Question

I’m designing an app that involves linear graphs. What I have right now is a line with three dots: one in the center for moving the whole line, and the other two, lower and higher on the line, for rotating it. The problem that I have is figuring out how to rotate the other two dots when the user touches on either of them.

I haven’t actually done much with the rotation dots yet, but here’s my code so far:

- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event
{
    UITouch* touch = [touches anyObject];
    CGPoint point = [touch locationInView:graph];
    if (CGRectContainsPoint(moveDot.frame, point)) {
        moveDotIsTouched = YES;
    }
    if (CGRectContainsPoint(rotateDot1.frame, point)) {
        rotateDot1IsTouched = YES;
    }
    if (CGRectContainsPoint(rotateDot2.frame, point)) {
        rotateDot2IsTouched = YES;
    }
}

- (void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event
{
    UITouch* touch = [touches anyObject];
    CGPoint point = [touch locationInView:graph];
    if (moveDotIsTouched) {
        if ((point.y > 0) && (point.y < 704))
        {
            if (point.y < 64) {rotateDot1.hidden = YES;}
            else {rotateDot1.hidden = NO;}
            if (point.y > 640) {rotateDot2.hidden = YES;}
            else {rotateDot2.hidden = NO;}
            moveDot.center = CGPointMake(moveDot.center.x, point.y);
            rotateDot1.center = CGPointMake(moveDot.center.x+64, moveDot.center.y-64);
            rotateDot2.center = CGPointMake(moveDot.center.x-64, moveDot.center.y+64);
            graph.base = -(point.y)/32 + 11;
            if (graph.base < 0) {[functionField setText:[NSString stringWithFormat:@"y = %.2fx %.2f", graph.slope, graph.base]];}
            else if (graph.base > 0) {[functionField setText:[NSString stringWithFormat:@"y = %.2fx + %.2f", graph.slope, graph.base]];}
            else {[functionField setText:[NSString stringWithFormat:@"y = %.2fx", graph.slope]];}
            [yintField setText:[NSString stringWithFormat:@"%.2f", graph.base]];
            [self changeTable];
        }
    }
    [graph setNeedsDisplay];
}

The numbers involving the positioning of the dots are measured in pixels. The only way I can really think of rotating the outside dots is by calculating a radius and making sure the dots are within the radius, but I’m wondering if there isn’t something simpler than that. Does anyone know a simple way to move a UIImageView in a circle?

Answer 1

KTOneFingerRotationGestureRecognizer is a custom UIGestureRecognizer for doing one finger rotations in iOS apps. It tracks finger movement around a central point. I don’t know if this is exactly what you want, but it may point you in the right direction.