使用代码为ib里面的控件添加布局约束无效

// ViewController.m
// LayoutEx
//
// Created by Thinkpad on 15/5/14.
// Copyright (c) 2015年 Exia.Guo. All rights reserved.
//

#import "ViewController.h"
#import "AutoLayout+Assist.h"

@interface ViewController ()
@property (weak, nonatomic) IBOutlet UILabel *rootLabel;
@property (nonatomic,strong) IBOutlet UIView *rootView;
@end

@implementation ViewController

• (void)viewDidLoad {
  [super viewDidLoad];
  [self.rootView addSubview:self.rootLabel];
  }

• (void)didReceiveMemoryWarning {
  [super didReceiveMemoryWarning];
  // Dispose of any resources that can be recreated.
  }

-(void)updateViewConstraints{
[super updateViewConstraints];
UILabel* label = (UILabel*)[self.view viewWithTag:8080];

label.translatesAutoresizingMaskIntoConstraints = NO;

NSLog(@"DO UPDATE VIEW CONSTRAINTS");

NSLayoutConstraint* labelRootConstraint1 = [NSLayoutConstraint constraintWithItem:label attribute:NSLayoutAttributeCenterX relatedBy:NSLayoutRelationEqual toItem:self.view attribute:NSLayoutAttributeCenterX multiplier:1 constant:0];
NSLayoutConstraint* labelRootConstraint2 = [NSLayoutConstraint constraintWithItem:label attribute:NSLayoutAttributeCenterY relatedBy:NSLayoutRelationEqual toItem:self.view attribute:NSLayoutAttributeCenterY multiplier:1 constant:0];

[labelRootConstraint1 install:780];
[labelRootConstraint2 install:780];

}

@end

上面的代码添加成功了，xcode控制台也没有错误输出，但是在启动的时候就是没用中心对其的效果，这个是为什么呢？
这个好无语，希望大家遇到同样问题的解答一下我的疑惑，谢谢

• (void)performSelector:(SEL)aSelector withObject:(nullable id)anArgument afterDelay:(NSTimeInterval)delay; 你用这个方法延迟更新下约束就好