错误是说您的数量是Number，您不能直接将数字转换为String，尝试这样。
newDetail.setQuantity(quantity: "\(quantity)")
要么
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)
}
或使用单if语句
if let quantity = child.childSnapshot(forPath: "quantity").value,
(num is NSNumber || num is String) {
newDetail.setQuantity(quantity: "\(quantity))
}
使用第二和第三个选项，无需检查nil。
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