如何从Swift的字典中获取键的值？

我有一本Swift字典。我想获得钥匙的价值。密钥方法的对象对我不起作用。您如何获得字典键的值？

这是我的字典：

var companies = ["AAPL" : "Apple Inc", "GOOG" : "Google Inc", "AMZN" : "Amazon.com, Inc", "FB" : "Facebook Inc"]

for name in companies.keys { 
    print(companies.objectForKey("AAPL"))
}

使用下标访问字典键的值。这将返回一个可选：

let apple: String? = companies["AAPL"]

要么

if let apple = companies["AAPL"] {
    // ...
}

您还可以枚举所有键和值：

var companies = ["AAPL" : "Apple Inc", "GOOG" : "Google Inc", "AMZN" : "Amazon.com, Inc", "FB" : "Facebook Inc"]

for (key, value) in companies {
    print("\(key) -> \(value)")
}

或枚举所有值：

for value in Array(companies.values) {
    print("\(value)")
}

从Apple Docs

您可以使用下标语法从字典中检索特定键的值。因为可以请求不存在任何值的键，所以字典的下标返回字典值类型的可选值。如果字典中包含所请求键的值，则下标将返回一个可选值，其中包含该键的现有值。否则，下标返回nil：

https://developer.apple.com/documentation/swift/dictionary

if let airportName = airports["DUB"] {
    print("The name of the airport is \(airportName).")
} else {
    print("That airport is not in the airports dictionary.")
}
// prints "The name of the airport is Dublin Airport."