IOS tabbar用法

-(void)initBottom{
UITabBar* tabBar=[[UITabBar alloc] initWithFrame:CGRectMake(0,self.view.frame.size.height-64-tabHeight, self.view.frame.size.width, tabHeight)];

[tabBar setBackgroundColor:[UIColor colorWithHexString:@""]];
UITabBarItem *tabBar0=[[UITabBarItem alloc] init];
UIImage *image0          = [[UIImage imageNamed:@"mainContract.png"] imageWithRenderingMode:UIImageRenderingModeAlwaysOriginal];
UIImage *selectedImage0  = [[UIImage imageNamed:@"mainContractSelect.png"] imageWithRenderingMode:UIImageRenderingModeAlwaysOriginal];
UIOffset offset;
offset.horizontal=0;
offset.vertical=-5;
tabBar0.image   = image0;
tabBar0.selectedImage = selectedImage0;
tabBar0.title=@"第一个Item";
tabBar0.tag=0;
tabBar0.titlePositionAdjustment=offset;

UITabBarItem *tabBar1=[[UITabBarItem alloc] init];
UIImage *image1          = [[UIImage imageNamed:@"market.png"] imageWithRenderingMode:UIImageRenderingModeAlwaysOriginal];
UIImage *selectedImage1  = [[UIImage imageNamed:@"marketSelect.png"] imageWithRenderingMode:UIImageRenderingModeAlwaysOriginal];
tabBar1.image   = image1;
tabBar1.tag=1;
tabBar1.selectedImage = selectedImage1;
tabBar1.title=@"<span style="font-family: Arial, Helvetica, sans-serif;">第二个Item</span>";
tabBar1.titlePositionAdjustment=offset;

UITabBarItem *tabBar2=[[UITabBarItem alloc] init];
UIImage *image2          = [[UIImage imageNamed:@"calculate.png"] imageWithRenderingMode:UIImageRenderingModeAlwaysOriginal];
UIImage *selectedImage2  = [[UIImage imageNamed:@"calculateSelect.png"] imageWithRenderingMode:UIImageRenderingModeAlwaysOriginal];
tabBar2.image   = image2;
tabBar2.selectedImage = selectedImage2;
tabBar2.tag=2;
tabBar2.title=@"<span style="font-family: Arial, Helvetica, sans-serif;">第三个Item</span>";
tabBar2.titlePositionAdjustment=offset;
NSArray *items=[[NSArray alloc] initWithObjects:tabBar0,tabBar1,tabBar2, nil];
[tabBar setItems:items];
tabBar.delegate=self;
[self.view addSubview:tabBar];
self.markView=[[UIView alloc] initWithFrame:CGRectMake(0, self.view.frame.size.height-64-2*tabHeight, self.view.frame.size.width, tabHeight)];
[self.markView setBackgroundColor:[UIColor greenColor]];
[self.view addSubview:self.markView];

}