How to pass a variable to a UIButton action

Question

I want to pass a variable to a UIButton action, for example

NSString *string=@"one";
[downbutton addTarget:self action:@selector(action1:string)
     forControlEvents:UIControlEventTouchUpInside];

and my action function is like:

-(void) action1:(NSString *)string{
}

However, it returns a syntax error. How to pass a variable to a UIButton action?

Answer 1

Change it to read:

[downbutton addTarget:self action:@selector(action1:) forControlEvents:UIControlEventTouchUpInside];

I don't know about the Iphone SDK, but the target of a button action probably receives an id (usually named sender).

- (void) buttonPress:(id)sender;

Within the method call, sender should be the button in your case, allowing you to read properties such as it's name, tag, etc.

Answer 2

If you need to distinguish between multiple buttons, then you could mark your buttons with tags like this:

[downbutton addTarget:self action:@selector(buttonPress:) forControlEvents:UIControlEventTouchUpInside];
downButton.tag = 15;

In your action delegate method you can then handle each button according to its previously set tag:

(void) buttonPress:(id)sender {
    NSInteger tid = ((UIControl *) sender).tag;
    if (tid == 15) {
        // deal with downButton event here ..
    }
    //...
}

UPDATE: sender.tag should be a NSInteger instead of a NSInteger *

Answer 3

You can use associative references to add arbitrary data to your UIButton:

static char myDataKey;
...
UIButton *myButton = ...
NSString *myData = @"This could be any object type";
objc_setAssociatedObject (myButton, &myDataKey, myData, 
  OBJC_ASSOCIATION_RETAIN);

For the policy field (OBJC_ASSOCIATION_RETAIN) specify the appropriate policy for your case. On the action delegate method:

(void) buttonPress:(id)sender {
  NSString *myData =
    (NSString *)objc_getAssociatedObject(sender, &myDataKey);
  ...
}