backBarButtonItem 替换

最上级vc里面加  下级设置生效

UIImage* image = [UIImage imageNamed:@"back_button.png"];

	[item setBackButtonBackgroundImage:[image resizableImageWithCapInsets:UIEdgeInsetsMake(0, image.size.width, 0, 0)] forState:UIControlStateNormal barMetrics:UIBarMetricsDefault];

	[item setBackButtonTitlePositionAdjustment:UIOffsetMake(-400.f, 0) forBarMetrics:UIBarMetricsDefault];

	self.navigationItem.backBarButtonItem = item;