控件不显示

 UIView *indicateView = [[UIView alloc]initWithFrame:CGRectMake(0, 33, 20, 2)];
    indicateView.backgroundColor = [UIColor redColor];
    self.indicatorView = indicateView;
   
    //子选项
    CGFloat width = self.view.width / 5;
    for (int i = 0; i < self.titles.count; i++) {
        
        UIButton *tap = [UIButton buttonWithType:UIButtonTypeCustom];
        tap.tag = i;
        tap.backgroundColor = kRandomColor;
        tap.frame = CGRectMake(i * width, 0, width, 35);
        [tap setTitle:self.titles[i] forState:UIControlStateNormal];
        [tap setTitleColor:[UIColor grayColor] forState:UIControlStateNormal];
        [tap addTarget:self action:@selector(tap:) forControlEvents:UIControlEventTouchUpInside];
        [titleView addSubview:tap];
        
        if (i == 0) {
            tap.titleLabel.backgroundColor = [UIColor yellowColor];
            //[tap.titleLabel sizeToFit];
            //[tap layoutIfNeeded];
            NSLog(@"%f,%f",tap.titleLabel.width,tap.centerX);
            self.indicatorView.width = tap.titleLabel.width; //原因在这句，此时tap.titleLabel.width = 0,所以要强制布局，用sizeToFit或layoutIfNeeded
           self.indicatorView.centerX = tap.centerX;
            
        }
    }

控件创建出来设置了frame,在某处用了该控件的尺寸，但是系统也许在这个时候还没有计算该控件的尺寸什么的，所以这个时候就要强制系统计算布局。