Is there any way that I can pass arguments in selector?
example: I have this method
- (void)myMethod:(NSString*)value1 setValue2:(NSString*)value2{
}
and I need to call this function through a selector passing two arguments.
[NSTimer scheduledTimerWithTimeInterval:0.1 target:self selector:@selector(/*my method*/) userInfo:nil repeats:YES];
How can I do this?
You could use the NSTimer method:
+ (NSTimer *)scheduledTimerWithTimeInterval:(NSTimeInterval)seconds
invocation:(NSInvocation *)invocation
repeats:(BOOL)repeats;
Instead, since an NSInvocation object will allow you to pass arguments; an NSInvocation object is, as the docs define it:
an Objective-C message rendered static, that is, it is an action turned into an object.
Whilst creating an NSTimer object using a selector requires the format of the method being:
- (void)timerFireMethod:(NSTimer*)theTimer
An NSInvocation allows you to set the target, the selector, and the arguments that you pass in:
SEL selector = @selector(myMethod:setValue2:);
NSMethodSignature *signature = [MyObject instanceMethodSignatureForSelector:selector];
NSInvocation *invocation = [NSInvocation invocationWithMethodSignature:signature];
[invocation setSelector:selector];
NSString *str1 = @"someString";
NSString *str2 = @"someOtherString";
//The invocation object must retain its arguments
[str1 retain];
[str2 retain];
//Set the arguments
[invocation setTarget:targetInstance];
[invocation setArgument:&str1 atIndex:2];
[invocation setArgument:&str2 atIndex:3];
[NSTimer scheduledTimerWithTimeInterval:0.1 invocation:invocation repeats:YES];
Where MyObject is the class that myMethod:setValue2: is declared and implemented on – instanceMethodSignatureForSelector: is a convenience function declared on NSObject which returns an NSMethodSignature object for you, to be passed to NSInvocation.
Also, to note, with setArgument:atIndex:, the indices for arguments to be passed to the method set as the selector start at index 2. From the docs:
Indices 0 and 1 indicate the hidden arguments self and _cmd, respectively; you should set these values directly with the setTarget: and setSelector: methods. Use indices 2 and greater for the arguments normally passed in a message.
For scheduledTimerWithTimeInterval:, the selector you pass can only have one argument. Further, its one argument must be an NSTimer * object. In other words, the selector must take the following form:
- (void)timerFireMethod:(NSTimer*)theTimer
What you could do is store the arguments in the userInfo dictionary and call the selector you want from the timer callback:
- (void)startMyTimer {
/* ... Some stuff ... */
[NSTimer scheduledTimerWithTimeInterval:0.1
target:self
selector:@selector(callMyMethod:)
userInfo:[NSDictionary dictionaryWithObjectsAndKeys:someValue,
@"value1", someOtherValue, @"value2", nil]
repeats:YES];
}
- (void)callMyMethod:(NSTimer *)theTimer {
NSString *value1 = [[theTimer userInfo] objectForKey:@"value1"];
NSString *value2 = [[theTimer userInfo] objectForKey:@"value2"];
[self myMethod:value1 setValue2:value2];
}
Looks like a job for blocks (assuming this is targeted for Snow Leopard.)
-jcr
blocks seem like an obvious answer now... but there is another idiom that was very commonplace in the classic runtime, pickle your arguments in a single object:
- (void)doMyMethod:(NSDictionary *)userInfo
{
[self myMethod: [userInfo objectForKey:@"value1"] setValue2: [userInfo objectForKey:@"value2"]];
}
- (void)myMethod:(NSString*)value1 setValue2:(NSString*)value2{
}
now you can dispatch to
[self performSelector:@selector(doMyMethod:) withObject:@{@"value1":@"value1",@"value2":@"value2"}];
@selector(myMethod:setValue2:)
Since the selector for your method isn't just called myMethod but instead myMethod:setValue2:.
Also (and I could be off base here), I believe technically you can drop the words between colons and thus also use @selector(myMethod::) but don't quote me on this unless others can confirm it.
