关于约束

关于约束

首先 Button.translatesAutoresizingMaskIntoConstraints = NO;
创建完按钮再添加约束
NSLayoutConstraint *constraint = [NSLayoutConstraint constraintWithItem:firstButton attribute:NSLayoutAttributeLeading relatedBy:NSLayoutRelationEqualtoItem:self.view attribute:NSLayoutAttributeLeading multiplier:1.0f constant:20.f];
[self.view addConstraint:constraint];

总结一句话：始终遵循下面的规律：

• viewA.attribute = viewB.attributs*multiplier + constant