IOS之Autolayout简单实用

IOS中AutoLayout是自动布局，利用Autolayout来做屏幕适配，很方便，直接上代码：

- (void)viewDidLoad {

    [super viewDidLoad];

    //创建一个新的UIView

    UIView *newview = [[UIView alloc]init];

    newview.backgroundColor = [UIColor grayColor];

    //要使用Autolayout必须先把view添加到父view中去，否则编译时候会警告

    [self.view addSubview:newview];

    ////要使用Autolayout必须先把该view的translatesAutoresizingMaskIntoConstraints属性这只为NO

    newview.translatesAutoresizingMaskIntoConstraints = NO;

    NSLayoutConstraint *contraint = nil;

    //距离首部20,等价于左侧

    contraint = [NSLayoutConstraint constraintWithItem:newview attribute:NSLayoutAttributeLeading relatedBy:NSLayoutRelationEqual toItem:self.view attribute:NSLayoutAttributeLeading multiplier:1.0 constant:20];

    //添加左侧约束

    [self.view addConstraint:contraint];

    //距离尾部-20，等价与右侧

    contraint = [NSLayoutConstraint constraintWithItem:newview attribute:NSLayoutAttributeTrailing relatedBy:NSLayoutRelationEqual toItem:self.view attribute:NSLayoutAttributeTrailing multiplier:1.0f constant:-20];

    //添加右侧约束

    [self.view addConstraint:contraint];

    

    //距离上侧50

    contraint = [NSLayoutConstraint constraintWithItem:newview attribute:NSLayoutAttributeTop relatedBy:NSLayoutRelationEqual toItem:self.view attribute:NSLayoutAttributeTop multiplier:1.0f constant:50];

    //添加上侧约束

    [self.view addConstraint:contraint];

    

    //距离下侧-20

    contraint  = [NSLayoutConstraint constraintWithItem:newview attribute:NSLayoutAttributeBottom relatedBy:NSLayoutRelationEqual toItem:self.view attribute:NSLayoutAttributeBottom multiplier:1.0f constant:-20];

    //添加下侧约束

    [self.view addConstraint:contraint];

}

在任何模拟器上运行，newview距离上下左右边的距离均为50，-20，20，-20.