Adding Constraints Programmatically on iOS

问题

So I'm trying to get the first and third button to take up the rest of the space of the tab bar and have the second button be a constant width. I'm getting close but I can't seem to quite get it. This is my first time adding constraints programmatically so I welcome constructive criticism. Here is the code. On the image each color is a button.

    - (void)setUpTabbarProperties {
    [self.tabBar setHidden: YES];
    [self.customTabBarView setTranslatesAutoresizingMaskIntoConstraints: NO];
    [self.firstButton setTranslatesAutoresizingMaskIntoConstraints: NO];
    [self.secondButton setTranslatesAutoresizingMaskIntoConstraints: NO];
    [self.thirdButton setTranslatesAutoresizingMaskIntoConstraints: NO];
    [self.view addSubview: self.customTabBarView];


    // This will add the constraints
    NSDictionary *viewDictionary = [NSDictionary dictionaryWithObjectsAndKeys: self.customTabBarView, @"customTabBar",
                                                                               self.firstButton, @"firstButton",
                                                                               self.secondButton, @"secondButton",
                                                                               self.thirdButton, @"thirdButton", nil];

    NSArray *horizontalConstraints = [NSLayoutConstraint constraintsWithVisualFormat: @"H:|-0-[customTabBar]-0-|"
                                                                             options: 0
                                                                             metrics: nil
                                                                               views: viewDictionary];

    NSArray *verticalConstraints = [NSLayoutConstraint constraintsWithVisualFormat: @"V:[customTabBar]-0-|"
                                                                           options: 0
                                                                           metrics: nil
                                                                             views: viewDictionary];

    NSArray *heightContraints = [NSLayoutConstraint constraintsWithVisualFormat: @"V:[customTabBar(50)]"
                                                                        options: 0
                                                                        metrics: nil
                                                                          views: viewDictionary];

    NSArray *buttonHConstraints = [NSLayoutConstraint constraintsWithVisualFormat: @"H:|-0-[firstButton]-0-[secondButton]-0-[thirdButton]-0-|"
                                                                          options: 0
                                                                          metrics: nil
                                                                            views: viewDictionary];

    NSArray *firstButtonVConstraints = [NSLayoutConstraint constraintsWithVisualFormat: @"V:|-0-[firstButton]-0-|"
                                                                         options: 0
                                                                         metrics: nil
                                                                           views: viewDictionary];

    NSArray *secondButtonVConstraints = [NSLayoutConstraint constraintsWithVisualFormat: @"V:|-0-[secondButton]-0-|"
                                                                          options: 0
                                                                          metrics: nil
                                                                            views: viewDictionary];

    NSArray *thirdButtonVConstraints = [NSLayoutConstraint constraintsWithVisualFormat: @"V:|-0-[thirdButton]-0-|"
                                                                          options: 0
                                                                          metrics: nil
                                                                            views: viewDictionary];

    NSArray *secondButtonWithConstraint = [NSLayoutConstraint constraintsWithVisualFormat: @"H:[secondButton(65)]"
                                                                                  options: 0
                                                                                  metrics: nil
                                                                                    views: viewDictionary];

    [self.view addConstraint: [NSLayoutConstraint constraintWithItem: self.secondButton
                                                           attribute: NSLayoutAttributeCenterY
                                                           relatedBy: NSLayoutRelationEqual
                                                              toItem: self.customTabBarView
                                                           attribute: NSLayoutAttributeCenterY
                                                          multiplier: 0
                                                            constant: 0]];

    [self.view addConstraints: horizontalConstraints];
    [self.view addConstraints: verticalConstraints];
    [self.view addConstraints: heightContraints];
    [self.view addConstraints: buttonHConstraints];
    [self.view addConstraints: firstButtonVConstraints];
    [self.view addConstraints: secondButtonVConstraints];
    [self.view addConstraints: thirdButtonVConstraints];
    [self.view addConstraints: secondButtonWithConstraint];
}

and here what it looks like

回答1:

I was missing the constraint. I was trying to use a different one and it didn't work but this one did.

        NSArray *firstAndThirdButtonConstraint = [NSLayoutConstraint constraintsWithVisualFormat:@"H:[firstButton(==thirdButton)]"
                                                                                     options:0
                                                                                     metrics:nil views:viewDictionary];

来源：https://stackoverflow.com/questions/26594369/adding-constraints-programmatically-on-ios