iOS autolayout使用

随着苹果机型越来越多，多机型适配成了一个问题，有的计算屏幕大小 ,有的用autoresize,个人感觉最好用的还是苹果提供的autolayout.当然，每个人的喜好不一样，这就要看自已的喜好了。autolayout实现多机型适配主是用用到约束，通过约束能够定位控件的位置，前提是父视图的大小确定。

下面从最简单的开始说起，在视图中添加Button,父视图占整个屏幕大小是可以确定的

竖屏                                                                               横屏

下面看看代码的实现：如下

- (void)viewDidLoad {
    [super viewDidLoad];
    // Do any additional setup after loading the view, typically from a nib.

    UIButton *TopLeftBtn=[UIButton buttonWithType:UIButtonTypeRoundedRect];
    [TopLeftBtn setTitle:@"TopLeftBtn" forState:UIControlStateNormal];
    [TopLeftBtn setTitleColor:[UIColor blackColor] forState:UIControlStateNormal];
    [TopLeftBtn setBackgroundColor:[UIColor greenColor]];
   //关闭autoresize
    [TopLeftBtn setTranslatesAutoresizingMaskIntoConstraints:NO];
    [self.view addSubview:TopLeftBtn];
    //前约束  也叫左约束   离父视图self.view的左边间距为10像素
    NSLayoutConstraint *topLeftBtnleadingConstraint=[NSLayoutConstraint constraintWithItem:TopLeftBtn attribute:NSLayoutAttributeLeading relatedBy:NSLayoutRelationEqual toItem:self.view attribute:NSLayoutAttributeLeading multiplier:1 constant:10];
    [self.view addConstraint:topLeftBtnleadingConstraint];
    //上约束   离父视图self.view的上边间距为10像素
    NSLayoutConstraint *topLeftBtntopConstraint=[NSLayoutConstraint constraintWithItem:TopLeftBtn attribute:NSLayoutAttributeTop relatedBy:NSLayoutRelationEqual toItem:self.view attribute:NSLayoutAttributeTop multiplier:1 constant:10];
    [self.view addConstraint:topLeftBtntopConstraint];

    //右约束  离父视图self.view的右边间距为10像素
    NSLayoutConstraint *topLeftBtnRightConstraint=[NSLayoutConstraint constraintWithItem:TopLeftBtn attribute:NSLayoutAttributeTrailing relatedBy:NSLayoutRelationEqual toItem:self.view attribute:NSLayoutAttributeTrailing multiplier:1 constant:-10];
    [self.view addConstraint:topLeftBtnRightConstraint];

    //下约束  离父视图self.view的下边间距为10像素
    NSLayoutConstraint *topRightBtnBottomConstraint=[NSLayoutConstraint constraintWithItem:TopLeftBtn attribute:NSLayoutAttributeBottom relatedBy:NSLayoutRelationEqual toItem:self.view attribute:NSLayoutAttributeBottom multiplier:1 constant:-10];
    [self.view addConstraint:topRightBtnBottomConstraint];
}

添加上面4个约束就可以确定Button的大小了，好了就这么简单，这是一个简单的，如果来点复杂的呢，那好就看下面的了

竖屏                                                                                横屏

上面两个按钮，下面一个按钮，上面两按钮宽度一样，所有Button高度一样，所有间距都是10像素，下面上代码：

- (void)viewDidLoad {
    [super viewDidLoad];
    // Do any additional setup after loading the view, typically from a nib.

    UIButton *TopLeftBtn=[UIButton buttonWithType:UIButtonTypeRoundedRect];
    [TopLeftBtn setTitle:@"TopLeftBtn" forState:UIControlStateNormal];
    [TopLeftBtn setTitleColor:[UIColor blackColor] forState:UIControlStateNormal];
    [TopLeftBtn setBackgroundColor:[UIColor greenColor]];
    [TopLeftBtn setTranslatesAutoresizingMaskIntoConstraints:NO];
    [self.view addSubview:TopLeftBtn];

    UIButton *TopRightBtn=[UIButton buttonWithType:UIButtonTypeRoundedRect];
    [TopRightBtn setTitle:@"TopRightBtn" forState:UIControlStateNormal];
    [TopRightBtn setTitleColor:[UIColor blackColor] forState:UIControlStateNormal];
    [TopRightBtn setBackgroundColor:[UIColor redColor]];
    [TopRightBtn setTranslatesAutoresizingMaskIntoConstraints:NO];
    [self.view addSubview:TopRightBtn];

    UIButton *BottomBtn=[UIButton buttonWithType:UIButtonTypeRoundedRect];
    [BottomBtn setTitle:@"BottomBtn" forState:UIControlStateNormal];
    [BottomBtn setTitleColor:[UIColor blackColor] forState:UIControlStateNormal];
    [BottomBtn setBackgroundColor:[UIColor blueColor]];
    [BottomBtn setTranslatesAutoresizingMaskIntoConstraints:NO];
    [self.view addSubview:BottomBtn];

    //TopLeftBtn相对于self.view的左约束  距父视图self.view的左间距是10像素
    NSLayoutConstraint *topLeftBtnleadingConstraint=[NSLayoutConstraint constraintWithItem:TopLeftBtn attribute:NSLayoutAttributeLeading relatedBy:NSLayoutRelationEqual toItem:self.view attribute:NSLayoutAttributeLeading multiplier:1 constant:10];
    [self.view addConstraint:topLeftBtnleadingConstraint];

    //TopLeftBtn相对于self.view的上约束   距父视图self.view的上间距是 10像素
    NSLayoutConstraint *topLeftBtntopConstraint=[NSLayoutConstraint constraintWithItem:TopLeftBtn attribute:NSLayoutAttributeTop relatedBy:NSLayoutRelationEqual toItem:self.view attribute:NSLayoutAttributeTop multiplier:1 constant:10];
    [self.view addConstraint:topLeftBtntopConstraint];

    //TopRightBtn相对于TopLeftBtn的约束 TopRightBtn与TopLeftBtn的上平齐
    NSLayoutConstraint *topRightBtnTopConstraint=[NSLayoutConstraint constraintWithItem:TopRightBtn attribute:NSLayoutAttributeTop relatedBy:NSLayoutRelationEqual toItem:TopLeftBtn attribute:NSLayoutAttributeTop multiplier:1 constant:0];
    [self.view addConstraint:topRightBtnTopConstraint];

    //TopRightBtn相对于TopLeftBtn的约束 TopRightBtn的左边与TopLeftBtn的右边相差10像素
    NSLayoutConstraint *topRightBtnLeadConstraint=[NSLayoutConstraint constraintWithItem:TopRightBtn attribute:NSLayoutAttributeLeading relatedBy:NSLayoutRelationEqual toItem:TopLeftBtn attribute:NSLayoutAttributeTrailing multiplier:1 constant:10];
    [self.view addConstraint:topRightBtnLeadConstraint];

    //TopRightBtn相对于self.view的约束 TopRightBtn的右边与父视图的右边间距是10像素
    NSLayoutConstraint *topRightBtnTrailConstraint=[NSLayoutConstraint constraintWithItem:TopRightBtn attribute:NSLayoutAttributeTrailing relatedBy:NSLayoutRelationEqual toItem:self.view attribute:NSLayoutAttributeTrailing multiplier:1 constant:-10.0];
    [self.view addConstraint:topRightBtnTrailConstraint];

    //TopRightBtn与TopLeftBtn宽度相等
    NSLayoutConstraint *topRightAndLeftBtnWidthEqualConstraint=[NSLayoutConstraint constraintWithItem:TopRightBtn attribute:NSLayoutAttributeWidth relatedBy:NSLayoutRelationEqual toItem:TopLeftBtn attribute:NSLayoutAttributeWidth multiplier:1 constant:0];
    [self.view addConstraint:topRightAndLeftBtnWidthEqualConstraint];

    //TopRightBtn与TopLeftBtn高度相等
    NSLayoutConstraint *topRightAndLeftBtnHeightEqualConstraint=[NSLayoutConstraint constraintWithItem:TopRightBtn attribute:NSLayoutAttributeHeight relatedBy:NSLayoutRelationEqual toItem:TopLeftBtn attribute:NSLayoutAttributeHeight multiplier:1 constant:0];
    [self.view addConstraint:topRightAndLeftBtnHeightEqualConstraint];

    //TopLeftBtn与BottomBtn左对齐
    NSLayoutConstraint *bottomBtnleadingConstraint=[NSLayoutConstraint constraintWithItem:TopLeftBtn attribute:NSLayoutAttributeLeading relatedBy:NSLayoutRelationEqual toItem:BottomBtn attribute:NSLayoutAttributeLeading multiplier:1 constant:0];
    [self.view addConstraint:bottomBtnleadingConstraint];

    //TopRightBtn与BottomBtn左对齐
    NSLayoutConstraint *bottomBtnTrailConstraint=[NSLayoutConstraint constraintWithItem:TopRightBtn attribute:NSLayoutAttributeTrailing relatedBy:NSLayoutRelationEqual toItem:BottomBtn attribute:NSLayoutAttributeTrailing multiplier:1 constant:0];
    [self.view addConstraint:bottomBtnTrailConstraint];

    //BottomBtn的上边距约束离TopLeftBtn的底部为10像素
    NSLayoutConstraint *bottomBtnTopConstraint=[NSLayoutConstraint constraintWithItem:BottomBtn attribute:NSLayoutAttributeTop relatedBy:NSLayoutRelationEqual toItem:TopLeftBtn attribute:NSLayoutAttributeBottom multiplier:1 constant:10];
    [self.view addConstraint:bottomBtnTopConstraint];

    //BottomBtn的上边距约束离self.view的底部是10像素
    NSLayoutConstraint *bottomBtnBottomConstraint=[NSLayoutConstraint constraintWithItem:BottomBtn attribute:NSLayoutAttributeBottom relatedBy:NSLayoutRelationEqual toItem:self.view attribute:NSLayoutAttributeBottom multiplier:1 constant:-10];
    [self.view addConstraint:bottomBtnBottomConstraint];

    //TopLeftBtn的高度与BottomBtn的高度相同
    NSLayoutConstraint *bottomBtnHeightConstraint=[NSLayoutConstraint constraintWithItem:TopLeftBtn attribute:NSLayoutAttributeHeight relatedBy:NSLayoutRelationEqual toItem:BottomBtn attribute:NSLayoutAttributeHeight multiplier:1 constant:0];
    //multiplier百度是乘数  constant 常数

    [self.view addConstraint:bottomBtnHeightConstraint];

    //更新约束
//    [self.view setNeedsUpdateConstraints];
//
//    [self.view updateConstraintsIfNeeded];
}

就这么多是不是很方便，那我们现在来看哈约束是怎么实现定位的，如果手机是5s的话，像素就是640*1136 缩小一倍就是320*568

竖屏时：设三个Button的高度是x未知数，三个Button高度一样，10+x+10+x+10=568 --->x=269，三个按钮高度都是269像素。BottomBtn的宽度是10+y+10=320--->y=300,BottomBtn的宽就是300像素。现在主是计算TopLeftBtn  TopRightBtn的宽了，TopLeftBtn与TopRightBtn的宽相等，那么10+z+10+z+10=320-->z=145,他们的宽就是145像素了，现在一切就好说了

TopLeftBtn的frame 就是（10,10,145,269）   TopRightBtn的frame为（10+145+10,10,145,269）

BottomBtn的frame就是(10,10+269+10,145,269)

横屏一样，只不过是宽度换过来了，其他的一样。

如果是4s或者6  6plus只不过是屏幕尺寸不一样而已都按上面的公式计算，得出的frame也不一样，所以说只要你的约束加得好，就会控制控件的位置，实现多屏配适配。是不是觉得很好学，有些人会觉得代码写得太多了，确实这样一个一个加约束确实挺麻烦的，如果又想代码写得少，又想效果好，请听下回分解