iOS to determine if Bluetooth is turned on

In doing ibeacon module, first of all to determine whether the Bluetooth is open. So the question is, how to use code to determine the Bluetooth open.
Check the API, found that Cbcentralmanager can be implemented.

The first step is to complete the protocol Cbcentralmanagerdelegate

@property Cbcentralmanager *centralmanager;

Self.centralmanager = [[Cbcentralmanager alloc] initwithdelegate:self queue:nil Options:nil];

-(void) Centralmanagerdidupdatestate: (Cbcentralmanager *)
    The first time you turn on or every Bluetooth state change will call this function
    if ( Central.state==cbcentralmanagerstatepoweredon)
    {
        NSLog (@ "Bluetooth device Open");
        _canshake=yes;
    }
    else
    {
        NSLog (@ "Bluetooth device is off");

        Uialertview *alterview=[[uialertview alloc]initwithtitle:@ "Pro, please turn on Bluetooth Oh" message:@ "turn on Bluetooth shake, the discount will appear Oh ~" Delegate:self cancelbuttontitle:@ "Okay. "Otherbuttontitles:nil];
        [Alterview show];
        _canshake=no
    }
}