Masonry复杂ScrollView布局

前言

说到iOS自动布局，有很多的解决办法。有的人使用xib/storyboard自动布局，也有人使用frame来适配。对于前者，笔者并不喜欢，也不支持。对于后者，更是麻烦，到处计算高度、宽度等，千万大量代码的冗余，对维护和开发的效率都很低。

笔者在这里介绍纯代码自动布局的第三方库：Masonry。这个库使用率相当高，在全世界都有大量的开发者在使用，其star数量也是相当高的。

效果图

本节详解Masonry的循环创建视图，并且可以展开与收缩的用法，先看看效果图：

当我们点击某一行时，可以展开：

核心代码

看下代码：

 

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@interface ScrollViewComplexController ()   @property (nonatomic, strong) UIScrollView *scrollView; @property (nonatomic, strong) NSMutableArray *expandStates;   @end   @implementation ScrollViewComplexController   - (void)viewDidLoad {   [super viewDidLoad];     self.scrollView = [[UIScrollView alloc] init];   self.scrollView.pagingEnabled = NO;   [self.view addSubview:self.scrollView];   self.scrollView.backgroundColor = [UIColor lightGrayColor];      CGFloat screenWidth = [UIScreen mainScreen].bounds.size.width;   UILabel *lastLabel = nil;   for (NSUInteger i = 0; i < 10; ++i) {     UILabel *label = [[UILabel alloc] init];     label.numberOfLines = 0;     label.layer.borderColor = [UIColor greenColor].CGColor;     label.layer.borderWidth = 2.0;     label.text = [self randomText];     label.userInteractionEnabled = YES;     UITapGestureRecognizer *tap = [[UITapGestureRecognizer alloc] initWithTarget:self action:@selector(onTap:)];     [label addGestureRecognizer:tap];          // We must preferredMaxLayoutWidth property for adapting to iOS6.0     label.preferredMaxLayoutWidth = screenWidth - 30;     label.textAlignment = NSTextAlignmentLeft;     label.textColor = [self randomColor];     [self.scrollView addSubview:label];          [label mas_makeConstraints:^(MASConstraintMaker *make) {       make.left.mas_equalTo(15);       make.right.mas_equalTo(self.view).offset(-15);              if (lastLabel) {         make.top.mas_equalTo(lastLabel.mas_bottom).offset(20);       } else {         make.top.mas_equalTo(self.scrollView).offset(20);       }              make.height.mas_equalTo(40);     }];          lastLabel = label;          [self.expandStates addObject:[@[label, @(NO)] mutableCopy]];   }      [self.scrollView mas_makeConstraints:^(MASConstraintMaker *make) {     make.edges.mas_equalTo(self.view);          // 让scrollview的contentSize随着内容的增多而变化     make.bottom.mas_equalTo(lastLabel.mas_bottom).offset(20);   }]; }   - (NSMutableArray *)expandStates {   if (_expandStates == nil) {     _expandStates = [[NSMutableArray alloc] init];   }      return _expandStates; }   - (UIColor *)randomColor {   CGFloat hue = ( arc4random() % 256 / 256.0 );  //  0.0 to 1.0   CGFloat saturation = ( arc4random() % 128 / 256.0 ) + 0.5;  //  0.5 to 1.0, away from white   CGFloat brightness = ( arc4random() % 128 / 256.0 ) + 0.5;  //  0.5 to 1.0, away from black   return [UIColor colorWithHue:hue saturation:saturation brightness:brightness alpha:1]; }   - (NSString *)randomText {   CGFloat length = arc4random() % 150 + 5;      NSMutableString *str = [[NSMutableString alloc] init];   for (NSUInteger i = 0; i < length; ++i) {     [str appendString:@"测试数据很长，"];   }      return str; }   - (void)onTap:(UITapGestureRecognizer *)sender {   UIView *tapView = sender.view;      NSUInteger index = 0;   for (NSMutableArray *array in self.expandStates) {     UILabel *view = [array firstObject];          if (view == tapView) {       NSNumber *state = [array lastObject];              if ([state boolValue] == YES) {         [view mas_updateConstraints:^(MASConstraintMaker *make) {           make.height.mas_equalTo(40);         }];       } else {         UIView *preView = nil;         UIView *nextView = nil;                  if (index - 1 < self.expandStates.count && index >= 1) {           preView = [[self.expandStates objectAtIndex:index - 1] firstObject];         }                  if (index + 1 < self.expandStates.count) {            nextView = [[self.expandStates objectAtIndex:index + 1] firstObject];         }           [view mas_remakeConstraints:^(MASConstraintMaker *make) {           if (preView) {             make.top.mas_equalTo(preView.mas_bottom).offset(20);           } else {             make.top.mas_equalTo(20);           }                      make.left.mas_equalTo(15);           make.right.mas_equalTo(self.view).offset(-15);         }];                  if (nextView) {           [nextView mas_updateConstraints:^(MASConstraintMaker *make) {             make.top.mas_equalTo(view.mas_bottom).offset(20);           }];         }       }              [array replaceObjectAtIndex:1 withObject:@(!state.boolValue)];              [self.view setNeedsUpdateConstraints];       [self.view updateConstraintsIfNeeded];         [UIView animateWithDuration:0.35 animations:^{         [self.view layoutIfNeeded];       } completion:^(BOOL finished) {         }];       break;     }          index++;   } }   @end

讲解

当我们要收起的时候，只是简单地设置其高度的约束为40，但是当我们要展开时，实现起来就相对麻烦了。因为我们需要重新添加约束，要重新给所点击的视图添加约束，就需要知道前一个依赖视图和后一个依赖视图的约束，以便将相关联的都更新约束。

当我们更新所点击的视图时，我们通过判断是否有前一个依赖视图来设置顶部约束：

 

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if (preView) {     make.top.mas_equalTo(preView.mas_bottom).offset(20); } else {     make.top.mas_equalTo(20); }

除了这个之外，我们也需要更新后一个视图的约束，因为我们对所点击的视图调用了mas_remakeConstraints方法，就会移除其之前所添加的所有约束，所以我们必须重新将后者对当前点击的视图的依赖重新添加上去：

 

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if (nextView) {   [nextView mas_updateConstraints:^(MASConstraintMaker *make) {     make.top.mas_equalTo(view.mas_bottom).offset(20);   }]; }