IOS VFL屏幕自适应

 -(void)fun1{
     //注意使用VFL，不用设置视图的frame
     UIView *view = [[UIView alloc] init];
     view.backgroundColor = [UIColor brownColor];
     [self.view addSubview:view];

     view.translatesAutoresizingMaskIntoConstraints = NO;//注意，要想使约束条件起作用，必须将此属性设置为no

     /*
      VFL相关的标识符
      H:代表水平方向
      V:代表垂直方向
      |代表父视图
      - 代表距离 例（H:|-20-）表示距离父视图左侧20像素
      []代表子视图相关属性
      */

     //对子视图View进行约束设置，format表示要设置的约束语句，在本句中意思为：view距离父视图左侧30像素，距离父视图右侧20像素（如果没设置具体的数字，且写了-）
     //options代表对其方式，默认写0就行
     //metrics 这里是一个字典，当在format中使用了动态数据比如上现这句:@"H:|-[button(==width)]-|",表示这个button的宽度为width,那么这个参数去哪里找呢？就是在这个字典里面找到key对应的值，如果没有找到这个值，app会crash
     //views 代表约束条件中所涉及的所有视图（父视图除外）
     NSArray *arr = [NSLayoutConstraint constraintsWithVisualFormat:@"H:|-30-[view]-|" options: metrics:nil views:NSDictionaryOfVariableBindings(view)];
 /*这里用到了一个系统宏定义,NSDictionaryOfVariableBindings(),其作用是生成一个词典,key的名字和对象的标识符相同,以上述为例,生成的词典形式就是{"self.view":self.view,@"_view3":_view3,...},这个词典应当包含需要自动布局的父视图和所有的子视图,
 */
     NSArray *arr1 = [NSLayoutConstraint constraintsWithVisualFormat:@"V:|-20-[view]-|" options: metrics:nil views:NSDictionaryOfVariableBindings(view)];

     [self.view addConstraints:arr];
     [self.view addConstraints:arr1];

 }

 -(void)fun2{
     UIView *view = [[UIView alloc] init];
     view.backgroundColor = [UIColor grayColor];
     [self.view addSubview:view];

     view.translatesAutoresizingMaskIntoConstraints =  NO;
     //[view(>=200)]  表示给view设置尺寸，此时小括号里的关系运算符只能是 == <= >=，注意，改尺寸的值不要与约束冲突，==：约束可以不写，简写成H:[view(==200)]    >=：当左右距离只设置了一个或者都未设置，视图的尺寸为最小值，如果两个都设置时，view 的尺寸为屏幕宽度减去左右距离，此时要保证减后的值>=尺寸最小值

     NSArray *arr = [NSLayoutConstraint constraintsWithVisualFormat:@"H:|-[view(>=200)]" options: metrics:nil views:NSDictionaryOfVariableBindings(view)];

      NSArray *arr1 = [NSLayoutConstraint constraintsWithVisualFormat:@"V:|-20-[view(==100)]" options: metrics:nil views:NSDictionaryOfVariableBindings(view)];
     [self.view addConstraints:arr1];
     [self.view addConstraints:arr];

 }

 -(void)fun3{
     UIView *view = [[UIView alloc] init];
     view.backgroundColor = [UIColor grayColor];
     [self.view addSubview:view];

     view.translatesAutoresizingMaskIntoConstraints =  NO;

     CGFloat width = ;

     //当我们在设置约束条件时，距离父视图上下左右的像素值以及view的尺寸不是固定的数字(用某个字符串代替)，这时我们需要给metrics设置一个字典，该字典的key必须是约束语句中使用的字符串，对应的value可以自行设置
     NSArray *arr = [NSLayoutConstraint constraintsWithVisualFormat:@"H:|-left-[view(==width)]" options: metrics:@{@"width":[NSNumber numberWithFloat:width],@"left":@} views:NSDictionaryOfVariableBindings(view)];

     NSArray *arr1 = [NSLayoutConstraint constraintsWithVisualFormat:@"V:|-20-[view(==100)]" options: metrics:nil views:NSDictionaryOfVariableBindings(view)];
     [self.view addConstraints:arr1];
     [self.view addConstraints:arr];

 }

 -(void)fun4{
     UIView *view = [[UIView alloc] init];
     view.backgroundColor = [UIColor grayColor];
     [self.view addSubview:view];

     view.translatesAutoresizingMaskIntoConstraints =  NO;

     CGFloat width = ;

     //当我们在设置约束条件时，距离父视图上下左右的像素值以及view的尺寸不是固定的数字(用某个字符串代替)，这时我们需要给metrics设置一个字典，该字典的key必须是约束语句中使用的字符串，对应的value可以自行设置
     NSArray *arr = [NSLayoutConstraint constraintsWithVisualFormat:@"H:|-left-[view(==width)]" options: metrics:@{@"width":[NSNumber numberWithFloat:width],@"left":@} views:NSDictionaryOfVariableBindings(view)];

     NSArray *arr1 = [NSLayoutConstraint constraintsWithVisualFormat:@"V:|-20-[view(==100)]" options: metrics:nil views:NSDictionaryOfVariableBindings(view)];
     [self.view addConstraints:arr1];
     [self.view addConstraints:arr];

     UIView *view1 = [[UIView alloc] init];
     view1.backgroundColor = [UIColor purpleColor];
     [self.view addSubview:view1];

     view1.translatesAutoresizingMaskIntoConstraints = NO;

     //[view1(view)] 代表view1和view某个方向尺寸相同
     NSArray *arr2 = [NSLayoutConstraint constraintsWithVisualFormat:@"H:|-[view1(view)]-|" options: metrics:nil views:NSDictionaryOfVariableBindings(view1,view)];

     //V:[view]-[view1]-20-|：子视图view1垂直方向距离平级子视图view 8像素（默认）
     NSArray *arr3 = [NSLayoutConstraint constraintsWithVisualFormat:@"V:[view]-[view1]-20-|" options: metrics:nil views:NSDictionaryOfVariableBindings(view,view1)];
     [self.view addConstraints:arr2];
     [self.view addConstraints:arr3];

 }

 //用VFL实现label自适应
 -(void)fun5{
     UILabel *label = [[UILabel alloc] init];
     label.backgroundColor = [UIColor grayColor];
     label.numberOfLines = ;
     label.lineBreakMode = NSLineBreakByCharWrapping;
     label.text = @"hiwehfdiuwehdiowqhdoiwehjdoiuwehdiouwhediuwheioudhewiuodhwehoihiuhiuhiuhiluhiuhiuhiuhihuhuuhhuh";
     [self.view addSubview:label];
     label.translatesAutoresizingMaskIntoConstraints = NO;

     NSArray *arr = [NSLayoutConstraint constraintsWithVisualFormat:@"H:|-[label]-|" options: metrics:nil views:NSDictionaryOfVariableBindings(label)];

     NSArray *arr1 = [NSLayoutConstraint constraintsWithVisualFormat:@"V:|-20-[label]" options: metrics:nil views:NSDictionaryOfVariableBindings(label)];

     [self.view addConstraints:arr];
     [self.view addConstraints:arr1];
 }