Ios tab Bar 使用方法

UITabBar* tabBar = [[UITabBar alloc] initWithFrame:CGRectMake(40,0.0,240,30)];

    [mainView addSubview:tabBar];

    [tabBar release];

    

    UITabBarItem *tabBarItem1 = [[UITabBarItem alloc] initWithTitle:@"排队人数" image:nil tag:0];

    UITabBarItem * tabBarItem2 = [[UITabBarItem alloc] initWithTitle:@"人均" image:nil tag:1];

    UITabBarItem * tabBarItem3 = [[UITabBarItem alloc] initWithTitle:@"距离" image:nil tag:2];

    UITabBarItem * tabBarItem4 = [[UITabBarItem alloc] initWithTitle:@"好评" image:nil tag:3];

    NSArray *tabBarItemArray = [[NSArray alloc] initWithObjects: tabBarItem1, tabBarItem2, tabBarItem3, tabBarItem4,nil];

    [tabBar setItems: tabBarItemArray];

    [tabBarItemArray release];

    好像tabBar.backgroundColor = [UIColor blueColor];设置背景不起作用

    alpha可以起作用