Masonry介紹
Masonry是一個對系統NSLayoutConstraint進行封裝的第三方自動布局框架，采用鏈式編程的方式提供給開發者API。系統AutoLayout支持的操作，Masonry都支持，相比系統API功能來說，Masonry是有過之而無不及。
Masonry框架的基本結構
Masonry文件結構圖
首先我們看Masonry.h文件
#import <Foundation/Foundation.h>
//! Project version number for Masonry.
FOUNDATION_EXPORT double MasonryVersionNumber;
//! Project version string for Masonry.
FOUNDATION_EXPORT const unsigned char MasonryVersionString[];
#import "MASUtilities.h"
#import "View+MASAdditions.h"
#import "View+MASShorthandAdditions.h"
#import "ViewController+MASAdditions.h"
#import "NSArray+MASAdditions.h"
#import "NSArray+MASShorthandAdditions.h"
#import "MASConstraint.h"
#import "MASCompositeConstraint.h"
#import "MASViewAttribute.h"
#import "MASViewConstraint.h"
#import "MASConstraintMaker.h"
#import "MASLayoutConstraint.h"
#import "NSLayoutConstraint+MASDebugAdditions.h"
MASConstraint約束抽象類
MASCompositeConstraint試圖組合約束類
MASViewAttribute試圖屬性類，用于創建約束
MASViewConstraint試圖約束類，依賴于視圖屬性類
MASConstraintMaker創建約束的工廠方法
MASLayoutConstraint約束屬性，對NSLayoutConstraint的封裝
約束入口
我們都是對視圖進行約束，所以入口就是一個UIView的分類 View+MASAdditions.h
/**
* following properties return a new MASViewAttribute with current view and appropriate NSLayoutAttribute
*/
@property (nonatomic, strong, readonly) MASViewAttribute *mas_left;
@property (nonatomic, strong, readonly) MASViewAttribute *mas_top;
@property (nonatomic, strong, readonly) MASViewAttribute *mas_right;
@property (nonatomic, strong, readonly) MASViewAttribute *mas_bottom;
@property (nonatomic, strong, readonly) MASViewAttribute *mas_leading;
@property (nonatomic, strong, readonly) MASViewAttribute *mas_trailing;
@property (nonatomic, strong, readonly) MASViewAttribute *mas_width;
@property (nonatomic, strong, readonly) MASViewAttribute *mas_height;
@property (nonatomic, strong, readonly) MASViewAttribute *mas_centerX;
@property (nonatomic, strong, readonly) MASViewAttribute *mas_centerY;
@property (nonatomic, strong, readonly) MASViewAttribute *mas_baseline;
@property (nonatomic, strong, readonly) MASViewAttribute *(^mas_attribute)(NSLayoutAttribute attr);
@property (nonatomic, strong, readonly) MASViewAttribute *mas_firstBaseline;
@property (nonatomic, strong, readonly) MASViewAttribute *mas_lastBaseline;
#if TARGET_OS_IPHONE || TARGET_OS_TV
@property (nonatomic, strong, readonly) MASViewAttribute *mas_leftMargin;
@property (nonatomic, strong, readonly) MASViewAttribute *mas_rightMargin;
@property (nonatomic, strong, readonly) MASViewAttribute *mas_topMargin;
@property (nonatomic, strong, readonly) MASViewAttribute *mas_bottomMargin;
@property (nonatomic, strong, readonly) MASViewAttribute *mas_leadingMargin;
@property (nonatomic, strong, readonly) MASViewAttribute *mas_trailingMargin;
@property (nonatomic, strong, readonly) MASViewAttribute *mas_centerXWithinMargins;
@property (nonatomic, strong, readonly) MASViewAttribute *mas_centerYWithinMargins;
@property (nonatomic, strong, readonly) MASViewAttribute *mas_safeAreaLayoutGuide NS_AVAILABLE_IOS(11.0);
@property (nonatomic, strong, readonly) MASViewAttribute *mas_safeAreaLayoutGuideLeading NS_AVAILABLE_IOS(11.0);
@property (nonatomic, strong, readonly) MASViewAttribute *mas_safeAreaLayoutGuideTrailing NS_AVAILABLE_IOS(11.0);
@property (nonatomic, strong, readonly) MASViewAttribute *mas_safeAreaLayoutGuideLeft NS_AVAILABLE_IOS(11.0);
@property (nonatomic, strong, readonly) MASViewAttribute *mas_safeAreaLayoutGuideRight NS_AVAILABLE_IOS(11.0);
@property (nonatomic, strong, readonly) MASViewAttribute *mas_safeAreaLayoutGuideTop NS_AVAILABLE_IOS(11.0);
@property (nonatomic, strong, readonly) MASViewAttribute *mas_safeAreaLayoutGuideBottom NS_AVAILABLE_IOS(11.0);
@property (nonatomic, strong, readonly) MASViewAttribute *mas_safeAreaLayoutGuideWidth NS_AVAILABLE_IOS(11.0);
@property (nonatomic, strong, readonly) MASViewAttribute *mas_safeAreaLayoutGuideHeight NS_AVAILABLE_IOS(11.0);
@property (nonatomic, strong, readonly) MASViewAttribute *mas_safeAreaLayoutGuideCenterX NS_AVAILABLE_IOS(11.0);
@property (nonatomic, strong, readonly) MASViewAttribute *mas_safeAreaLayoutGuideCenterY NS_AVAILABLE_IOS(11.0);
#endif
這里，這些屬性返回一個當前view的一個新的MASViewAttribute以及合適的NSLayoutAttribute。
MASViewAttribute這個對象是一個存儲視圖和相關NSLayoutAttribute的不可變元組。描述約束方程左側或右側的一部分。
make構建約束
/**
* Creates a MASConstraintMaker with the callee view.
* Any constraints defined are added to the view or the appropriate superview once the block has finished executing
*
* @param block scope within which you can build up the constraints which you wish to apply to the view.
*
* @return Array of created MASConstraints
*/
- (NSArray *)mas_makeConstraints:(void(NS_NOESCAPE ^)(MASConstraintMaker *make))block;
該方法根據傳入的view創建一個MASConstraintMaker，一旦block結束執行，任何定義的約束都被添加到view或者合適的superview上。返回值就是一個創建的MASConstraints數組。
update約束
/**
* Creates a MASConstraintMaker with the callee view.
* Any constraints defined are added to the view or the appropriate superview once the block has finished executing.
* If an existing constraint exists then it will be updated instead.
*
* @param block scope within which you can build up the constraints which you wish to apply to the view.
*
* @return Array of created/updated MASConstraints
*/
- (NSArray *)mas_updateConstraints:(void(NS_NOESCAPE ^)(MASConstraintMaker *make))block;
該方法根據傳入的view創建一個MASConstraintMaker，一旦block結束執行，任何定義的約束都被添加到view或者合適的superview上。如果一個約束存在，那么它會替代到本次更新的約束。返回值是一個創建的/更新的約束的數組。
remake約束
/**
* Creates a MASConstraintMaker with the callee view.
* Any constraints defined are added to the view or the appropriate superview once the block has finished executing.
* All constraints previously installed for the view will be removed.
*
* @param block scope within which you can build up the constraints which you wish to apply to the view.
*
* @return Array of created/updated MASConstraints
*/
- (NSArray *)mas_remakeConstraints:(void(NS_NOESCAPE ^)(MASConstraintMaker *make))block;
該方法用于根據傳入的view創建一個MASConstraintMaker，一旦block結束執行，任何定義的約束都被添加到view或者合適的superview上。該view的所有以前的約束都將被remove掉，返回值是一個創建的/更新的約束的數組。該方法與update的區別是，update是更新相同的約束，而remake是完全刪除以前的約束，使用本次重新創建的約束。
MASConstraintMaker工廠類
這里MASConstraintMaker就是工廠方法，用于生成約束。具體負責創建MASConstraint類型的對象（依賴于MASConstraint接口，而不依賴于具體實現）。mas_makeConstraints方法中的Block的參數就是MASConstraintMaker的對象。用戶可以通過該Block回調過來的MASConstraintMaker對象給View指定要添加的約束以及該約束的值。該工廠中的.m文件中的constraints屬性數組就記錄了該工廠創建的所有MASConstraint對象。
1.MASAttribute枚舉
typedef NS_OPTIONS(NSInteger, MASAttribute) {
MASAttributeLeft = 1 << NSLayoutAttributeLeft,
MASAttributeRight = 1 << NSLayoutAttributeRight,
MASAttributeTop = 1 << NSLayoutAttributeTop,
MASAttributeBottom = 1 << NSLayoutAttributeBottom,
MASAttributeLeading = 1 << NSLayoutAttributeLeading,
MASAttributeTrailing = 1 << NSLayoutAttributeTrailing,
MASAttributeWidth = 1 << NSLayoutAttributeWidth,
MASAttributeHeight = 1 << NSLayoutAttributeHeight,
MASAttributeCenterX = 1 << NSLayoutAttributeCenterX,
MASAttributeCenterY = 1 << NSLayoutAttributeCenterY,
MASAttributeBaseline = 1 << NSLayoutAttributeBaseline,
MASAttributeFirstBaseline = 1 << NSLayoutAttributeFirstBaseline,
MASAttributeLastBaseline = 1 << NSLayoutAttributeLastBaseline,
#if TARGET_OS_IPHONE || TARGET_OS_TV
MASAttributeLeftMargin = 1 << NSLayoutAttributeLeftMargin,
MASAttributeRightMargin = 1 << NSLayoutAttributeRightMargin,
MASAttributeTopMargin = 1 << NSLayoutAttributeTopMargin,
MASAttributeBottomMargin = 1 << NSLayoutAttributeBottomMargin,
MASAttributeLeadingMargin = 1 << NSLayoutAttributeLeadingMargin,
MASAttributeTrailingMargin = 1 << NSLayoutAttributeTrailingMargin,
MASAttributeCenterXWithinMargins = 1 << NSLayoutAttributeCenterXWithinMargins,
MASAttributeCenterYWithinMargins = 1 << NSLayoutAttributeCenterYWithinMargins,
#endif
};
該枚舉其實就是對NSLayoutAttribute枚舉的一種封裝。
MASConstraint屬性
- 布局屬性定義
/**
* The following properties return a new MASViewConstraint
* with the first item set to the makers associated view and the appropriate MASViewAttribute
*/
@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;
#if TARGET_OS_IPHONE || TARGET_OS_TV
@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;
#endif
下面就以left屬性為例看一下實現。
- (MASConstraint *)left {
return [self addConstraintWithLayoutAttribute:NSLayoutAttributeLeft];
}
- (MASConstraint *)addConstraintWithLayoutAttribute:(NSLayoutAttribute)layoutAttribute {
return [self constraint:nil addConstraintWithLayoutAttribute:layoutAttribute];
}
這里，不管是left還是right或者center都會調用方法- (MASConstraint *)addConstraintWithLayoutAttribute:(NSLayoutAttribute)layoutAttribute，然后就是添加約束。這里依賴了兩個類，分別是MASViewAttribute和MASViewConstraint。
主要看一下下面這個方法，這個走的MASConstraint+Private.h文件中的代理MASConstraintDelegate，該代理中有兩個方法。
@protocol MASConstraintDelegate <NSObject>
/**
* Notifies the delegate when the constraint needs to be replaced with another constraint. For example
* A MASViewConstraint may turn into a MASCompositeConstraint when an array is passed to one of the equality blocks
*/
- (void)constraint:(MASConstraint *)constraint shouldBeReplacedWithConstraint:(MASConstraint *)replacementConstraint;
- (MASConstraint *)constraint:(MASConstraint *)constraint addConstraintWithLayoutAttribute:(NSLayoutAttribute)layoutAttribute;
@end
maker工廠方法中都實現了這個代理方法。
//代理方法實現
- (void)constraint:(MASConstraint *)constraint shouldBeReplacedWithConstraint:(MASConstraint *)replacementConstraint {
NSUInteger index = [self.constraints indexOfObject:constraint];
NSAssert(index != NSNotFound, @"Could not find constraint %@", constraint);
[self.constraints replaceObjectAtIndex:index withObject:replacementConstraint];
}
- (MASConstraint *)constraint:(MASConstraint *)constraint addConstraintWithLayoutAttribute:(NSLayoutAttribute)layoutAttribute {
//實例化MASViewAttribute
MASViewAttribute *viewAttribute = [[MASViewAttribute alloc] initWithView:self.view layoutAttribute:layoutAttribute];
//實例化MASViewConstraint
MASViewConstraint *newConstraint = [[MASViewConstraint alloc] initWithFirstViewAttribute:viewAttribute]; //判斷傳入的參數是不是MASViewConstraint類型，如果是進入if分支
if ([constraint isKindOfClass:MASViewConstraint.class]) {
//replace with composite constraint
NSArray *children = @[constraint, newConstraint];
//MASCompositeConstraint實例化并設置代理
MASCompositeConstraint *compositeConstraint = [[MASCompositeConstraint alloc] initWithChildren:children];
compositeConstraint.delegate = self;
//調用代理方法進行約束替換
[self constraint:constraint shouldBeReplacedWithConstraint:compositeConstraint];
return compositeConstraint;
}
//如果constraint為nil，那么就設置代理，并將新的約束添加到屬性數組constraints里面
if (!constraint) {
newConstraint.delegate = self;
[self.constraints addObject:newConstraint];
}
return newConstraint;
}
這里需要說明MASViewConstraint是MASConstraint的子類。通過NSLayoutAttribute創建一個MASConstraint并將創建的約束加入到數組constraints中，如果設置的是size、center等復合型的約束，則創建包含多個子約束的MASCompositeConstraint。
- block
/**
* Returns a block which creates a new MASCompositeConstraint with the first item set
* to the makers associated view and children corresponding to the set bits in the
* MASAttribute parameter. Combine multiple attributes via binary-or.
*/
@property (nonatomic, strong, readonly) MASConstraint *(^attributes)(MASAttribute attrs);
該只讀屬性返回一個block，該塊使用第一個item集創建新的MASCompositeConstraint與makers關聯的視圖和與MASAttribute參數中的設置位對應的子項。 通過binary-or組合多個屬性。
//該block是一個帶參數和帶返回值的block，傳入的是MASAttribute類型的參數返回的是MASConstraint，最后都是調用下面方法進行具體的實現。
- (MASConstraint *(^)(MASAttribute))attributes {
return ^(MASAttribute attrs){
return [self addConstraintWithAttributes:attrs];
};
}
- (MASConstraint *)addConstraintWithAttributes:(MASAttribute)attrs {
// 這里是列舉出所有可能的MASAttribute類型的布局
__unused MASAttribute anyAttribute = (MASAttributeLeft | MASAttributeRight | MASAttributeTop | MASAttributeBottom | MASAttributeLeading
| MASAttributeTrailing | MASAttributeWidth | MASAttributeHeight | MASAttributeCenterX
| MASAttributeCenterY | MASAttributeBaseline
| MASAttributeFirstBaseline | MASAttributeLastBaseline
#if TARGET_OS_IPHONE || TARGET_OS_TV
| MASAttributeLeftMargin | MASAttributeRightMargin | MASAttributeTopMargin | MASAttributeBottomMargin
| MASAttributeLeadingMargin | MASAttributeTrailingMargin | MASAttributeCenterXWithinMargins
| MASAttributeCenterYWithinMargins
#endif
);
//斷言，如果傳入的布局參數不再上面列舉出的布局類型中就拋出異常
NSAssert((attrs & anyAttribute) != 0, @"You didn't pass any attribute to make.attributes(...)");
//定義一個可變數據，并判斷attrs的類型，并將相應的布局添加到可變數組中
NSMutableArray *attributes = [NSMutableArray array];
if (attrs & MASAttributeLeft) [attributes addObject:self.view.mas_left];
if (attrs & MASAttributeRight) [attributes addObject:self.view.mas_right];
if (attrs & MASAttributeTop) [attributes addObject:self.view.mas_top];
if (attrs & MASAttributeBottom) [attributes addObject:self.view.mas_bottom];
if (attrs & MASAttributeLeading) [attributes addObject:self.view.mas_leading];
if (attrs & MASAttributeTrailing) [attributes addObject:self.view.mas_trailing];
if (attrs & MASAttributeWidth) [attributes addObject:self.view.mas_width];
if (attrs & MASAttributeHeight) [attributes addObject:self.view.mas_height];
if (attrs & MASAttributeCenterX) [attributes addObject:self.view.mas_centerX];
if (attrs & MASAttributeCenterY) [attributes addObject:self.view.mas_centerY];
if (attrs & MASAttributeBaseline) [attributes addObject:self.view.mas_baseline];
if (attrs & MASAttributeFirstBaseline) [attributes addObject:self.view.mas_firstBaseline];
if (attrs & MASAttributeLastBaseline) [attributes addObject:self.view.mas_lastBaseline];
#if TARGET_OS_IPHONE || TARGET_OS_TV
if (attrs & MASAttributeLeftMargin) [attributes addObject:self.view.mas_leftMargin];
if (attrs & MASAttributeRightMargin) [attributes addObject:self.view.mas_rightMargin];
if (attrs & MASAttributeTopMargin) [attributes addObject:self.view.mas_topMargin];
if (attrs & MASAttributeBottomMargin) [attributes addObject:self.view.mas_bottomMargin];
if (attrs & MASAttributeLeadingMargin) [attributes addObject:self.view.mas_leadingMargin];
if (attrs & MASAttributeTrailingMargin) [attributes addObject:self.view.mas_trailingMargin];
if (attrs & MASAttributeCenterXWithinMargins) [attributes addObject:self.view.mas_centerXWithinMargins];
if (attrs & MASAttributeCenterYWithinMargins) [attributes addObject:self.view.mas_centerYWithinMargins];
#endif
// 定義另外一個局部可變數組
NSMutableArray *children = [NSMutableArray arrayWithCapacity:attributes.count];
//遍歷上面的attributes可變數組，用其中的元素實例化MASViewConstraint對象并添加到新的children數組中
for (MASViewAttribute *a in attributes) {
[children addObject:[[MASViewConstraint alloc] initWithFirstViewAttribute:a]];
}
//根據數組children實例化MASCompositeConstraint對象，并作為返回值返回
MASCompositeConstraint *constraint = [[MASCompositeConstraint alloc] initWithChildren:children];
constraint.delegate = self;
[self.constraints addObject:constraint];
return constraint;
}
- edges、size和center
/**
* Creates a MASCompositeConstraint with type MASCompositeConstraintTypeEdges
* which generates the appropriate MASViewConstraint children (top, left, bottom, right)
* with the first item set to the makers associated view
*/
@property (nonatomic, strong, readonly) MASConstraint *edges;
/**
* Creates a MASCompositeConstraint with type MASCompositeConstraintTypeSize
* which generates the appropriate MASViewConstraint children (width, height)
* with the first item set to the makers associated view
*/
@property (nonatomic, strong, readonly) MASConstraint *size;
/**
* Creates a MASCompositeConstraint with type MASCompositeConstraintTypeCenter
* which generates the appropriate MASViewConstraint children (centerX, centerY)
* with the first item set to the makers associated view
*/
@property (nonatomic, strong, readonly) MASConstraint *center;
edges:根據MASCompositeConstraintTypeEdges類型創建一個MASCompositeConstraint對象，產生適合的MASViewConstraint子對象 (top, left, bottom, right)
size:根據MASCompositeConstraintTypeSize類型創建一個MASCompositeConstraint對象，產生適合的MASViewConstraint子對象 (width, height)
center:根據MASCompositeConstraintTypeCenter類型創建一個MASCompositeConstraint對象，產生適合的MASViewConstraint子對象 (centerX, centerY)
- updateExisting、removeExisting
/**
* Whether or not to check for an existing constraint instead of adding constraint
* 是否去檢查一個存在的約束，而不是添加約束
*/
@property (nonatomic, assign) BOOL updateExisting;
/**
* Whether or not to remove existing constraints prior to installing
* 在安裝約束前是否移除約束
*/
@property (nonatomic, assign) BOOL removeExisting;
下面我們看一下在maker工廠方法中的使用，如下所示：
- (NSArray *)install {
if (self.removeExisting) {
//取出當前view安裝的所有約束，并調用uninstall方法卸載約束。
NSArray *installedConstraints = [MASViewConstraint installedConstraintsForView:self.view];
for (MASConstraint *constraint in installedConstraints) {
[constraint uninstall];
}
}
NSArray *constraints = self.constraints.copy;
for (MASConstraint *constraint in constraints) {
constraint.updateExisting = self.updateExisting;
[constraint install];
}
[self.constraints removeAllObjects];
return constraints;
}
在maker工廠方法里面，遍歷屬性數組self.constraints，并調用MASConstraint的install方法安裝約束。在將設置好添加到constraints數組中的約束都設置好后就要開始把約束加到View上起作用，方法為install，邏輯如下：
如果是remake，也就是removeExisting =YES時，將已經添加上的約束全部uninstall，把本次maker里的所有創建的contraint設置好updateExisting，然后一個一個的install。
//MASConstraint.m文件中
- (void)install { MASMethodNotImplemented(); }
- (void)uninstall { MASMethodNotImplemented(); }
#define MASMethodNotImplemented() \
@throw [NSException exceptionWithName:NSInternalInconsistencyException \
reason:[NSString stringWithFormat:@"You must override %@ in a subclass.", NSStringFromSelector(_cmd)] \
userInfo:nil]
- group合并約束
該方法可以將多個maker中的多個約束合并為一個約束。
- (MASConstraint * (^)(dispatch_block_t))group;
//實現方法
- (MASConstraint *(^)(dispatch_block_t group))group {
return ^id(dispatch_block_t group) {
NSInteger previousCount = self.constraints.count;
group();
NSArray *children = [self.constraints subarrayWithRange:NSMakeRange(previousCount, self.constraints.count - previousCount)];
MASCompositeConstraint *constraint = [[MASCompositeConstraint alloc] initWithChildren:children];
constraint.delegate = self;
return constraint;
};
}
MASConstraint類解析
首先MASConstraint作為約束，是MASViewConstraint和MASCompositeConstraint的父類，其中MASViewConstraint指單個約束，而MASCompositeConstraint指復合約束。
#import "MASUtilities.h"
/**
* Enables Constraints to be created with chainable syntax
* Constraint can represent single NSLayoutConstraint (MASViewConstraint)
* or a group of NSLayoutConstraints (MASComposisteConstraint)
*/
@interface MASConstraint : NSObject
// Chaining Support
/**
* Modifies the NSLayoutConstraint constant,
* only affects MASConstraints in which the first item's NSLayoutAttribute is one of the following
* NSLayoutAttributeTop, NSLayoutAttributeLeft, NSLayoutAttributeBottom, NSLayoutAttributeRight
* 修改NSLayoutConstraint常數，僅僅影響第一個item的NSLayoutAttribute
* NSLayoutAttributeTop, NSLayoutAttributeLeft, NSLayoutAttributeBottom, NSLayoutAttributeRight之一的MASConstraints
*/
- (MASConstraint * (^)(MASEdgeInsets insets))insets;
/**
* Modifies the NSLayoutConstraint constant,
* only affects MASConstraints in which the first item's NSLayoutAttribute is one of the following
* NSLayoutAttributeTop, NSLayoutAttributeLeft, NSLayoutAttributeBottom, NSLayoutAttributeRight
* 修改NSLayoutConstraint常數，僅僅影響第一個item的NSLayoutAttribute
* NSLayoutAttributeTop, NSLayoutAttributeLeft, NSLayoutAttributeBottom, NSLayoutAttributeRight之一的MASConstraints
*/
- (MASConstraint * (^)(CGFloat inset))inset;
/**
* Modifies the NSLayoutConstraint constant,
* only affects MASConstraints in which the first item's NSLayoutAttribute is one of the following
* NSLayoutAttributeWidth, NSLayoutAttributeHeight
* 修改NSLayoutConstraint常數，僅僅影響第一個item的NSLayoutAttribute
* NSLayoutAttributeWidth, NSLayoutAttributeHeight 之一的MASConstraints
*/
- (MASConstraint * (^)(CGSize offset))sizeOffset;
/**
* Modifies the NSLayoutConstraint constant,
* only affects MASConstraints in which the first item's NSLayoutAttribute is one of the following
* NSLayoutAttributeCenterX, NSLayoutAttributeCenterY
* 修改NSLayoutConstraint常數，僅僅影響第一個item的NSLayoutAttribute
* NSLayoutAttributeCenterX, NSLayoutAttributeCenterY 之一的MASConstrain
*/
- (MASConstraint * (^)(CGPoint offset))centerOffset;
/**
* Modifies the NSLayoutConstraint constant
* 修改NSLayoutConstraint常數
*/
- (MASConstraint * (^)(CGFloat offset))offset;
/**
* Modifies the NSLayoutConstraint constant based on a value type
* 基于值類型，修改NSLayoutConstraint常數
*/
- (MASConstraint * (^)(NSValue *value))valueOffset;
/**
* Sets the NSLayoutConstraint multiplier property
*/
- (MASConstraint * (^)(CGFloat multiplier))multipliedBy;
/**
* Sets the NSLayoutConstraint multiplier to 1.0/dividedBy
*/
- (MASConstraint * (^)(CGFloat divider))dividedBy;
/**
* Sets the NSLayoutConstraint priority to a float or MASLayoutPriority
*/
- (MASConstraint * (^)(MASLayoutPriority priority))priority;
/**
* Sets the NSLayoutConstraint priority to MASLayoutPriorityLow
*/
- (MASConstraint * (^)(void))priorityLow;
/**
* Sets the NSLayoutConstraint priority to MASLayoutPriorityMedium
*/
- (MASConstraint * (^)(void))priorityMedium;
/**
* Sets the NSLayoutConstraint priority to MASLayoutPriorityHigh
*/
- (MASConstraint * (^)(void))priorityHigh;
/**
* 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;
/**
* Sets the constraint relation to NSLayoutRelationGreaterThanOrEqual
* returns a block which accepts one of the following:
* MASViewAttribute, UIView, NSValue, NSArray
* see readme for more details.
*/
- (MASConstraint * (^)(id attr))greaterThanOrEqualTo;
/**
* Sets the constraint relation to NSLayoutRelationLessThanOrEqual
* returns a block which accepts one of the following:
* MASViewAttribute, UIView, NSValue, NSArray
* see readme for more details.
*/
- (MASConstraint * (^)(id attr))lessThanOrEqualTo;
/**
* Optional semantic property which has no effect but improves the readability of constraint
*/
- (MASConstraint *)with;
/**
* Optional semantic property which has no effect but improves the readability of constraint
*/
- (MASConstraint *)and;
/**
* Creates a new MASCompositeConstraint with the called attribute and reciever
*/
- (MASConstraint *)left;
- (MASConstraint *)top;
- (MASConstraint *)right;
- (MASConstraint *)bottom;
- (MASConstraint *)leading;
- (MASConstraint *)trailing;
- (MASConstraint *)width;
- (MASConstraint *)height;
- (MASConstraint *)centerX;
- (MASConstraint *)centerY;
- (MASConstraint *)baseline;
- (MASConstraint *)firstBaseline;
- (MASConstraint *)lastBaseline;
#if TARGET_OS_IPHONE || TARGET_OS_TV
- (MASConstraint *)leftMargin;
- (MASConstraint *)rightMargin;
- (MASConstraint *)topMargin;
- (MASConstraint *)bottomMargin;
- (MASConstraint *)leadingMargin;
- (MASConstraint *)trailingMargin;
- (MASConstraint *)centerXWithinMargins;
- (MASConstraint *)centerYWithinMargins;
#endif
......省略
@end
1. 鏈式支持
#define MASEdgeInsets UIEdgeInsets
//MASConstraint.h
- (MASConstraint * (^)(MASEdgeInsets insets))insets;
//MASConstraint.m
- (MASConstraint * (^)(MASEdgeInsets))insets {
return ^id(MASEdgeInsets insets){
self.insets = insets;
return self;
};
}
//這是一個抽象方法，在MASConstraint類中沒有實現
- (void)setInsets:(MASEdgeInsets __unused)insets { MASMethodNotImplemented(); }
#define MASMethodNotImplemented() \
@throw [NSException exceptionWithName:NSInternalInconsistencyException \
reason:[NSString stringWithFormat:@"You must override %@ in a subclass.", NSStringFromSelector(_cmd)] \
userInfo:nil]
首先更新一下屬性self.insets，然后把自己self返回去。還記得工廠方法里面的maker嗎？它就會返回一個MASConstraint對象，這里我們調用上面的block然后就將自己返回去，你就可以一直用點語法install約束，這就是鏈式編程。
2.NSLayoutConstraint常數設置
MASConstraint的子類MASCompositeConstraint和MASViewConstraint中都進行了重寫并實現。
//MASCompositeConstraint.m
- (void)setInsets:(MASEdgeInsets)insets {
for (MASConstraint *constraint in self.childConstraints) {
constraint.insets = insets;
}
}
//MASViewConstraint.m
- (void)setInsets:(MASEdgeInsets)insets {
NSLayoutAttribute layoutAttribute = self.firstViewAttribute.layoutAttribute;
switch (layoutAttribute) {
case NSLayoutAttributeLeft:
case NSLayoutAttributeLeading:
self.layoutConstant = insets.left;
break;
case NSLayoutAttributeTop:
self.layoutConstant = insets.top;
break;
case NSLayoutAttributeBottom:
self.layoutConstant = -insets.bottom;
break;
case NSLayoutAttributeRight:
case NSLayoutAttributeTrailing:
self.layoutConstant = -insets.right;
break;
default:
break;
}
}
都是用來進行更改約束的。
3.NSLayoutConstraint Installation支持
/**
* Activates an NSLayoutConstraint if it's supported by an OS.
* Invokes install otherwise.
* 如果OS支持就激活一個NSLayoutConstraint，否則就調用install
*/
- (void)activate;
/**
* Deactivates previously installed/activated NSLayoutConstraint.
* 銷毀前面安裝或者激活的NSLayoutConstraint
*/
- (void)deactivate;
/**
* Creates a NSLayoutConstraint and adds it to the appropriate view.
* 創建一個NSLayoutConstraint并將它添加到合適的view上
*/
- (void)install;
/**
* Removes previously installed NSLayoutConstraint
* 移除以前安裝的NSLayoutConstraint
*/
- (void)uninstall;
//MASConstraint.m
- (void)activate { MASMethodNotImplemented(); }
- (void)deactivate { MASMethodNotImplemented(); }
- (void)install { MASMethodNotImplemented(); }
- (void)uninstall { MASMethodNotImplemented(); }
這四個方法都是抽象方法，均不在給類中實現，而是在子類MASCompositeConstraint和MASViewConstraint中都進行了重寫并實現。
下面看一下在子類中的實現情況。
//MASCompositeConstraint.m
- (void)activate {
for (MASConstraint *constraint in self.childConstraints) {
[constraint activate];
}
}
- (void)deactivate {
for (MASConstraint *constraint in self.childConstraints) {
[constraint deactivate];
}
}
- (void)install {
for (MASConstraint *constraint in self.childConstraints) {
constraint.updateExisting = self.updateExisting;
[constraint install];
}
}
- (void)uninstall {
for (MASConstraint *constraint in self.childConstraints) {
[constraint uninstall];
}
}
//MASViewConstraint.m
[self install];
}
- (void)deactivate {
[self uninstall];
}
- (void)install {
if (self.hasBeenInstalled) {
return;
}
if ([self supportsActiveProperty] && self.layoutConstraint) {
self.layoutConstraint.active = YES;
[self.firstViewAttribute.view.mas_installedConstraints addObject:self];
return;
}
MAS_VIEW *firstLayoutItem = self.firstViewAttribute.item;
NSLayoutAttribute firstLayoutAttribute = self.firstViewAttribute.layoutAttribute;
MAS_VIEW *secondLayoutItem = self.secondViewAttribute.item;
NSLayoutAttribute secondLayoutAttribute = self.secondViewAttribute.layoutAttribute;
// alignment attributes must have a secondViewAttribute
// therefore we assume that is refering to superview
// eg make.left.equalTo(@10)
if (!self.firstViewAttribute.isSizeAttribute && !self.secondViewAttribute) {
secondLayoutItem = self.firstViewAttribute.view.superview;
secondLayoutAttribute = firstLayoutAttribute;
}
MASLayoutConstraint *layoutConstraint
= [MASLayoutConstraint constraintWithItem:firstLayoutItem
attribute:firstLayoutAttribute
relatedBy:self.layoutRelation
toItem:secondLayoutItem
attribute:secondLayoutAttribute
multiplier:self.layoutMultiplier
constant:self.layoutConstant];
layoutConstraint.priority = self.layoutPriority;
layoutConstraint.mas_key = self.mas_key;
if (self.secondViewAttribute.view) {
MAS_VIEW *closestCommonSuperview = [self.firstViewAttribute.view mas_closestCommonSuperview:self.secondViewAttribute.view];
NSAssert(closestCommonSuperview,
@"couldn't find a common superview for %@ and %@",
self.firstViewAttribute.view, self.secondViewAttribute.view);
self.installedView = closestCommonSuperview;
} else if (self.firstViewAttribute.isSizeAttribute) {
self.installedView = self.firstViewAttribute.view;
} else {
self.installedView = self.firstViewAttribute.view.superview;
}
MASLayoutConstraint *existingConstraint = nil;
if (self.updateExisting) {
existingConstraint = [self layoutConstraintSimilarTo:layoutConstraint];
}
if (existingConstraint) {
// just update the constant
existingConstraint.constant = layoutConstraint.constant;
self.layoutConstraint = existingConstraint;
} else {
[self.installedView addConstraint:layoutConstraint];
self.layoutConstraint = layoutConstraint;
[firstLayoutItem.mas_installedConstraints addObject:self];
}
}
- (MASLayoutConstraint *)layoutConstraintSimilarTo:(MASLayoutConstraint *)layoutConstraint {
// check if any constraints are the same apart from the only mutable property constant
// go through constraints in reverse as we do not want to match auto-resizing or interface builder constraints
// and they are likely to be added first.
for (NSLayoutConstraint *existingConstraint in self.installedView.constraints.reverseObjectEnumerator) {
if (![existingConstraint isKindOfClass:MASLayoutConstraint.class]) continue;
if (existingConstraint.firstItem != layoutConstraint.firstItem) continue;
if (existingConstraint.secondItem != layoutConstraint.secondItem) continue;
if (existingConstraint.firstAttribute != layoutConstraint.firstAttribute) continue;
if (existingConstraint.secondAttribute != layoutConstraint.secondAttribute) continue;
if (existingConstraint.relation != layoutConstraint.relation) continue;
if (existingConstraint.multiplier != layoutConstraint.multiplier) continue;
if (existingConstraint.priority != layoutConstraint.priority) continue;
return (id)existingConstraint;
}
return nil;
}
- (void)uninstall {
if ([self supportsActiveProperty]) {
self.layoutConstraint.active = NO;
[self.firstViewAttribute.view.mas_installedConstraints removeObject:self];
return;
}
[self.installedView removeConstraint:self.layoutConstraint];
self.layoutConstraint = nil;
self.installedView = nil;
[self.firstViewAttribute.view.mas_installedConstraints removeObject:self];
}
4.MASConstraint分類
@interface MASConstraint (AutoboxingSupport)
/**
* Aliases to corresponding relation methods (for shorthand macros)
* Also needed to aid autocompletion
*/
- (MASConstraint * (^)(id attr))mas_equalTo;
- (MASConstraint * (^)(id attr))mas_greaterThanOrEqualTo;
- (MASConstraint * (^)(id attr))mas_lessThanOrEqualTo;
/**
* A dummy method to aid autocompletion
*/
- (MASConstraint * (^)(id offset))mas_offset;
@end
以- (MASConstraint * (^)(id attr))mas_equalTo;為例進行說明
- (MASConstraint * (^)(id))mas_equalTo {
return ^id(id attribute) {
return self.equalToWithRelation(attribute, NSLayoutRelationEqual);
};
}
- (MASConstraint * (^)(id, NSLayoutRelation))equalToWithRelation { MASMethodNotImplemented(); }
可見，這個在本抽象類還是沒有實現，在子類MASCompositeConstraint和MASViewConstraint中都進行了重寫并實現。
//MASCompositeConstraint.m
- (MASConstraint * (^)(id, NSLayoutRelation))equalToWithRelation {
return ^id(id attr, NSLayoutRelation relation) {
for (MASConstraint *constraint in self.childConstraints.copy) {
constraint.equalToWithRelation(attr, relation);
}
return self;
};
}
//MASViewConstraint.m
- (MASConstraint * (^)(id, NSLayoutRelation))equalToWithRelation {
return ^id(id attribute, NSLayoutRelation relation) {
if ([attribute isKindOfClass:NSArray.class]) {
NSAssert(!self.hasLayoutRelation, @"Redefinition of constraint relation");
NSMutableArray *children = NSMutableArray.new;
for (id attr in attribute) {
MASViewConstraint *viewConstraint = [self copy];
viewConstraint.layoutRelation = relation;
viewConstraint.secondViewAttribute = attr;
[children addObject:viewConstraint];
}
MASCompositeConstraint *compositeConstraint = [[MASCompositeConstraint alloc] initWithChildren:children];
compositeConstraint.delegate = self.delegate;
[self.delegate constraint:self shouldBeReplacedWithConstraint:compositeConstraint];
return compositeConstraint;
} else {
NSAssert(!self.hasLayoutRelation || self.layoutRelation == relation && [attribute isKindOfClass:NSValue.class], @"Redefinition of constraint relation");
self.layoutRelation = relation;
self.secondViewAttribute = attribute;
return self;
}
};
}
MASCompositeConstraint類解析
#import "MASConstraint.h"
#import "MASUtilities.h"
/**
* A group of MASConstraint objects
*/
@interface MASCompositeConstraint : MASConstraint
/**
* Creates a composite with a predefined array of children
*
* @param children child MASConstraints
*
* @return a composite constraint
*/
- (id)initWithChildren:(NSArray *)children;
@end
該類只有一個實例化方法，用于實例化對象，傳入的參數children，為約束數組，利用這個數組進行合成約束。
在其.m中不僅實現了這個實例化方法，還重寫了很多MASConstrain方法。并設置代理和實現了MASConstraintDelegate。我們首先看一下這個實例化方法。
@property (nonatomic, strong) NSMutableArray *childConstraints;
- (id)initWithChildren:(NSArray *)children {
self = [super init];
if (!self) return nil;
_childConstraints = [children mutableCopy];
for (MASConstraint *constraint in _childConstraints) {
constraint.delegate = self;
}
return self;
}
下面看一下內部的組織結構，如下圖所示：
MASCompositeConstraint
從這我們就可以看到Masonry的組織結構非常清爽，很多方法都在父類定義并在子類重寫，子類只保留了一個自定義的示例化方法。
MASViewConstraint類解析
該類是一個單約束，包含創建NSLayoutConstraint所需要的屬性，并將其添加到適合的view上.
/**
* A single constraint.
* Contains the attributes neccessary for creating a NSLayoutConstraint and adding it to the appropriate view
* NSLayoutConstraint的第一個item/view和第一個屬性
*/
@interface MASViewConstraint : MASConstraint <NSCopying>
/**
* First item/view and first attribute of the NSLayoutConstraint
* NSLayoutConstraint的第二個item/view和第二個屬性
*/
@property (nonatomic, strong, readonly) MASViewAttribute *firstViewAttribute;
/**
* Second item/view and second attribute of the NSLayoutConstraint
*/
@property (nonatomic, strong, readonly) MASViewAttribute *secondViewAttribute;
/**
* initialises the MASViewConstraint with the first part of the equation
*
* @param firstViewAttribute view.mas_left, view.mas_width etc.
*
* @return a new view constraint
*/
- (id)initWithFirstViewAttribute:(MASViewAttribute *)firstViewAttribute;
/**
* Returns all MASViewConstraints installed with this view as a first item.
*
* @param view A view to retrieve constraints for.
*
* @return An array of MASViewConstraints.
*/
+ (NSArray *)installedConstraintsForView:(MAS_VIEW *)view;
@end
- 實例化方法
@property (nonatomic, assign) MASLayoutPriority layoutPriority;
@property (nonatomic, assign) CGFloat layoutMultiplier;
- (id)initWithFirstViewAttribute:(MASViewAttribute *)firstViewAttribute {
self = [super init];
if (!self) return nil;
_firstViewAttribute = firstViewAttribute;
self.layoutPriority = MASLayoutPriorityRequired;
self.layoutMultiplier = 1;
return self;
}
- 返回所有安裝的約束
+ (NSArray *)installedConstraintsForView:(MAS_VIEW *)view {
return [view.mas_installedConstraints allObjects];
}
這里要用到一個MAS_VIEW（其實就是UIView）的一個分類。
@interface MAS_VIEW (MASConstraints)
@property (nonatomic, readonly) NSMutableSet *mas_installedConstraints;
@end
@implementation MAS_VIEW (MASConstraints)
static char kInstalledConstraintsKey;
- (NSMutableSet *)mas_installedConstraints {
NSMutableSet *constraints = objc_getAssociatedObject(self, &kInstalledConstraintsKey);
if (!constraints) {
constraints = [NSMutableSet set];
objc_setAssociatedObject(self, &kInstalledConstraintsKey, constraints, OBJC_ASSOCIATION_RETAIN_NONATOMIC);
}
return constraints;
}
@end
同MASCompositeConstraint類一樣，在.m文件里面MASViewConstraint也重寫了很多的父類的方法,結構很清晰。
下面看一下該類的結構
MASViewConstraint
在.h中只暴露出來一個實例化方法和返回所有已安裝約束的方法。在.m中重寫了很多父類的方法
