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); }]; } |