BMAutoLayout

基于 Objective-C 的锚点布局

由于 Masonry 的作者不再维护 OC 版本的自动布局库，而 Apple 早已从繁杂的布局接口更换为基于 NSLayoutAnchor 的布局。由于工作需求，我仿照 Masonry 撰写了一套与 Masonry API 相同的代码，其内部核心代码使用 NSLayoutAnchor 布局。本代码支持 iOS 9.0 及以上版本。
注意 safeAreaLayoutGuide 是在 iOS 11.0 之后推出的，因此如果代码中使用了 safeAreaLayoutGuide，则要确保当前系统版本大于或等于 iOS 11.0。

安装

pod 'BMAutoLayout'

调用示例：

#import <BMAutoLayout/BMAutoLayout.h>

self.topView = [[UIView alloc] initWithFrame:CGRectZero];
self.topInnerView = [[UIView alloc] initWithFrame:CGRectZero];
self.bottomView = [[UIView alloc] initWithFrame:CGRectZero];
self.bottomInnerView = [[UIView alloc] initWithFrame:CGRectZero];

// Set background colors
UIColor *blueColor = [UIColor colorWithRed:0.663 green:0.796 blue:0.996 alpha:1];
[self.topView setBackgroundColor:blueColor];

UIColor *lightGreenColor = [UIColor colorWithRed:0.784 green:0.992 blue:0.851 alpha:1];
[self.topInnerView setBackgroundColor:lightGreenColor];

UIColor *pinkColor = [UIColor colorWithRed:0.992 green:0.804 blue:0.941 alpha:1];
[self.bottomView setBackgroundColor:pinkColor];

UIColor *darkGreenColor = [UIColor colorWithRed:0.443 green:0.780 blue:0.337 alpha:1];
[self.bottomInnerView setBackgroundColor:darkGreenColor];

// Layout top and bottom views to each take up half of the window
[self addSubview:self.topView];

[self.topView bm_makeConstraints:^(BMConstraintMaker *make) {
    make.left.right.top.equalTo(self);
}];

[self addSubview:self.bottomView];
[self.bottomView bm_makeConstraints:^(BMConstraintMaker *make) {
    make.left.right.bottom.equalTo(self);
    make.top.equalTo(self.topView.bottomAnchor);
    make.height.equalTo(self.topView);
}];

// Inner views are configured for aspect fit with ratio of 3:1
[self.topView addSubview:self.topInnerView];

[self.topInnerView bm_makeConstraints:^(BMConstraintMaker *make) {
    make.width.equalTo(self.topInnerView.heightAnchor).multipliedBy(3);
    make.width.height.lessThanOrEqualTo(self.topView);
    make.width.height.equalTo(self.topView).priorityLow();
    make.center.equalTo(self.topView);
}];

[self.bottomView addSubview:self.bottomInnerView];
[self.bottomInnerView bm_makeConstraints:^(BMConstraintMaker *make) {
    make.height.equalTo(self.bottomInnerView.widthAnchor).multipliedBy(3);
    make.width.height.lessThanOrEqualTo(self.bottomView);
    make.width.height.equalTo(self.bottomView).priorityLow();
    make.center.equalTo(self.bottomView);
}];