更改导航栏的字体

这个问题很简单，但不幸的是答案并非如此。

如何更改文本中的字体UINavigationBar?

从 iOS 7 及更高版本开始：

NSShadow* shadow = [NSShadow new];
shadow.shadowOffset = CGSizeMake(0.0f, 1.0f);
shadow.shadowColor = [UIColor redColor];
[[UINavigationBar appearance] setTitleTextAttributes: @{
     NSForegroundColorAttributeName: [UIColor greenColor],
                NSFontAttributeName: [UIFont fontWithName:@"Helvetica" size:20.0f],
              NSShadowAttributeName: shadow
                                                      }];

从 iOS 5 及更高版本开始：

 [[UINavigationBar appearance] setTitleTextAttributes: @{
                                UITextAttributeTextColor: [UIColor greenColor],
                          UITextAttributeTextShadowColor: [UIColor redColor],
                         UITextAttributeTextShadowOffset: [NSValue valueWithUIOffset:UIOffsetMake(0.0f, 1.0f)],
                                     UITextAttributeFont: [UIFont fontWithName:@"Helvetica" size:20.0f]
     }];

iOS 5 之前：

UILabel *label = [[UILabel alloc] initWithFrame:CGRectMake(0, 0, 400, 44)];
label.backgroundColor = [UIColor clearColor];
label.font = [UIFont boldSystemFontOfSize:20.0];
label.shadowColor = [UIColor colorWithWhite:0.0 alpha:0.5];
label.textAlignment = UITextAlignmentCenter;
label.textColor =[UIColor whiteColor];
label.text=self.title;  
self.navigationItem.titleView = label;      
[label release];