iOS中navigationItem的titleView如何居中

//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(0, 0, 320, 44)];

    // 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(0, 0, 320, 44)];

    titleLabel.tag = kUIVIEWCONTROLLER_LABEL_TAG;

    titleLabel.backgroundColor = [UIColor clearColor];

    titleLabel.font = [UIFont fontWithName:@"Helvetica-Bold" size:16];

    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 += 15;//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 = 320 - maxWidth * 2;

    titleLabel.frame = frame;



    frame = titleView.frame;

    frame.size.width = 320 - maxWidth * 2;

    titleView.frame = frame;

    // Set the text

    titleLabel.text = text;

        // Add as the nav bar‘s titleview

    [titleView addSubview:titleLabel];

    self.navigationItem.titleView = titleView;

}