Scaling UITextView And Font Size Change

Question

When I add UIPinchGestureRecognizer to my UITextView:

UIPinchGestureRecognizer *pinchRecognizer = [[UIPinchGestureRecognizer alloc] initWithTarget:self action:@selector(didScaleView:)];
[pinchRecognizer setDelegate:self];
[textView addGestureRecognizer:pinchRecognizer];

the view increases in size when scaling it up and all text inside becomes increased also. However, when I print UIFont or attributedText properties:

NSLog(@"in didScaleView font %@",view.font);

the font size remains always the same (for example, 22px). Here is the scaling part:

-(void)didScaleView:(id)sender{

[self.view bringSubviewToFront:[(UIPinchGestureRecognizer*)sender view]];

if([(UIPinchGestureRecognizer*)sender state] == UIGestureRecognizerStateEnded) {

    lastScale = 1.0;
    return;
}

CGFloat scale = 1.0 - (lastScale - [(UIPinchGestureRecognizer*)sender scale]);

CGAffineTransform currentTransform = [(UIPinchGestureRecognizer*)sender view].transform;
CGAffineTransform newTransform = CGAffineTransformScale(currentTransform, scale, scale);

[[(UIPinchGestureRecognizer*)sender view] setTransform:newTransform];

lastScale = [(UIPinchGestureRecognizer*)sender scale];

}

So, what controls the font size change (ie how does it change) and how to keep it unchanged when scaling the UITextView?

Answer 1

The Affine Transform scaling factor is applied to text like anything else. So the onscreen text size should be the nominal textsize times the scaling factor. Ie, a 22px typeface zoomed by pinching to 1.25 scale would be 22 * 1.25 = 27.5px typeface.

Therefore, to keep the text size unchanged, you'd have to do the reverse: In your pinch recognizer, redraw the text in a typesize that is the nominal size DIVIDED by the scaling factor. Hence, draw 22px type at 22/1.25 = (about) 18px fontsize - which when scaled would be close to your original 22px size.

Clearly rounding is a potential issue, and you need to ensure the views of the text objects actually get redrawn. Does this help?