ios - 如何以编程方式为不同数量的 UIView 设置约束

Question

我是自动布局约束的新手。在我的应用程序中，一行有 3 个按钮。现在我想以编程方式设置约束，如下图所示:

如果有，则按钮水平居中显示。如果启用了两个按钮，则第二行显示在与三个图像相同的图像中。

Answer 1

我的做法是一开始就把所有按钮centerX设置到superview的centerX

IBOutletCollection(UIButton) NSArray *allButtons;
//3 buttons' references
IBOutletCollection(NSLayoutConstraint) NSArray *allButtonCenterConstraints;
//buttons' centerX constraints' references

然后如果在 viewDidAppear:

int t = arc4random() %3;// one of the 3 cases you will need


    if (t == 0) {//if you want all 3 buttons appears
        //all buttons shown
        NSLayoutConstraint *c1 = allButtonCenterConstraints[0];//first button's centerX reference.
        NSLayoutConstraint *c2 = allButtonCenterConstraints[2];//third button's centerX reference.

        c1.constant = -self.view.frame.size.width*0.25;//push left
        c2.constant = +self.view.frame.size.width*0.25;//push right
    }
    else if (t == 1)
    {
        //two buttons shown;
        [allButtons[0] setHidden:YES];// close the one you dont need
        NSLayoutConstraint *c1 = allButtonCenterConstraints[1];
        NSLayoutConstraint *c2 = allButtonCenterConstraints[2];

        c1.constant = -self.view.frame.size.width*0.125;
        c2.constant = +self.view.frame.size.width*0.125;

    }
    else
    {
        //close 2 buttons
        [allButtons[0] setHidden:YES];
        [allButtons[1] setHidden:YES];
    }
    [self.view layoutIfNeeded];

如果你需要的东西取决于按钮的宽度，你可以根据按钮的宽度设置常量。