一、概要
通过对iOS8界面布局的学习和总结,发现autolayout才是主角,autolayout是iOS6引入的新特性,当时还粗浅的学习了下,可是没有真正应用到项目中。随着iOS设备尺寸逐渐碎片化,纯粹的hard
code方式UI布局将会走向死角,而autoresizing方式也有其局限性,所以无论如何autolayout都将成为UI布局的重要方式。
前两篇以发烧友心态对iOS8界面布局的主要元素size class和autolayout进行了探索,发现要完全掌握autolayout需要大量的时间去实践总结。所以深入思考autolayout是很有必要的。你可能有和我同样的疑问,如下:
1、以后一律使用autolayout吗?除了在storyboard中使用autolayout,代码方式autolayout如何使用?
2、好像忽略了一个重要问题,就是view动画在autolayout如何实现?
3、autolayout有没有局限性和解决不了的问题?兼容性怎么样?效率怎么样?
4、……
二、研究开始
1、直接说以后都应该使用storyboard+autolayout感觉是不负责的说法,读了好多网络的帖子,最后总结如下情况使用autolayout会有帮助:
a 当需要展示的内容很多并且尺寸不固定;
b 程序需支持屏幕旋转(主要是iPad程序,iPhone程序横屏的场景有点非主流);
c 程序通用于iPhone和iPad;
但storyboard中使用autolayout有利有弊,好处当然是可视化,实现简单功能很节省时间,但也有弊端,例如不小心移动一个控件就会让弄乱那些约束。抛开storyboard而使用autolayout,就需要代码定义约束了,而且代码量也不是很大。当app中一些view的出现时根据网络数据来决定的时候,代码方式可能更合适。
先看一个简单的Demo:
例子1:新建一个Single View Application template项目Demo4,在rootView上添加一个绿颜色的view,使新添加的view四个边距离superView四边20点宽
效果如图:
使用storyboard来实现这个效果很简单,选中绿色view,然后添加4个相对于superview的边界约束,约束的数值设置为20,然后Update Frame就可以了,因为不区分iOS设备,所以size class可以设置为默认的wAny hAny。Demo下载
接下来使用代码来实现UI布局,目前有3种方法可以使用:(1)最基本的约束实现方式;(2)特殊格式化语言的约束实现方式;(3)第三方UIView-AutoLayout
(1)最基本的约束实现方式
[objc] view
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- <span style="font-size:12px;">- (void)viewDidLoad {
- [super viewDidLoad];
- // Do any additional setup after loading the view, typically from a nib.
- self.view.translatesAutoresizingMaskIntoConstraints =NO;
- UIView *newView = [UIView new];
- newView.backgroundColor = [UIColor greenColor];
- [self.view addSubview:newView];
- newView.translatesAutoresizingMaskIntoConstraints =NO;
- NSLayoutConstraint *constraint = nil;
- constraint = [NSLayoutConstraint constraintWithItem:newView
- attribute:NSLayoutAttributeLeading
- relatedBy:NSLayoutRelationEqual
- toItem:self.view
- attribute:NSLayoutAttributeLeading
- multiplier:1.0f
- constant:20];
- [self.view addConstraint:constraint];
- constraint = [NSLayoutConstraint constraintWithItem:newView
- attribute:NSLayoutAttributeTrailing
- relatedBy:NSLayoutRelationEqual
- toItem:self.view
- attribute:NSLayoutAttributeTrailing
- multiplier:1.0f
- constant:-20];
- [self.view addConstraint:constraint];
- constraint = [NSLayoutConstraint constraintWithItem:newView
- attribute:NSLayoutAttributeTop
- relatedBy:NSLayoutRelationEqual
- toItem:self.view
- attribute:NSLayoutAttributeTop
- multiplier:1.0f
- constant:20];
- [self.view addConstraint:constraint];
- constraint = [NSLayoutConstraint constraintWithItem:newView
- attribute:NSLayoutAttributeBottom
- relatedBy:NSLayoutRelationEqual
- toItem:self.view
- attribute:NSLayoutAttributeBottom
- multiplier:1.0f
- constant:-20];
- [self.view addConstraint:constraint];
- }</span>
(2)特殊格式化语言的约束实现方式
[objc] view
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- <span style="font-size:12px;">- (void)viewDidLoad {
- [super viewDidLoad];
- self.view.translatesAutoresizingMaskIntoConstraints =NO;
- UIView *newView = [UIView new];
- newView.backgroundColor = [UIColor greenColor];
- [self.view addSubview:newView];
- newView.translatesAutoresizingMaskIntoConstraints =NO;
- NSMutableArray *constraintArray = [NSMutableArray array];
- [constraintArray addObjectsFromArray:[NSLayoutConstraint constraintsWithVisualFormat:@"H:|-20-[newView]-20-|"
- options:0
- metrics:nil
- views:NSDictionaryOfVariableBindings(newView, self.view)]];
- [constraintArray addObjectsFromArray:[NSLayoutConstraint constraintsWithVisualFormat:@"V:|-20-[newView]-20-|"
- options:0
- metrics:nil
- views:NSDictionaryOfVariableBindings(newView, self.view)]];
- [self.view addConstraints:constraintArray];
- }</span>
(3)第三方UIView-AutoLayout
[objc] view
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- <span style="font-size:12px;">- (void)viewDidLoad {
- [super viewDidLoad];
- self.view.translatesAutoresizingMaskIntoConstraints =NO;
- UIView *newView = [UIView new];
- newView.backgroundColor = [UIColor greenColor];
- [self.view addSubview:newView];
- newView.translatesAutoresizingMaskIntoConstraints =NO;
- [newView autoPinEdgeToSuperviewEdge:ALEdgeLeading withInset:20.0f];
- [newView autoPinEdgeToSuperviewEdge:ALEdgeTrailing withInset:20.0f];
- [newView autoPinEdgeToSuperviewEdge:ALEdgeTop withInset:20.0f];
- [newView autoPinEdgeToSuperviewEdge:ALEdgeBottom withInset:20.0f];
- }</span>
以上3种方式都实现了我们想要的效果,看来代码实现autolayout也不是那么复杂!
例子2:通过上边例子我们实现一个简单的UI布局,下面来一个稍微复杂点的,把上一篇中提到3个view布局的那个例子用代码布局实现一下,但难度有所增加,当size class切换的时候,页面布局发生相应的改变,效果如图:
首先初始化3个View:
[objc] view
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- <span style="font-size:12px;">- (UIView *) alView {
- UIView *newView = [UIView new];
- newView.translatesAutoresizingMaskIntoConstraints =NO;
- return newView;
- }
- UIView *greenView = [self alView];
- greenView.backgroundColor = [UIColor greenColor];
- [self.view addSubview:greenView];
- UIView *yellowView = [self alView];
- yellowView.backgroundColor = [UIColor yellowColor];
- [self.view addSubview:yellowView];
- UIView *blueView = [self alView];
- blueView.backgroundColor = [UIColor blueColor];
- [self.view addSubview:blueView];</span>
接下来适配竖屏的约束:
[objc] view
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- <span style="font-size:12px;">- (NSMutableArray *) portraitConstraints:(UIView *)greenView :(UIView *)yellowView :(UIView *)blueView
- {
- NSMutableArray *constraintArray = [NSMutableArray array];
- [constraintArray addObjectsFromArray:[NSLayoutConstraint
- constraintsWithVisualFormat:@"H:|-20-[greenView]-20-[yellowView(==greenView)]-20-|" options:0 metrics:nil
- views:NSDictionaryOfVariableBindings(greenView, yellowView)]];
- [constraintArray addObjectsFromArray:[NSLayoutConstraint
- constraintsWithVisualFormat:@"V:|-20-[greenView]-20-[blueView(==greenView)]-20-|" options:0 metrics:nil
- views:NSDictionaryOfVariableBindings(greenView, blueView)]];
- [constraintArray addObjectsFromArray:[NSLayoutConstraint
- constraintsWithVisualFormat:@"V:|-20-[yellowView]-20-[blueView(==yellowView)]-20-|" options:0 metrics:nil
- views:NSDictionaryOfVariableBindings(yellowView, blueView)]];
- [constraintArray addObjectsFromArray:[NSLayoutConstraint
- constraintsWithVisualFormat:@"H:|-20-[blueView]-20-|" options:0 metrics:nil
- views:NSDictionaryOfVariableBindings(blueView)]];
- return constraintArray;
- }</span>
然后横屏的约束:
[objc] view
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- <span style="font-size:12px;">- (NSMutableArray *) landscapeConstraints:(UIView *)greenView :(UIView *)yellowView :(UIView *)blueView
- {
- NSMutableArray *constraintArray = [NSMutableArray array];
- [constraintArray addObjectsFromArray:[NSLayoutConstraint
- constraintsWithVisualFormat:@"H:|-20-[greenView]-20-[yellowView(==greenView)]-20-|" options:0 metrics:nil
- views:NSDictionaryOfVariableBindings(greenView, yellowView)]];
- [constraintArray addObjectsFromArray:[NSLayoutConstraint
- constraintsWithVisualFormat:@"V:|-20-[blueView]-20-[greenView(==blueView)]-20-|" options:0 metrics:nil
- views:NSDictionaryOfVariableBindings(greenView, blueView)]];
- [constraintArray addObjectsFromArray:[NSLayoutConstraint
- constraintsWithVisualFormat:@"V:|-20-[blueView]-20-[yellowView(==blueView)]-20-|" options:0 metrics:nil
- views:NSDictionaryOfVariableBindings(yellowView, blueView)]];
- [constraintArray addObjectsFromArray:[NSLayoutConstraint
- constraintsWithVisualFormat:@"H:|-20-[blueView]-20-|" options:0 metrics:nil
- views:NSDictionaryOfVariableBindings(blueView)]];
- return constraintArray;
- }</span>
最后还要处理屏幕旋转:
[objc] view
plaincopy
- <span style="font-size:12px;">- (void)willTransitionToTraitCollection:(UITraitCollection *)newCollection
- withTransitionCoordinator:(id <UIViewControllerTransitionCoordinator>)coordinator
- {
- [super willTransitionToTraitCollection:newCollection withTransitionCoordinator:coordinator];
- [coordinator animateAlongsideTransition:^(id <UIViewControllerTransitionCoordinatorContext> context) {
- if (newCollection.verticalSizeClass == UIUserInterfaceSizeClassCompact) {
- NSLog(@"%s----%d", __FUNCTION__, __LINE__);
- [self.view removeConstraints:self.view.constraints];
- [self.view addConstraints:[self landscapeConstraints:self.greenView_ :self.yellowView_ :self.blueView_]];
- } else {
- NSLog(@"%s----%d", __FUNCTION__, __LINE__);
- [self.view removeConstraints:self.view.constraints];
- [self.view addConstraints:[self portraitConstraints:self.greenView_ :self.yellowView_ :self.blueView_]];
- }
- [self.view setNeedsLayout];
- } completion:nil];
- }</span>
这样就实现了我们预期的效果,总结下来,auotlayout就是给view添加足够的约束,让view系统可以根据约束来计算出一个view的frame。动手练习一下吧!
2、view动画在autolayout实现
当布局发生改变时,相当于对子view进行重新布局,而子view重新布局调用 layoutIfNeeded,所以动画可以这样实现:
[objc] view
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- <span style="font-size:12px;">- (void)animateConstraints
- {
- [UIView animateWithDuration:0.5 animations:^{
- [self.view layoutIfNeeded];
- }];
- }</span>
Github上已经有Demo了!
3、autolayout有没有局限性和解决不了的问题?兼容性怎么样?效率怎么样?
autolayout对view transforms支持的不好,这里有帖子详细描述了这个问题。
至于兼容性,只从iOS6就已经提出了autolayout的概念,现在iOS5系统不是很多了,甚至iOS6系统都已经升级为iOS7,未来一段时间大部分用户应该是使用iOS7和iOS8系统,所以兼容性问题不会太大,但size
class是iOS8才有的概念,所以还有有一定的适配工作量。
效率话题这里有提到,有时间再细研究。
结束语:时间和体力总是有限的,标题是autolayout详解,可想达到详解还需要更多的时间去实践和总结,还有一些细节没有体现出来:
例如:
[objc] view
plaincopy
- <span style="font-size:12px;">[NSLayoutConstraint constraintsWithVisualFormat:@"H:|-20-[newView]-20-|"options:0 metrics:nil views:NSDictionaryOfVariableBindings(newView, self.view)]</span>
1、这其中各个参数的含义,另外约束还有个优先级的概念
2、@"H:|-20-[newView]-20-|" 这种可视化布局字符串的含义等等,有空再补充了!
本篇内容所有Demo
本篇中的橙色字体都是资源哦,,可点击继续学习深层次的哈!