简介
Masonry 是一个非常好用的iOS开发布局框架，在使用代码布局视图时，相比原生的NSLayoutConstraint，在使用容易度和代码的可阅读程度，都优秀非常多。Masonry使用了链式语法，例如：make.left.equalTo(view.mas_bottom).offset(0);不管是使用还是阅读，都是非常易懂的。
Maosnry的GitHub连接 附上GitHub的连接，在GitHub上，开发者已经对Masonry做了非常详尽的介绍，强烈推荐阅读。
Masonry本质还是基于NSLayoutConstraint进行封装的，而且连报错的信息都优化了。
(
"<NSLayoutConstraint:0x7189ac0 V:[UILabel:0x7186980(>=5000)]>",
"<NSAutoresizingMaskLayoutConstraint:0x839ea20 h=--& v=--& V:[MASExampleDebuggingView:0x7186560(416)]>",
"<NSLayoutConstraint:0x7189c70 UILabel:0x7186980.bottom == MASExampleDebuggingView:0x7186560.bottom - 10>",
"<NSLayoutConstraint:0x7189560 V:|-(1)-[UILabel:0x7186980] (Names: '|':MASExampleDebuggingView:0x7186560 )>"
)
Will attempt to recover by breaking constraint
<NSLayoutConstraint:0x7189ac0 V:[UILabel:0x7186980(>=5000)]>
上面的报错信息是未封装前的，类似h=--& v=--& V:这样的语法提示信息，一般也是难以理解的。Masonry将其优化成如下：
(
"<NSAutoresizingMaskLayoutConstraint:0x8887740 MASExampleDebuggingView:superview.height == 416>",
"<MASLayoutConstraint:ConstantConstraint UILabel:messageLabel.height >= 5000>",
"<MASLayoutConstraint:BottomConstraint UILabel:messageLabel.bottom == MASExampleDebuggingView:superview.bottom - 10>",
"<MASLayoutConstraint:ConflictingConstraint[0] UILabel:messageLabel.top == MASExampleDebuggingView:superview.top + 1>"
)
Will attempt to recover by breaking constraint
<MASLayoutConstraint:ConstantConstraint UILabel:messageLabel.height >= 5000>
安装
基于CocoaPod进行安装
pod 'Masonry'
在引入Masonry文件时，建议加上#define MAS_SHORTHAND，这样可以简化代码，即去掉了mas_前缀。同时，也建议加上#define MAS_SHORTHAND。这样就可以将@10简化成10。
简化前的代码：
[_tableView mas_makeConstraints:^(MASConstraintMaker *make) {
make.edges.equalTo(@0);
}];
简化后的代码：
[_tableView makeConstraints:^(MASConstraintMaker *make) {
make.edges.equalTo(0);
}];
引入格式：
#define MAS_SHORTHAND_GLOBALS
#define MAS_SHORTHAND
#import "Masonry.h"
使用
实例1 简单布局
image.png
如图，简单布局两个view，如上。
UIView *view1 = [UIView new];
view1.backgroundColor = [UIColor cyanColor];
_v1 = view1;
UIView *view2 = [UIView new];
view2.backgroundColor = [UIColor greenColor];
_v2 = view2;
CGFloat screenWidth = [UIApplication sharedApplication].delegate.window.bounds.size.width;
CGFloat viewWidth = (screenWidth - 30)/2;
[self.view addSubview:view1];
[self.view addSubview:view2];
[view1 makeConstraints:^(MASConstraintMaker *make) {
make.left.equalTo(10);
make.top.equalTo(100); // 与父视图的相同方位数据设置偏移
make.height.width.equalTo(viewWidth); // 两个方位数据可以一起设置
}];
[view2 makeConstraints:^(MASConstraintMaker *make) {
make.left.equalTo(view1.mas_right).offset(10); // 这里的mas_right不能去掉前缀mas_不然会报内存泄漏
make.top.equalTo(view1).offset(0);
make.size.equalTo(viewWidth);
}];
Masonry布局的语法为：make.left.equalTo(view1.mas_right).offset(10); make表示被布局的视图，equalTo()方法入参为相对应视图的方位数据。这个入参不传入显式视图时：equalTo(0)则表示与父视图的相同方位数据对比。例如：make.left.equalTo(10);表示view1的顶部是相对于其父视图的顶部向下偏移10。
其方位数据有一下可供选择设置布局：
@property (nonatomic, strong, readonly) MASConstraint *left;
@property (nonatomic, strong, readonly) MASConstraint *top;
@property (nonatomic, strong, readonly) MASConstraint *right;
@property (nonatomic, strong, readonly) MASConstraint *bottom;
@property (nonatomic, strong, readonly) MASConstraint *leading;
@property (nonatomic, strong, readonly) MASConstraint *trailing;
@property (nonatomic, strong, readonly) MASConstraint *width;
@property (nonatomic, strong, readonly) MASConstraint *height;
@property (nonatomic, strong, readonly) MASConstraint *centerX;
@property (nonatomic, strong, readonly) MASConstraint *centerY;
@property (nonatomic, strong, readonly) MASConstraint *baseline;
@property (nonatomic, strong, readonly) MASConstraint *firstBaseline;
@property (nonatomic, strong, readonly) MASConstraint *lastBaseline;
@property (nonatomic, strong, readonly) MASConstraint *leftMargin;
@property (nonatomic, strong, readonly) MASConstraint *rightMargin;
@property (nonatomic, strong, readonly) MASConstraint *topMargin;
@property (nonatomic, strong, readonly) MASConstraint *bottomMargin;
@property (nonatomic, strong, readonly) MASConstraint *leadingMargin;
@property (nonatomic, strong, readonly) MASConstraint *trailingMargin;
@property (nonatomic, strong, readonly) MASConstraint *centerXWithinMargins;
@property (nonatomic, strong, readonly) MASConstraint *centerYWithinMargins;
@property (nonatomic, strong, readonly) MASConstraint *edges;
@property (nonatomic, strong, readonly) MASConstraint *size;
@property (nonatomic, strong, readonly) MASConstraint *center;
实例2 动态宽度进行布局
image.png
天蓝色的视图宽高设置了一样的数值，只是因为在水平方向上，两个视图的宽度不能超过屏幕的宽度，所以就将天蓝色的视图宽度压缩了。
-(void)showDemo2{
UIView *view1 = [UIView new];
view1.backgroundColor = [UIColor cyanColor];
_v1 = view1;
UIView *view2 = [UIView new];
view2.backgroundColor = [UIColor greenColor];
_v2 = view2;
CGFloat screenWidth = [UIApplication sharedApplication].delegate.window.bounds.size.width;
CGFloat viewWidth = (screenWidth - 30)/2;
[self.view addSubview:view1];
[self.view addSubview:view2];
[view1 makeConstraints:^(MASConstraintMaker *make) {
make.left.equalTo(10);
make.top.equalTo(100);
make.height.width.lessThanOrEqualTo(screenWidth);
}];
[view2 makeConstraints:^(MASConstraintMaker *make) {
make.left.equalTo(view1.mas_right).offset(10); // 这里的mas_right不能去掉前缀mas_不然会报内存泄漏
make.top.equalTo(view1).offset(0);
make.right.equalTo(-10);
make.size.equalTo(viewWidth);
}];
}
这里相较于equalTo()方法，使用了lessThanOrEqualTo()方法，于此类似还有greaterThanOrEqualTo
- (MASConstraint * (^)(id attr))mas_equalTo; // 等于
- (MASConstraint * (^)(id attr))mas_greaterThanOrEqualTo; // 大于或等于
- (MASConstraint * (^)(id attr))mas_lessThanOrEqualTo; // 小于或等于
实例3 使用优先级进行布局
image.png
同样和实例2一样，对天蓝色的视图设置的宽度为屏幕宽度，通过调低其布局约束的优先级，动态拉低天蓝色视图的宽度。
-(void)showDemo2{
UIView *view1 = [UIView new];
view1.backgroundColor = [UIColor cyanColor];
_v1 = view1;
UIView *view2 = [UIView new];
view2.backgroundColor = [UIColor greenColor];
_v2 = view2;
CGFloat screenWidth = [UIApplication sharedApplication].delegate.window.bounds.size.width;
CGFloat viewWidth = (screenWidth - 30)/2;
[self.view addSubview:view1];
[self.view addSubview:view2];
[view1 makeConstraints:^(MASConstraintMaker *make) {
make.left.equalTo(10);
make.top.equalTo(100);
make.height.equalTo(viewWidth);
make.width.equalTo(screenWidth).priorityLow();
}];
[view2 makeConstraints:^(MASConstraintMaker *make) {
make.left.equalTo(view1.mas_right).offset(10); // 这里的mas_right不能去掉前缀mas_不然会报内存泄漏
make.top.equalTo(view1).offset(0);
make.right.equalTo(-10);
make.size.equalTo(viewWidth).priorityHigh();
}];
}
priorityLow()设置低优先级。
make.size.equalTo(viewWidth).priorityHigh(); // 高优先级
make.width.equalTo(screenWidth).priorityMedium(); // 中优先级
make.width.equalTo(screenWidth).priorityLow(); // 低优先级
make.width.equalTo(screenWidth).priority(1000); // 自定义优先级， 0~1000，1000为最高
更新和删除约束
更新原有约束的常量值
[view1 updateConstraints:^(MASConstraintMaker *make) {
make.width.equalTo(viewWidth);
}];
将之前所有约束都删除之后，在重新设置新的约束
[view1 remakeConstraints:^(MASConstraintMaker *make) {
make.left.equalTo(10);
make.top.equalTo(100);
make.height.equalTo(viewWidth);
make.width.equalTo(screenWidth).priority(1000);
}];
