@implementation AppDelegate

– (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
    self.window = [[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds]];
   
    self.window.backgroundColor = [UIColor whiteColor];
    [self.window makeKeyAndVisible];
    ViewController1 *v1=[[ViewController1 alloc]init];
    UINavigationController *navation=[[UINavigationController alloc]initWithRootViewController:v1];
    navation.title=@”首页”;
    ViewController2 *v2=[[ViewController2 alloc]init];
    UITabBarItem *item2=[[UITabBarItem alloc]initWithTabBarSystemItem:UITabBarSystemItemBookmarks tag:1];
    v2.tabBarItem=item2;
   
     ViewController3 *v3=[[ViewController3 alloc]init];
      UITabBarItem *item3=[[UITabBarItem alloc]initWithTabBarSystemItem:UITabBarSystemItemBookmarks tag:2];
    v3.tabBarItem=item3;
    NSArray *viewcontrols=[[NSArray alloc]initWithObjects:navation,v2,v3,nil];
    UITabBarController *tabcotrollers=[[UITabBarController alloc]init];
  
    tabcotrollers.selectedViewController=v2;
    tabcotrollers.tabBar.tintColor=[UIColor greenColor];
    tabcotrollers.viewControllers=viewcontrols;
    self.window.rootViewController=tabcotrollers;

错误如下：

Terminating app due to uncaught exception “”NSInvalidArgumentException””, reason: “”-[UITabBarController setSelectedViewController:] only a view controller in the tab bar controller””s list of view controllers can be selected.””
*** First throw call stack:
(
0   CoreFoundation                      0x017ee1e4 __exceptionPreprocess + 180
1   libobjc.A.dylib                     0x0156d8e5 objc_exception_throw + 44
2   CoreFoundation                      0x017edfbb +[NSException raise:format:] + 139
3   UIKit                               0x0037facc -[UITabBarController setSelectedViewController:] + 180
4   UItabBarItem                        0x00002d39 -[AppDelegate application:didFinishLaunchingWithOptions:] + 1241
5   UIKit                               0x0022714f -[UIApplication _handleDelegateCallbacksWithOptions:isSuspended:restoreState:] + 309
6   UIKit                               0x00227aa1 -[UIApplication _callInitializationDelegatesForURL:payload:suspended:] + 1810
7   UIKit                               0x0022c667 -[UIApplication _runWithURL:payload:launchOrientation:statusBarStyle:statusBarHidden:] + 824
8   UIKit                               0x00240f92 -[UIApplication handleEvent:withNewEvent:] + 3517
9   UIKit                               0x00241555 -[UIApplication sendEvent:] + 85
10  UIKit                               0x0022e250 _UIApplicationHandleEvent + 683
11  GraphicsServices                    0x037e3f02 _PurpleEventCallback + 776
12  GraphicsServices                    0x037e3a0d PurpleEventCallback + 46
13  CoreFoundation                      0x01769ca5 __CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE1_PERFORM_FUNCTION__ + 53
14  CoreFoundation                      0x017699db __CFRunLoopDoSource1 + 523
15  CoreFoundation                      0x0179468c __CFRunLoopRun + 2156
16  CoreFoundation                      0x017939d3 CFRunLoopRunSpecific + 467
17  CoreFoundation                      0x017937eb CFRunLoopRunInMode + 123
18  UIKit                               0x0022bd9c -[UIApplication _run] + 840
19  UIKit                               0x0022df9b UIApplicationMain + 1225
20  UItabBarItem                        0x000037cd main + 141
21  libdyld.dylib                       0x01e35701 start + 1
)
libc++abi.dylib: terminating with uncaught exception of type NSException

这个该怎么破？（xcode5.1 ios7的配置）