如何在Objective C中动态设置UILabel的自动布局宽度和高度

UILabel *label = [[UILabel alloc] init];
label.text = @"Hello, World!";

label.translatesAutoresizingMaskIntoConstraints = NO;

// 设置宽度约束
NSLayoutConstraint *widthConstraint = [NSLayoutConstraint constraintWithItem:label attribute:NSLayoutAttributeWidth relatedBy:NSLayoutRelationEqual toItem:nil attribute:NSLayoutAttributeNotAnAttribute multiplier:1.0 constant:200];
[label addConstraint:widthConstraint];

// 设置高度约束
NSLayoutConstraint *heightConstraint = [NSLayoutConstraint constraintWithItem:label attribute:NSLayoutAttributeHeight relatedBy:NSLayoutRelationEqual toItem:nil attribute:NSLayoutAttributeNotAnAttribute multiplier:1.0 constant:50];
[label addConstraint:heightConstraint];

UIView *superview = self.view; // 父视图
[superview addSubview:label];

// 设置水平居中约束
NSLayoutConstraint *centerXConstraint = [NSLayoutConstraint constraintWithItem:label attribute:NSLayoutAttributeCenterX relatedBy:NSLayoutRelationEqual toItem:superview attribute:NSLayoutAttributeCenterX multiplier:1.0 constant:0];
[superview addConstraint:centerXConstraint];

// 设置垂直居中约束
NSLayoutConstraint *centerYConstraint = [NSLayoutConstraint constraintWithItem:label attribute:NSLayoutAttributeCenterY relatedBy:NSLayoutRelationEqual toItem:superview attribute:NSLayoutAttributeCenterY multiplier:1.0 constant:0];
[superview addConstraint:centerYConstraint];