不能下标[AnyObject]的值？索引类型为Int [英] Cannot subscript a value of [AnyObject]? with an index of type Int

问题描述

这是一个扩展首先打开 self.objects ，然后调用它的下标。

---

从Swift 2开始，你也可以使用 guard statement ：

  var user2：PFUser 
 guard let userObject = self.objects？[indexPath.row] else {
 //处理'self.objects'的情况'nil'并退出当前范围
} 
 user2 = userObject as！ PFUser 
  

This is in a class extending PFQueryTableViewController and I am getting the following error. The rows will be PFUser only.
Why am I not able to cast it? Is there a way around this?

The error is:

Cannot subscript a value of [AnyObject]? with an index of type Int

...for this line:

var user2 = self.objects[indexPath.row] as! PFUser

解决方案

The problem isn't the cast, but the fact that self.objects seems to be an optional array: [AnyObject]?.
Therefore, if you want to access one of its values via a subscript, you have to unwrap the array first:

var user2: PFUser
if let userObject = self.objects?[indexPath.row] {
    user2 = userObject as! PFUser
} else {
    //handle the case of 'self.objects' being 'nil'
}

self.objects?[indexPath.row] uses optional chaining to first unwrap self.objects, and then call it's subscript.

---

As of Swift 2, you could also use the guard statement:

var user2: PFUser
guard let userObject = self.objects?[indexPath.row] else {
    //handle the case of 'self.objects' being 'nil' and exit the current scope
}
user2 = userObject as! PFUser

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