                 //如果json文件动态加载控制器出错，则默认为本地创建
                 addChildViewController("HomeTableViewController", title: "首页", imageName: "tabbar_home")
                 addChildViewController("MessageTableViewController", title: "消息", imageName: "tabbar_message_center")
+                
+                //添加一个占位控制器
+                addChildViewController("NullViewController", title: "", imageName: "")
+                
                 addChildViewController("DiscoverTableViewController", title: "广场", imageName: "tabbar_discover")
                 addChildViewController("ProfileTableViewController", title: "我", imageName: "tabbar_profile")
             }
         }
-        
     }
+    
     /**
      初始化子控制器
      

        
        tabBar.tintColor = UIColor.orangeColor()
        
        //获取json文件路径（可以通过服务器更改控制器数据）
        let path = NSBundle.mainBundle().pathForResource("MainVCSettings.json", ofType: nil)
        //通过文件路径创建NSData

        
        addChildViewController(nav)
    }
    
    //MARK: - 懒加载
    private lazy var composeBtn:UIButton = {
        
        let btn = UIButton()
        //添加前景图片
        btn.setImage(UIImage(named: "tabbar_compose_icon_add"), forState: UIControlState.Normal)
        btn.setImage(UIImage(named: "tabbar_compose_icon_add_highlighted"), forState: UIControlState.Highlighted)
        //添加背景图片
        btn.setBackgroundImage(UIImage(named: "tabbar_compose_button"), forState: UIControlState.Normal)
        btn.setBackgroundImage(UIImage(named: "tabbar_compose_button_highlighted"), forState: UIControlState.Highlighted)
        
        btn.addTarget(self, action: "composeBtnClick", forControlEvents: UIControlEvents.TouchUpInside)
        
        return btn
    }()

}
