tabbar显示原图

nav.tabBarItem.image = [[UIImage imageNamed:tabBarIcons[i]] imageWithRenderingMode:UIImageRenderingModeAlwaysOriginal];nav.tabBarItem.selectedImage = [[UIImage imageNamed:[NSString stringWithFormat:@"%@_down",tabBarIcons[i]]]imageWithRenderingMode:UIImageRenderingModeAlwaysOriginal];