iOS 使用代码创建约束,实现自动布局

///与下面约束对象属性截图相对应
//使用Auto Layout约束，禁止将Autoresizing Mask转换为约束
[self.funcView setTranslatesAutoresizingMaskIntoConstraints:NO];
/**
*@1.constraintWithItem:你想要约束的视图
*@2.attribute:约束的属性(枚举值,可使用com键查看)
*@3.relatedBy:与约束的父视图的关系(枚举值)
*@4.toItem:约束对象的父视图
*@5.attribute:约束的属性(枚举值,可使用com键查看),一般情况下与第二个参数写一样的
*@6.multiplier:相对于父视图的约束比例
*@7.constant:约束间隔
*/
  //与约束视图与父视图宽度一致
  NSLayoutConstraint *w = [NSLayoutConstraint constraintWithItem:_funcView attribute:NSLayoutAttributeWidth relatedBy:NSLayoutRelationEqual toItem:_fview attribute:NSLayoutAttributeWidth multiplier:1 constant:0];
//与约束视图与父视图高度一致
  NSLayoutConstraint *h = [NSLayoutConstraint constraintWithItem:_funcView attribute:NSLayoutAttributeHeight relatedBy:NSLayoutRelationEqual toItem:_fview attribute:NSLayoutAttributeHeight multiplier:1 constant:0];
 //与约束视图与父视图center.x一致
  NSLayoutConstraint *x = [NSLayoutConstraint constraintWithItem:_funcView attribute:NSLayoutAttributeCenterX relatedBy:NSLayoutRelationEqual toItem:_fview attribute:NSLayoutAttributeCenterX multiplier:1 constant:0];
 //与约束视图与父视图center.y一致
  NSLayoutConstraint *y = [NSLayoutConstraint constraintWithItem:_funcView attribute:NSLayoutAttributeCenterY relatedBy:NSLayoutRelationEqual toItem:_fview attribute:NSLayoutAttributeCenterY multiplier:1 constant:0];

  //把约束添加到父视图上
  NSArray *array = @[w,h,x,y];
  [_fview addConstraints:array];