判断是否打开了相机

 NSString *mediaType = AVMediaTypeVideo;//读取媒体类型

    AVAuthorizationStatus authStatus = [AVCaptureDevice authorizationStatusForMediaType:mediaType];//读取设备授权状态

    if(authStatus == AVAuthorizationStatusRestricted || authStatus == AVAuthorizationStatusDenied){

        UIAlertView * alert = [[UIAlertView alloc]initWithTitle:@"无法拍照" message:@"请在iPhone的“设置-隐私-相机”选项中，允许觅星访问你的手机相机" delegate:self cancelButtonTitle:@"ok" otherButtonTitles:nil, nil];

        [alert show];

        return;

    }