开发过程中，发现titleview很难居中，通过各种尝试终于找到了解决方法。
首先清楚你个概念：
leftBarButtonItem，导航条中左侧button。
rightBarButtonItem，导航条中右侧button。
titleview，不用介绍了吧，就是标题。
问题原因：
经过尝试，发现titleview的起点位置和尺寸依赖于leftBarButtonItem和rightBarButtonItem的位置。
解决方案：
设置titleview之前，先初始化leftBarButtonItem和rightBarButtonItem的位置，然后根据leftBarButtonItem和rightBarButtonItem的位置来使titleview居中。
//以下使参考代码。
//必须放在 leftBarButtonItem和rightBarButtonItem初始化之后调用
- (void)setDisplayCustomTitleText:(NSString*)text
{
// Init views with rects with height and y pos
UIView *titleView = [[UIView alloc] initWithFrame:CGRectMake(, , , )];
// Use autoresizing to restrict the bounds to the area that the titleview allows
titleView.autoresizingMask = UIViewAutoresizingFlexibleWidth | UIViewAutoresizingFlexibleLeftMargin | UIViewAutoresizingFlexibleRightMargin;
titleView.autoresizesSubviews = YES;
titleView.backgroundColor = [UIColorclearColor];
UILabel *titleLabel = [[UILabel alloc] initWithFrame:CGRectMake(, , , )];
titleLabel.tag = kUIVIEWCONTROLLER_LABEL_TAG;
titleLabel.backgroundColor = [UIColor clearColor];
titleLabel.font = [UIFont fontWithName:@"Helvetica-Bold" size:];
titleLabel.textAlignment = UITextAlignmentCenter;
titleLabel.autoresizingMask = UIViewAutoresizingFlexibleWidth | UIViewAutoresizingFlexibleHeight;
titleLabel.textColor = TC_CNavigationTitleColor;
titleLabel.lineBreakMode = UILineBreakModeClip;
titleLabel.textAlignment = UITextAlignmentCenter;
titleLabel.autoresizingMask = titleView.autoresizingMask;
CGRect leftViewbounds = self.navigationItem.leftBarButtonItem.customView.bounds;
CGRect rightViewbounds = self.navigationItem.rightBarButtonItem.customView.bounds;
CGRect frame;
CGFloat maxWidth = leftViewbounds.size.width > rightViewbounds.size.width ? leftViewbounds.size.width : rightViewbounds.size.width;
maxWidth += ;//leftview 左右都有间隙，左边是5像素，右边是8像素，加2个像素的阀值 5 ＋ 8 ＋ 2
frame = titleLabel.frame;
frame.size.width = - maxWidth * ;
titleLabel.frame = frame;
frame = titleView.frame;
frame.size.width = - maxWidth * ;
titleView.frame = frame;
// Set the text
titleLabel.text = text;
// Add as the nav bar's titleview
[titleView addSubview:titleLabel];
self.navigationItem.titleView = titleView;
}