如何在scrollView中使用Autolayout

prat1 storyboard情况下进行约束布局  

scrollView比较特殊，因为它有个contentSize的属性。那么在遇到scrollView时，怎么使用Autolayout呢。其实关键点就一点：

ScrollView的contentSize的大小是由其subview的constraints来决定的。

 转：http://blog.cnbluebox.com/blog/2015/02/02/autolayout2/

向竖滚动步骤：

1.设置subview四个方向的边与scrollview四个方向的边相贴的约束。

2.设置subview和scrollview等宽和等高的约束，等高约束优先级要比subview后面具体高度的约束低。

3.设置subview具体高度的约束， 当改变该约束时与设置contentSize.heigth作用等效。

part2手写代码情况下进行约束布局

条件通过自定义scrollview，覆盖addSubview:和setContentSize:方法。添加一个subview，改变改subview的height值为目标的contentSize.height。

自定义scrollView的代码如下：

#import <UIKit/UIKit.h>

@interface MScrollView : UIScrollView

@property(nonatomic,strong,readonly)UIView * mContentView;

@end

.

#import "MScrollView.h"

@interface MScrollView ()
@property(nonatomic,strong) UIView * mContentView;
@end

@implementation MScrollView


-(instancetype)initWithFrame:(CGRect)frame{
    if (self=[super initWithFrame:frame]) {
        _mContentView = [[UIView alloc]initWithFrame:frame];
        [self addSubview:_mContentView];
    }
    return self;
}

-(void)addSubview:(UIView *)view{
    [super addSubview:view];
    if (view!=_mContentView) {
        [_mContentView addSubview:view];
    }else{
        [super addSubview:_mContentView];
    }
}

-(void)setContentSize:(CGSize)contentSize{
    _mContentView.frame = CGRectMake(self.frame.origin.x
                                     , self.frame.origin.y, contentSize.width, contentSize.height);
    [super setContentSize:contentSize];
}

@end

 .

- (void)viewDidLoad {
    [super viewDidLoad];
    
    self.scrollView = [[MScrollView alloc]initWithFrame:self.view.frame];
    self.scrollView.backgroundColor = [UIColor redColor];
    self.scrollView.contentSize = CGSizeMake([UIScreen mainScreen].bounds.size.width, 1000);
    [self.view addSubview:self.scrollView];
    
    UIView * blueView  =[[UIView alloc]init];
    blueView.backgroundColor =[ UIColor blueColor];
    blueView.tag = 1008;
    [self.scrollView.mContentView addSubview:blueView];
    
}

-(void)updateViewConstraints{
    [super updateViewConstraints];
    UIView *blueView = [self.scrollView.mContentView viewWithTag:1008];
    //
    CGFloat width = [UIScreen mainScreen].bounds.size.width;
    NSDictionary *metrics = @{@"width":@(width),@"height":@(200)};
    blueView.translatesAutoresizingMaskIntoConstraints = NO;
    [blueView.superview addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:@"H:[blueView(==width)]" options:0 metrics:metrics views:@{@"blueView":blueView}]];
    [blueView.superview addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:@"V:[blueView(==height)]" options:0 metrics:metrics views:@{@"blueView":blueView}]];
    [blueView.superview addConstraint:[NSLayoutConstraint constraintWithItem:blueView attribute:NSLayoutAttributeBottom relatedBy:NSLayoutRelationEqual toItem:blueView.superview attribute:NSLayoutAttributeBottom multiplier:1.0 constant:0]];

}