Masonry是一款輕量級(jí)的布局框架，采用方便的鏈?zhǔn)秸Z(yǔ)法，可以更方便的幫助我們使用純代碼布局
下載地址：https://github.com/SnapKit/Masonry
導(dǎo)入方式：#import "Masonry.h"
約束的三種方法
//添加新約束
- (NSArray *)mas_makeConstraints:(void(NS_NOESCAPE ^)(MASConstraintMaker *make))block;
//更新約束，會(huì)覆蓋之前的約束
- (NSArray *)mas_updateConstraints:(void(NS_NOESCAPE ^)(MASConstraintMaker *make))block;
//完全移除舊約束，添加新約束
- (NSArray *)mas_remakeConstraints:(void(NS_NOESCAPE ^)(MASConstraintMaker *make))block;
約束的基本屬性
@property (nonatomic, strong, readonly) MASConstraint *left;
@property (nonatomic, strong, readonly) MASConstraint *top;
@property (nonatomic, strong, readonly) MASConstraint *right;
@property (nonatomic, strong, readonly) MASConstraint *bottom;
//首部
@property (nonatomic, strong, readonly) MASConstraint *leading;
//尾部
@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;
//文本基線
@property (nonatomic, strong, readonly) MASConstraint *baseline;
約束的特殊屬性
//(top, left, bottom, right)
@property (nonatomic, strong, readonly) MASConstraint *edges;
//(width, height)
@property (nonatomic, strong, readonly) MASConstraint *size;
//(centerX, centerY)
@property (nonatomic, strong, readonly) MASConstraint *center;
注意點(diǎn)：
1.使用Masonry不需要設(shè)置控件的translatesAutoresizingMaskIntoConstraints屬性為NO，mas_makeConstraints和mas_updateConstraints以及mas_remakeConstraints內(nèi)部已經(jīng)幫我們?cè)O(shè)置了;
- (NSArray *)mas_makeConstraints:(void(^)(MASConstraintMaker *))block {
self.translatesAutoresizingMaskIntoConstraints = NO;
MASConstraintMaker *constraintMaker = [[MASConstraintMaker alloc] initWithView:self];
block(constraintMaker);
return [constraintMaker install];
}
2.mas_makeConstraints和mas_updateConstraints以及mas_remakeConstraints的block是局部引用,block 里用到了 self，那 block 會(huì)保持一個(gè) self 的引用，但是 self 并沒(méi)有直接或者間接持有 block，所以不會(huì)造成循環(huán)引用。因此__weak typeof (self) weakSelf = self是沒(méi)必要的
3.添加約束一定要放addSubview之后，否則程序會(huì)崩潰
基本使用
UIView *blueView = [[UIView alloc]init];
blueView.backgroundColor = [UIColor blueColor];
[self.view addSubview:blueView];
[blueView mas_makeConstraints:^(MASConstraintMaker *make) {
//設(shè)置blueView的中心點(diǎn)的x等于self.view的中心點(diǎn)的x
make.centerX.equalTo(self.view);
//設(shè)置blueView的頂部等于self.view的頂部，同時(shí)偏移30
make.top.equalTo(self.view).offset(30);
//設(shè)置寬高都為90
make.size.mas_equalTo(CGSizeMake(90, 90));
}];
UIView *blackView = [[UIView alloc]init];
blackView.backgroundColor = [UIColor blackColor];
[self.view addSubview:blackView];
[blackView mas_makeConstraints:^(MASConstraintMaker *make) {
make.top.equalTo(blueView.mas_bottom).offset(20);
make.right.equalTo(blueView.mas_left).offset(20);
make.size.mas_equalTo(CGSizeMake(100, 100));
}];
UIView *greenView = [[UIView alloc]init];
greenView.backgroundColor = [UIColor greenColor];
[self.view addSubview:greenView];
[greenView mas_makeConstraints:^(MASConstraintMaker *make) {
make.size.mas_equalTo(CGSizeMake(200, 50));
make.center.equalTo(self.view);
}];
equalTo和mas_equalTo的區(qū)別
先觀察源碼：
#define mas_equalTo(...) equalTo(MASBoxValue((__VA_ARGS__)))
mas_equalTo會(huì)對(duì)參數(shù)進(jìn)行一個(gè)MASBoxValue（）操作，可以支持的類型是：NSNumber、 CGPoint、CGSize、UIEdgeInsets
/**
* Sets the constraint relation to NSLayoutRelationEqual
* returns a block which accepts one of the following:
* MASViewAttribute, UIView, NSValue, NSArray
* see readme for more details.
*/
- (MASConstraint * (^)(id attr))equalTo;
equalTo并沒(méi)有MASBoxValue（）操作，源碼的注釋上說(shuō)了equalTo支持的類型是：MASViewAttribute, UIView, NSValue, NSArray
為了方便編碼的2個(gè)宏
1.#define MAS_SHORTHAND：可以省略'mas_'前綴
2.#define MAS_SHORTHAND_GLOBALS：自動(dòng)將結(jié)構(gòu)體包裝成 NSValue，而無(wú)需再使用 mas_equalTo，其源碼如下：
#ifdef MAS_SHORTHAND_GLOBALS
#define equalTo(...) mas_equalTo(__VA_ARGS__)
