• (void)viewDidLoad {
  [super viewDidLoad];

  UIView *view = [[UIView alloc] init];
  view.backgroundColor = [UIColor redColor];

  //用Constraints（layout）來布局;哪個(gè)視圖（view）使用layout布局哪個(gè)控件就必須寫這句話
  [view setTranslatesAutoresizingMaskIntoConstraints:NO];
  [self.view addSubview:view];

  //****************** 給視圖添加約束的四個(gè)步驟 ***************************
  //被添加的約束對(duì)象的superView
  //第一個(gè)參數(shù):表示被添加約束的對(duì)象；
  //第二個(gè)參數(shù):表示被約束的方向；是一個(gè)枚舉值；
  /*
  NSLayoutAttributeLeft = 1,
  NSLayoutAttributeRight,
  NSLayoutAttributeTop,
  NSLayoutAttributeBottom,
  NSLayoutAttributeLeading,
  NSLayoutAttributeTrailing,
  NSLayoutAttributeWidth,
  NSLayoutAttributeHeight,
  NSLayoutAttributeCenterX,
  NSLayoutAttributeCenterY,
  */
  //第三個(gè)參數(shù): 寫零

  //第四個(gè)參數(shù):參照的對(duì)象
  //第五個(gè)參數(shù):與參照對(duì)象的方向
  //第六個(gè)參數(shù):比例,指的是view的寬和高的比例
  //第七個(gè)參數(shù):兩個(gè)視圖的距離
  [self.view addConstraint:[NSLayoutConstraint constraintWithItem:view attribute:NSLayoutAttributeLeft relatedBy:0 toItem:self.view attribute:NSLayoutAttributeLeft multiplier:1 constant:30]];

//確定y軸
[self.view addConstraint:[NSLayoutConstraint constraintWithItem:view attribute:NSLayoutAttributeTop relatedBy:0 toItem:self.view attribute:NSLayoutAttributeTop multiplier:1 constant:30]];

//******* 第一種約束方法 ********
//單獨(dú)給約束對(duì)象寬度，是不需要給參照對(duì)象的；
[self.view addConstraint:[NSLayoutConstraint constraintWithItem:view attribute:NSLayoutAttributeWidth relatedBy:0 toItem:nil attribute:NSLayoutAttributeNotAnAttribute multiplier:1 constant:40]];

//******* 第二種約束方法 *******
//用一個(gè)view的寬度來約束另一個(gè)view的寬度;約束是相互制約的
[self.view addConstraint:[NSLayoutConstraint constraintWithItem:view attribute:NSLayoutAttributeWidth relatedBy:0 toItem:view attribute:NSLayoutAttributeHeight multiplier:1 constant:0]];



UIView *view1 = [[UIView alloc] init];
view1.backgroundColor = [UIColor blueColor];;
[view1 setTranslatesAutoresizingMaskIntoConstraints:NO];
[self.view addSubview:view1];

[self.view addConstraint:[NSLayoutConstraint constraintWithItem:view1 attribute:NSLayoutAttributeLeft relatedBy:0 toItem:view attribute:NSLayoutAttributeRight multiplier:1 constant:40]];

[self.view addConstraint:[NSLayoutConstraint constraintWithItem:view1 attribute:NSLayoutAttributeCenterY relatedBy:0 toItem:view attribute:NSLayoutAttributeCenterY multiplier:1 constant:0]];

[self.view addConstraint:[NSLayoutConstraint constraintWithItem:view1 attribute:NSLayoutAttributeWidth relatedBy:0 toItem:view attribute:NSLayoutAttributeWidth multiplier:1 constant:0]];

[self.view addConstraint:[NSLayoutConstraint constraintWithItem:view1 attribute:NSLayoutAttributeHeight relatedBy:0 toItem:view attribute:NSLayoutAttributeHeight multiplier:1 constant:0]];

}