將返回按鈕的樣式改為自己的圖片，這樣能夠保留系統(tǒng)的返回手勢(shì)基公。
UIImage *backImage = [UIImage imageNamed:@"backNor"];
[[UIBarButtonItem appearance] setBackButtonBackgroundImage:[backImage resizableImageWithCapInsets:UIEdgeInsetsMake(0, backImage.size.width, 0, 0)]
forState:UIControlStateNormal barMetrics:UIBarMetricsDefault];
[[UIBarButtonItem appearance] setBackButtonTitlePositionAdjustment:UIOffsetMake(-233, 0) forBarMetrics:UIBarMetricsDefault];
