将navigationBar的返回按钮的title改为back
很多时候我们使用navigationController时由于上一个navigationController.title的字符串太长，而导致下一个界面的返回按钮变的很长也很难看，为了美观我们我们可以把返回按钮的title改为back，或者是用自定义的图片。

1.把返回按钮的title改为back：这里要特别说明一下，需要在上一个viewController里面写上以下代码。若是在当前viewController中无论你是用self.navigationItem.leftBarButtonItem.title = @"back"; 还是用self.navigationItem.backBarButtonItem.title = @"back"; 都不会修改返回按钮的title。代码如下：

- (void)back:(id)sender {[self.navigationController popViewControllerAnimated:YES];} // The designated initializer.  Override if you create the controller programmatically and want to perform customization that is not appropriate for viewDidLoad.- (id)initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle *)nibBundleOrNil {    if (self = [super initWithNibName:nibNameOrNil bundle:nibBundleOrNil]) {        // 下一个界面的返回按钮UIBarButtonItem *temporaryBarButtonItem = [[UIBarButtonItem alloc] init];temporaryBarButtonItem.title = @"back";temporaryBarButtonItem.target = self;temporaryBarButtonItem.action = @selector(back:);self.navigationItem.backBarButtonItem = temporaryBarButtonItem;[temporaryBarButtonItem release];    }    return self;}

-(IBAction)backAction{[self.navigationController popViewControllerAnimated:YES];} // The designated initializer.  Override if you create the controller programmatically and want to perform customization that is not appropriate for viewDidLoad.- (id)initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle *)nibBundleOrNil {    if (self = [super initWithNibName:nibNameOrNil bundle:nibBundleOrNil]) {        // Custom initializationUIButton *backButton = [UIButton buttonWithType:UIButtonTypeCustom];backButton.frame = CGRectMake(0.0, 0.0, 40.0, 27.0);[backButton setImage:[UIImage imageNamed:@"Btn_Back_Off.png"] forState:UIControlStateNormal];[backButton setImage:[UIImage imageNamed:@"Btn_Back_On.png"] forState:UIControlStateSelected];[backButton addTarget:self action:@selector(backAction) forControlEvents:UIControlEventTouchUpInside];UIBarButtonItem *temporaryBarButtonItem = [[UIBarButtonItem alloc] initWithCustomView:backButton];temporaryBarButtonItem.style = UIBarButtonItemStylePlain;self.navigationItem.leftBarButtonItem=temporaryBarButtonItem;[temporaryBarButtonItem release];    }    return self;}