怎么设置UIBarButtonItem的背景图片？

UIBarButtonItem *rightButtonItem=[[UIBarButtonItem alloc] initWithImage:[UIImage imageNamed:@"main_right_nav"] style:UIBarButtonItemStylePlain target:self action:@selector(selectRightAction:)];//1
[rightButtonItem setTintColor:[UIColor colorWithPatternImage:[UIImage imageNamed:@"main_right_nav"]]];//2

为什么只有第一句的情况下rightButtonItem的背景图片显示不出来？必须有第二句才能成功设置rightButtonItem的背景图片的背景图片么？

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这样就可以吧
iOS7后面

UIImage *image = [[UIImage imageNamed:@"myImage.png"] imageWithRenderingMode:UIImageRenderingModeAlwaysOriginal];
UIBarButtonItem *button = [[UIBarButtonItem alloc] initWithImage:image 
            style:UIBarButtonItemStylePlain 
            target:self 
            action:@selector(YOUR_METHOD:)];