrapper:) withObject:argArray afterDelay:1.0];
This way I can have multiple arguments and use the selector with delay.
@selector(printText:andMore:)
[self performSelector:@selector(printText:andMore) withObject:@"Cake" withObject:@"More Cake"];
Another option is to use an even shorter syntax:
#import <objc/message.h> // objc_msgSend
...
((void (*)(id, SEL, Type1, Type2, Type3))objc_msgSend)(target, a_selector, obj1, obj_of_type2, obj_of_type3);
Elaborating on Ben-Uri's answer, which can be written way shorter.
E.g. calling the UIView
method - (CGPoint)convertPoint:(CGPoint)point toView:(UIView *)view
can
be done as follows:
SEL selector = @selector(covertPoint:toView:);
IMP method = [viewA methodForSelector:selector];
CGPoint pointInB = method(viewA, selector, pointInA, viewB);
As KennyTM pointed out, the selector syntax is
@selector(printText:andMore:)
You call it with
performSelector:withObject:withObject.
... if you need more arguments or different types, you need to use NSIvocation
Using NSInvocation as you specify you can create an NSObject category that implements
- (void)performSelector:(SEL)aSelector withObjects:(NSArray *)arguments;
Something like:
- (void)performSelector:(SEL)aSelector withObjects:(NSArray *)arguments
{
NSMethodSignature *signature = [self methodSignatureForSelector: aSelector];
NSInvocation *invocation = [NSInvocation invocationWithMethodSignature: signature];
[invocation setSelector: aSelector];
int index = 2; //
for (NSObject *argument in arguments) {
[invocation setArgument: &argument atIndex: index];
index ++;
}
[invocation invokeWithTarget: self];
}
from: iOS - How to implement a performSelector with multiple arguments and with afterDelay?
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