iOS Swift：无法将值类型“__NSCFNumber”转换为“NSString” [英] iOS Swift: Could not cast value type '__NSCFNumber' to 'NSString'

问题描述

我从我的Firebase数据库（JSON数据库）中检索数字值，然后将这个数字显示到 textField 中，但是当我尝试显示该错误时。

lockquote

无法将值类型'__NSCFNumber'转换为'NSString'

如何正确地将检索到的值转换为一个字符串，并考虑到这个值可能会在字符串和数字之间发生变化。

这是我的代码：

  let quantity = child.childSnapshot（forPath：quantity）。value //从Firebase获取价值
 
 //检查数量是否存在，然后将字符串添加到对象中。 
 if（！（quantity is NSNull）&&（（quantity as！String）！=））{
 newDetail.setQuantity（quantity：quantity as！String）
} 
  

解决方案

错误是说你的数量是 Number ，你不能直接将数字转换为 String ，试试这样。

< pre $ newDetail.setQuantity（quantity：\（quantity））


或

 如果让quantity = child.childSnapshot（forPath：quantity）。value as？ NSNumber {
 newDetail.setQuantity（quantity：quantity.stringValue）
} 
否则如果让quantity = child.childSnapshot（forPath：quantity）。value as？字符串{
 newDetail.setQuantity（quantity：quantity）
} 
  

Single if语句

 如果让数量= child.childSnapshot（forPath：quantity）。value，
（num是NSNumber || num是字符串）{
 newDetail.setQuantity（数量：\（数量））
} 
  

使用第二个和第三个选项不需要检查零。

I am retrieving a number value from my Firebase database (JSON db) and then displaying this number into a textField, although I get this error when I try to display it.

Could not cast value type '__NSCFNumber' to 'NSString'

How can I properly convert the retrieved value to a String, taking into consideration that this value maybe change between a String and a Number when I retrieve it.

Here is my code:

let quantity = child.childSnapshot(forPath: "quantity").value // Get value from Firebase

// Check if the quantity exists, then add to object as string.
if (!(quantity is NSNull) && ((quantity as! String) != "")) {
    newDetail.setQuantity(quantity: quantity as! String)
}

解决方案

The error is saying that your quantity is Number and you cannot directly convert number to String, try like this.

newDetail.setQuantity(quantity: "\(quantity)")

Or

if let quantity = child.childSnapshot(forPath: "quantity").value as? NSNumber {
     newDetail.setQuantity(quantity: quantity.stringValue)
}
else if let quantity = child.childSnapshot(forPath: "quantity").value as? String {
     newDetail.setQuantity(quantity: quantity)
} 

Or With Single if statement

if let quantity = child.childSnapshot(forPath: "quantity").value,
   (num is NSNumber || num is String) {
     newDetail.setQuantity(quantity: "\(quantity))
}

Using second and third option there is no need to check for nil.

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