Moving UIView on the screen, why does this work?

Question

First of all, this code works fine, it does exactly what i need it to, however after reviewing it, i am missing something.

We have a card. When touched the card moves. When in some location it goes to that location.

-(void) touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event {
    ...
    //  Take note of the starting position and current position, both the same
    startTouchPoint = pt;
    currentTouchPoint = pt;
    ...    
}

-(void) touchesMoved:(NSSet *) touches withEvent:(UIEvent *)event {
    ...
    // As touch moves around the screen, current touch point is 
    // updated with it's new location
    currentTouchPoint = [first locationInView:self];
    ...
} 

-(void) touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event {
    ...
    // If something happens, put card in a given location
    cardCurrentlyBeingTouched.xPosition = 300;
    cardCurrentlyBeingTouched.yPosition = 150;
    ...
}

-(void) drawRect:(CGRect)rect {
   ...
   // Card moving around the screen
   cardCurrentlyBeingTouched.xPosition += (self.currentTouchPoint.x - startTouchPoint.x);
   cardCurrentlyBeingTouched.yPosition += (self.currentTouchPoint.y - startTouchPoint.y); 

   CGPoint moveToLoc = CGPointMake(cardCurrentlyBeingTouched.xPosition, cardCurrentlyBeingTouched.yPosition);

   [self addSubview:[cardCurrentlyBeingTouched uiImageViewAtPoint:moveToLoc rotated:0 withFaceImage:YES]];

   startTouchPoint.x = currentTouchPoint.x;
   startTouchPoint.y = currentTouchPoint.y;
   ...
}

So, in drawRect, (at all times) self.currentTouchPoint.x is the same as startTouchPoint.x (as Y), how in the world card's X and Y positions are changing if delta is always 0? (X and Y positions are CGPoints, when I printed them for comparison, i printed floats)

Could it be a precision issue?

This is my code, i wrote it, it works. But why? :)

Moving UIView on the screen, why does this work?

Answers (1)

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