ios – 如何使用AutoLayout将UIButtons放置在水平线(包装,左对齐

(我的猜测是,直接设置每个按钮的框架会导致比使用NSLayoutConstraints更可读的代码)

NSArray *texts = @[ @"A",@"Short",@"Button",@"Longer Button",@"Very Long Button",@"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<texts.count; i++) {
    UIButton *button = [UIButton buttonWithType:UIButtonTypeRoundedRect];
    [button setTitle:[texts objectAtIndex:i] forState:UIControlStateNormal];
    [button sizeToFit];
    button.translatesAutoresizingMaskIntoConstraints = NO;

    [self.view addSubview:button];

    // check if first button or button would exceed maxWidth
    if ((i == 0) || (runningWidth + button.frame.size.width > 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];
}