[[UIBarButtonItem appearance] setBackButtonTitlePositionAdjustment:UIOffsetMake(0, -60)forBarMetrics:UIBarMetricsDefault];
将文字偏移出屏幕，这种方式会导致返回箭头偏下，最好还是自己自定义。
//是否使用默认的导航栏左右按钮
@property (nonatomic, assign, getter=isUsingDefaultLeftNaviButton) BOOL usingDefaultLeftNaviButton;
@property (nonatomic, assign, getter=isUsingDefaultRightNaviButton) BOOL usingDefaultRightNaviButton;
if (self.isUsingDefaultLeftNaviButton)
{
UIButton *leftButton = [UIButton buttonWithType:UIButtonTypeCustom];
[leftButton setImage:[UIImage imageNamed:@"navback_black"] forState:UIControlStateNormal];
[leftButton setImage:[UIImage imageNamed:@"navback_black"] forState:UIControlStateHighlighted];
[leftButton addTarget:self action:@selector(leftNaviButtonAction:) forControlEvents:UIControlEventTouchUpInside];
leftButton.frame = CGRectMake(0, 0, 44, 44);
leftButton.contentHorizontalAlignment = UIControlContentHorizontalAlignmentLeft;
UIBarButtonItem *leftItem = [[UIBarButtonItem alloc] initWithCustomView:leftButton];
self.navigationItem.leftBarButtonItem = leftItem;
}
