How to use AutoLayout to position UIButtons in horizontal lines (wrapping, left aligned)?

Question

I need to create a couple of UIButtons with various widths programmatically in my app (iOS 6.0 and above).

I want to display the buttons in a \"wrap around\" style:

Answer 1

My current solution looks like this: No AutoLayout, but manually setting the correct constraints for each case (first button, leftmost button in a new line, any other button).

(My guess is that setting the frame for each button directly would result in more readable code than using NSLayoutConstraints, anyway)

NSArray *texts = @[ @"A", @"Short", @"Button", @"Longer Button", @"Very Long Button", @"Short", @"More Button", @"Any Key"];

int indexOfLeftmostButtonOnCurrentLine = 0;
NSMutableArray *buttons = [[NSMutableArray alloc] init];
float runningWidth = 0.0f;
float maxWidth = 300.0f;
float horizontalSpaceBetweenButtons = 10.0f;
float verticalSpaceBetweenButtons = 10.0f;

for (int i=0; i maxWidth)) {
        // wrap around into next line
        runningWidth = button.frame.size.width;

        if (i== 0) {
            // first button (top left)
            // horizontal position: same as previous leftmost button (on line above)
            NSLayoutConstraint *horizontalConstraint = [NSLayoutConstraint constraintWithItem:button attribute:NSLayoutAttributeLeft relatedBy:NSLayoutRelationEqual toItem:self.view attribute:NSLayoutAttributeLeft multiplier:1.0f constant:horizontalSpaceBetweenButtons];
            [self.view addConstraint:horizontalConstraint];

            // vertical position:
            NSLayoutConstraint *verticalConstraint = [NSLayoutConstraint constraintWithItem:button attribute:NSLayoutAttributeTop relatedBy:NSLayoutRelationEqual toItem:self.view attribute:NSLayoutAttributeTop              multiplier:1.0f constant:verticalSpaceBetweenButtons];
            [self.view addConstraint:verticalConstraint];


        } else {
            // put it in new line
            UIButton *previousLeftmostButton = [buttons objectAtIndex:indexOfLeftmostButtonOnCurrentLine];

            // horizontal position: same as previous leftmost button (on line above)
            NSLayoutConstraint *horizontalConstraint = [NSLayoutConstraint constraintWithItem:button attribute:NSLayoutAttributeLeft relatedBy:NSLayoutRelationEqual toItem:previousLeftmostButton attribute:NSLayoutAttributeLeft multiplier:1.0f constant:0.0f];
            [self.view addConstraint:horizontalConstraint];

            // vertical position:
            NSLayoutConstraint *verticalConstraint = [NSLayoutConstraint constraintWithItem:button attribute:NSLayoutAttributeTop relatedBy:NSLayoutRelationEqual toItem:previousLeftmostButton attribute:NSLayoutAttributeBottom multiplier:1.0f constant:verticalSpaceBetweenButtons];
            [self.view addConstraint:verticalConstraint];

            indexOfLeftmostButtonOnCurrentLine = i;
        }
    } else {
        // put it right from previous buttom
        runningWidth += button.frame.size.width + horizontalSpaceBetweenButtons;

        UIButton *previousButton = [buttons objectAtIndex:(i-1)];

        // horizontal position: right from previous button
        NSLayoutConstraint *horizontalConstraint = [NSLayoutConstraint constraintWithItem:button attribute:NSLayoutAttributeLeft relatedBy:NSLayoutRelationEqual toItem:previousButton attribute:NSLayoutAttributeRight multiplier:1.0f constant:horizontalSpaceBetweenButtons];
        [self.view addConstraint:horizontalConstraint];

        // vertical position same as previous button
        NSLayoutConstraint *verticalConstraint = [NSLayoutConstraint constraintWithItem:button attribute:NSLayoutAttributeTop relatedBy:NSLayoutRelationEqual toItem:previousButton attribute:NSLayoutAttributeTop multiplier:1.0f constant:0.0f];
        [self.view addConstraint:verticalConstraint];
    }

    [buttons addObject:button];
}