ios - 预期返回 'Int' 的函数中缺少返回值

Question

func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int
{
    canvasCount { (value) in
        if let res = value {
            return res
        }
    } //Missing return in a closure expected to return 'Int'
} //Missing return in a closure expected to return 'Int'

Missing return in a closure expected to return 'Int'

func canvasCount(completion:@escaping((_ va:Int?) -> Int )) {

    ref.child("Canvas").observeSingleEvent(of: .value, with: { (snapshot) in
        completion( snapshot.children.allObjects.count)
    }) { (error) in
        print(error.localizedDescription)
        completion(nil)
    }

}

您好，我希望能够以整数形式返回 snapshot.children.allObjects.count。但是我用 canvasCount 函数得到了这个错误“在一个期望返回‘Int’的闭包中缺少返回”。任何人都可以帮助我吗？

Answer 1

您需要完成，因为对 firebase 的调用是异步的

func canvasCount(completion:@escaping((_ va:Int?) -> () )) { 

    ref.child("Canvas").observeSingleEvent(of: .value, with: { (snapshot) in
           completion( snapshot.children.allObjects.count)
    }) { (error) in
        print(error.localizedDescription)
           completion(nil)
    }

}

---

canvasCount { (value) in 
   if let res = value {
      print(res)
   }
}

编辑 ------------------------------------ ----------

声明一个实例变量

var counter = 0

在 viewDidLoad 内插入

canvasCount { (value) in
  if let res = value {
     self.counter =  res
     self.tableView.reloadData()
  }
} 

然后复制那些

func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int
{
    return counter
} 


func canvasCount(completion:@escaping((_ va:Int?) -> ())) {

    ref.child("Canvas").observeSingleEvent(of: .value, with: { (snapshot) in
        completion( snapshot.children.allObjects.count)
    }) { (error) in
        print(error.localizedDescription)
        completion(nil)
    }

}