设置UINavigation标题

先前给UINavigation添加图片成功，后来添加标题：

self.title=@"Activity";

没显示任何内容。

我用另一种方法添加标题标签，在第一个视图控制器运行成功，但是在第二个视图控制器修改标题后还是显示先前的标题。

代码:

UIImage *image = [UIImage imageNamed:@"Nav.png"];
UIImageView *imageView = [[UIImageView alloc] initWithImage:image];
[self.navigationController.navigationBar addSubview:imageView]; 
   titleLabel=[[UILabel alloc] initWithFrame:CGRectMake(50,2,250,36)];
     titleLabel.text=@"Activity";
titleLabel.textColor=[UIColor whiteColor];
titleLabel.backgroundColor=[UIColor clearColor];
titleLabel.font=[UIFont fontWithName:@"Helvetica-Bold" size :18];
//titleLabel boldSystemFontOfSize:14.0;
[self.navigationController.navigationBar addSubview:titleLabel];

if ([navBar respondsToSelector:@selector(setBackgroundImage:forBarMetrics:)])
{
    [navBar setBackgroundImage:[UIImage imageNamed:@"Nav.png"] forBarMetrics:UIBarMetricsDefault];
}
else
{
    UIImageView *imageView = (UIImageView *)[navBar viewWithTag:1];//any tag
    if (imageView == nil)
    {
        imageView = [[UIImageView alloc] initWithImage:
                    [UIImage imageNamed:@"Nav.png"]];
        [navBar insertSubview:imageView atIndex:0];
        [imageView release];
    }
}
self.title=@"Activity";

用我的代码试试吧