ios 手写布局的几种方式
- Frame
- AutoLayout
- VFL
- Masonry
ios 布局的几种方式
1.Frame
UIView *view = [[UIView alloc] initWithFrame:CGRectMake(10, 20, 30, 40)];
2.AutoLayout
UILabel * label = [[UILabel alloc]init];
//使用代码布局 需要将这个属性设置为NO
label.translatesAutoresizingMaskIntoConstraints = NO;
label.backgroundColor = [UIColor redColor];
//创建x居中的约束
NSLayoutConstraint * constraintx = [NSLayoutConstraint constraintWithItem:label attribute:NSLayoutAttributeCenterX relatedBy:NSLayoutRelationEqual toItem:self.view attribute:NSLayoutAttributeCenterX multiplier:1 constant:0];
//创建y居中的约束
NSLayoutConstraint * constrainty = [NSLayoutConstraint constraintWithItem:label attribute:NSLayoutAttributeCenterY relatedBy:NSLayoutRelationEqual toItem:self.view attribute:NSLayoutAttributeCenterY multiplier:1 constant:0];
//创建宽度约束
NSLayoutConstraint * constraintw = [NSLayoutConstraint constraintWithItem:label attribute:NSLayoutAttributeWidth relatedBy:NSLayoutRelationEqual toItem:nil attribute:NSLayoutAttributeNotAnAttribute multiplier:1 constant:100];
//创建高度约束
NSLayoutConstraint * constrainth = [NSLayoutConstraint constraintWithItem:label attribute:NSLayoutAttributeHeight relatedBy:NSLayoutRelationEqual toItem:nil attribute:NSLayoutAttributeNotAnAttribute multiplier:1 constant:100];
//添加约束之前，必须将视图加在父视图上
[self.view addSubview:label];
[self.view addConstraints:@[constraintx,constrainty,constrainth,constraintw]];
3.VFL
Visual Format Language，即“可视化格式语言”。直接手写约束很复杂，使用VFL相对简单很多，但比较难进行调试。
UILabel * label = [[UILabel alloc]init];
[label addConstraints: [NSLayoutConstraint
constraintsWithVisualFormat:@"V:[view1]-8-[view2]"
options:NSLayoutFormatAlignAllLeading
metrics:nil
views:NSDictionaryOfVariableBindings(view1, view2)]];
[self.view addSubview:label];
4.Masonry
masonry是iOS布局控件的轻量级框架。其原理是通过链式调用的方式对NSLayoutConstraint进行封装，简化了控件的约束方式。
- 实现:
UILabel * label = [[UILabel alloc]init];
label.backgroundColor = [UIColor grayColor];
[self.view addSubview:label];
UIView *superView = self.view;
[label mas_makeConstraints:^(MASConstraintMaker *make) {
make.left.equalTo(superView).offset(100);
make.right.equalTo(superView).offset(-100);
make.top.equalTo(superView).offset(200);
make.bottom.equalTo(superView).offset(-200);
}];
- 解析
- 子控件调用mas_makeConstraints方法，mas_makeConstraints方法有个block参数（返回值为void,参数为MASContraintMaker的实例对象make）；
- block作为方法的参数就是隐式调用（block并没有真正调用，需要在方法内部，block()调用一次，才会真正执行block）；
- block的有一个MASContraintMaker类的实例make作为参数，让make去添加约束；
- MASContraintMaker类中有个可变数组的属性，用于保存约束；
- 执行mas_makeConstraints传入进行的block；
- 遍历数组中的约束，完成约束的安装；
3.点语法
- 每个点语法实际调用的getter方法，getter方法的返回值为实例对象本身，然后继续调用getter方法，就成为链式了。
- 结合代码进行具体解释：make.left.top.equalTo(@10);
- 我们对其分开解释：点语法返回的时一个新的约束newConstraint。
如:
make.left.top.equalTo(@10);
分开写就为:
newConstraint1 = make.left;
newConstraint2 = newConstraint1.top;
newConstraint2.equalTo(@10);
- (MASConstraint * (^)(id))equalTo {
return ^id(id attribute) {
return self.equalToWithRelation(attribute, NSLayoutRelationEqual);
};
}
4.具体调动步骤:
MASConstraintMaker类：
MASConstraintMaker类就是一个工厂类，负责创建MASConstraint类型的对象（依赖于MASConstraint接口，而不依赖于具体实现）
粗略步骤：
- UIView的类调用mas_makeConstraints方法
- mas_makeConstraints有个block参数，会做隐式回调
- 获得约束数组，通过install安装约束。
mas_makeConstraints方法解析
用户是UIView调用扩展的UIView+MASAdditions分类的mas_makeConstraints方法来为当前视图添加约束的。
mas_makeConstraints方法的返回值是一个数组（NSArray）,数组中所存放的就是当前视图中所添加的所有约束。因为Masonry框架对NSLayoutConstraint封装成了MASViewConstraint，所有此处数组中存储的是MASViewConstraint对象。
接下来来看mas_makeConstraints的参数，mas_makeConstraints测参数是一个类型为void(^)(MASConstraintMaker *)的匿名block（也就是匿名闭包），该闭包的返回值为void, 并且需要一个MASConstraintMaker工厂类的一个对象。该闭包的作用就是可以让mas_makeConstraints方法通过该block给MASConstraintMaker工厂类对象中的MAConstraint属性进行初始化。
//新建并添加约束
- (NSArray *)mas_makeConstraints:(void(^)(MASConstraintMaker *))block {
//关闭自动添加约束，由我们手动添加约束
self.translatesAutoresizingMaskIntoConstraints = NO;
//实例化constraintMaker对象，来操作接下来的约束
MASConstraintMaker *constraintMaker = [[MASConstraintMaker alloc] initWithView:self];
//block作为参数，这里完成隐式调用，完成回调，通过block将constraintMaker对象回调给用户让用户对constraintMaker中的MAConstraint类型的属性进行初始化。换句话说block中所做的事情就是之前用户设置约束是所添加的代码，比如make.top(@10) == ( constraintMaker.top = 10 )。
block(constraintMaker);
//添加约束，但会Install的约束数组
return [constraintMaker install];
}
block参数的隐式回调
返回的值为一个block,block的返回值是MASConstraint类的实例对象，所以最终还是返回的MASConstraint类的实例对象。
- (MASConstraint * (^)(id))equalTo {
return ^id(id attribute) {
return self.equalToWithRelation(attribute, NSLayoutRelationEqual);
};
}
install
1.判断是否有约束，有就遍历约束，调用uninstall清空之前所有的约束
2.无约束，就遍历数组的约束对象，然后调用install逐个安装
3.调用系统的方法安装约束
- (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];
}
}
