ios - How to resize UIView by dragging from its edges?

Question

In my iPad app, I want the users to be able to resize a UIView by dragging the view from its edges. I'll be using iOS 5 SDK, so what's the cleanest approach to do this? Are there any alternatives to achieving this without dealing with touchesBegan, touchesMoved,... etc?

Answer 1

You can do this by checking the touch-start point. If it hits one of your four corners you can resize based on the distance between that touch-start point and the current-touch point. (If the touch-start point didn't hit a corner, we just move the view instead of resizing.)

Define the size of your draggable corners.

CGFloat kResizeThumbSize = 45.0f;

Add these instance variables to your class to keep track of touch state and which way we're resizing.

@interface MY_CLASS_NAME : UIView {
    BOOL isResizingLR;
    BOOL isResizingUL;
    BOOL isResizingUR;
    BOOL isResizingLL;
    CGPoint touchStart;
}

Handle the touch start / change events.

- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event {
    UITouch *touch = [[event allTouches] anyObject];
    touchStart = [[touches anyObject] locationInView:self];
    isResizingLR = (self.bounds.size.width - touchStart.x < kResizeThumbSize && self.bounds.size.height - touchStart.y < kResizeThumbSize);
    isResizingUL = (touchStart.x <kResizeThumbSize && touchStart.y <kResizeThumbSize);
    isResizingUR = (self.bounds.size.width-touchStart.x < kResizeThumbSize && touchStart.y<kResizeThumbSize);
    isResizingLL = (touchStart.x <kResizeThumbSize && self.bounds.size.height -touchStart.y <kResizeThumbSize);
}

 - (void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event {
    CGPoint touchPoint = [[touches anyObject] locationInView:self];
    CGPoint previous = [[touches anyObject] previousLocationInView:self];

    CGFloat deltaWidth = touchPoint.x - previous.x;
    CGFloat deltaHeight = touchPoint.y - previous.y;

    // get the frame values so we can calculate changes below
    CGFloat x = self.frame.origin.x;
    CGFloat y = self.frame.origin.y;
    CGFloat width = self.frame.size.width;
    CGFloat height = self.frame.size.height;

    if (isResizingLR) {
        self.frame = CGRectMake(x, y, touchPoint.x+deltaWidth, touchPoint.y+deltaWidth);
    } else if (isResizingUL) {
        self.frame = CGRectMake(x+deltaWidth, y+deltaHeight, width-deltaWidth, height-deltaHeight);
    } else if (isResizingUR) {
        self.frame = CGRectMake(x, y+deltaHeight, width+deltaWidth, height-deltaHeight);      
    } else if (isResizingLL) {
        self.frame = CGRectMake(x+deltaWidth, y, width-deltaWidth, height+deltaHeight);   
    } else {
        // not dragging from a corner -- move the view
        self.center = CGPointMake(self.center.x + touchPoint.x - touchStart.x,
            self.center.y + touchPoint.y - touchStart.y);
    }
}