iOS Swift: Could not cast value type '__NSCFNumber' to 'NSString'
<p>I am retrieving a number value from my Firebase database (JSON db) and then displaying this number into a <code>textField</code>, although I get this error when I try to display it.</p>

<blockquote>
  <p>Could not cast value type '__NSCFNumber' to 'NSString'</p>
</blockquote>

<p>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.</p>

<p>Here is my code:</p>

<pre><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) &amp;&amp; ((quantity as! String) != "")) {
    newDetail.setQuantity(quantity: quantity as! String)
}
</code></pre>