How to repeatedly perform an action when a button

Question

I've got four simple methods, four buttons and one object.

- (IBAction)left:(id)sender{
    object.center = CGPointMake(object.center.x - 5, object.center.y);
}

- (IBAction)right:(id)sender{
    object.center = CGPointMake(object.center.x + 5, object.center.y);
}
- (IBAction)down:(id)sender{
    object.center = CGPointMake(object.center.x, object.center.y + 5);
}
- (IBAction)up:(id)sender{
    object.center = CGPointMake(object.center.x, object.center.y - 5);
}

When I press a button, the method is executed once. When the button is pressed continuously it's the same. What do I have to do so that when I press the button continuously my object keep moving to the left?

Answer 1

As @Maudicus said, you probably need to do something with NSTimers to get a continuous button press triggering. The example I'm going to use is moving an object on screen (since you want to do that anyway). I've used graded moving because I have no idea whether you are writing a grid-based game and so need exactly 5 pixels of movement. Just cut out all of the stepSize code and set it to 5 if that's what you do.

1. Write a timer callback function which checks whether a BOOL is set and if so keeps triggering itself:

   - (void)moveObjectLeft:(NSTimer *)timer
   {
       // check the total move offset and/or the X location of the object here
       // if the object can't be moved further left then invalidate the timer
       // you don't need to check whether the button is still being pressed
       //[timer invalidate];
       //return;
   
       // the object moves gradually faster as you hold the button down for longer
       NSNumber *moveOffset = (NSNumber *)[timer userInfo];
       NSUInteger stepSize = 1;
       if(moveOffset >= 40)
           stepSize = 10;
       else if(moveOffset >= 15)
           stepSize = 5;
       else if(moveOffset >= 5)
           stepSize = 2;
   
       // move the object
       object.center = CGPointMake(object.center.x - stepSize, object.center.y);
   
       // store the new total move offset for this press
       moveOffset += stepSize;
       [timer setUserInfo:moveOffset];
   }
   

2. Create a timer property in the current classes .h:

   @property (nonatomic, retain) NSTimer *moveTimer;
   

3. Synthesize it in your .m:

   @synthesize moveTimer;
   

4. Create your timer object when the button is pressed. Either do this in touchesBegan:withEvent: and check it's a Touch Down event, or connect the Touch Down event in Interface Builder to an IBAction method.

   NSNumber *moveOffset = [NSNumber numberWithUnsignedInt:0];
   self.moveTimer =
       [NSTimer
        scheduledTimerWithTimeInterval:0.2
        target:self
        selector:@selector(moveObject:)
        userInfo:moveOffset
        repeats:YES];
   

5. When the button is released (using one of the above methods again, touchesEnded:withEvent: for a Touch Up Inside or probably even a Touch Up Outside, or another IBAction on both of those events), invalidate the timer externally:

   [self.moveTimer invalidate];
   self.moveTimer = nil;
   

Answer 2

When a button gives its mousedown event, start moving. When the button gives its mouseup event, stop moving.

Be careful; this can act funny if multiple buttons can be pressed at the same time.

Answer 3

I think you need to schedule a timer and repeat a method that checks the button states.

// assume timer is set up to test button states, triggering controlLoop every x seconds

-(void)controlsLoop
{
    if (leftButton.state == UIControlStateSelected || leftButton.state == UIControlStateHighlighted)  {

    }
}

I have never done this before so have fun playing around with it. I usually achieve controls like you want in Cocos2d,

It might be better to implement these methods

- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event
- (void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event
- (void)touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event
- (void)touchesCancelled:(NSSet *)touches withEvent:(UIEvent *)event

to set which direction you want to move the object, and still have a timer triggering the actual movement.