UIControl - changing assigned selectors: addTarget & removeTarget

问题

I'm using 10 buttons in my interface and need, from time to time, to change the button's selector.

Am I required to use:

-(void)removeTarget:(id)target action:(SEL)action forControlEvents:(UIControlEvents)controlEvents 

before I change the selector or can I just use:

-(void)addTarget:(id)target action:(SEL)action forControlEvents:(UIControlEvents)controlEvents 

I'm concerned that if I change the selector using the addTarget: method sans the removeTarget: method that I'll essentially "stack up" selectors for my UIButton to fire when it is pressed.

回答1:

Yes you should always remove the previously add target before assigning the new target to the button. Like this---

UIButton *btn = [UIButton buttonWithType:UIButtonTypeRoundedRect];
    [btn setFrame:CGRectMake(50, 50, 200, 50)];

    [btn setTag:101];
    [btn addTarget:self action:@selector(method1) forControlEvents:UIControlEventTouchUpInside];
    [self.view addSubview:btn];


    btn = (UIButton *)[self.view viewWithTag:101];
    [btn removeTarget:self action:@selector(method1) forControlEvents:UIControlEventTouchUpInside];
    [btn addTarget:self action:@selector(method2) forControlEvents:UIControlEventTouchUpInside];

now if you do this

btn = (UIButton *)[self.view viewWithTag:101];
        [btn addTarget:self action:@selector(method2) forControlEvents:UIControlEventTouchUpInside];

then both the methods method1 and method2 will be called.

Hope this helps.

回答2:

Yes, you will need to remove the old target/action or both the old and new actions will be performed.

来源：https://stackoverflow.com/questions/1978751/uicontrol-changing-assigned-selectors-addtarget-removetarget