IDictionary<TKey,TValue>.Add(TKey, TValue) 方法
重要
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向 IDictionary<TKey,TValue> 添加一个带有所提供的键和值的元素。
public:
void Add(TKey key, TValue value);public void Add (TKey key, TValue value);abstract member Add : 'Key * 'Value -> unitPublic Sub Add (key As TKey, value As TValue)- key
- TKey
用作要添加的元素的键的对象。
- value
- TValue
用作要添加的元素的值的对象。
key 为 null。
IDictionary<TKey,TValue> 中已存在具有相同键的元素。
下面的代码示例使用整数键创建一个空 Dictionary<TKey,TValue> 字符串，并通过 IDictionary<TKey,TValue> 接口访问它。 代码示例使用 Add 方法添加一些元素。 该示例演示方法在 Add 尝试添加重复键时引发 ArgumentException 。
此代码是可以编译和执行的更大示例的一部分。 请参阅 System.Collections.Generic.IDictionary<TKey,TValue>。
// Create a new dictionary of strings, with string keys,
// and access it through the IDictionary generic interface.
IDictionary<String^, String^>^ openWith =
gcnew Dictionary<String^, String^>();
// Add some elements to the dictionary. There are no
// duplicate keys, but some of the values are duplicates.
openWith->Add("txt", "notepad.exe");
openWith->Add("bmp", "paint.exe");
openWith->Add("dib", "paint.exe");
openWith->Add("rtf", "wordpad.exe");
// The Add method throws an exception if the new key is
// already in the dictionary.
try
{
openWith->Add("txt", "winword.exe");
}
catch (ArgumentException^)
{
Console::WriteLine("An element with Key = \"txt\" already exists.");
}
// Create a new dictionary of strings, with string keys,
// and access it through the IDictionary generic interface.
IDictionary<string, string> openWith =
new Dictionary<string, string>();
// Add some elements to the dictionary. There are no
// duplicate keys, but some of the values are duplicates.
openWith.Add("txt", "notepad.exe");
openWith.Add("bmp", "paint.exe");
openWith.Add("dib", "paint.exe");
openWith.Add("rtf", "wordpad.exe");
// The Add method throws an exception if the new key is
// already in the dictionary.
try
{
openWith.Add("txt", "winword.exe");
}
catch (ArgumentException)
{
Console.WriteLine("An element with Key = \"txt\" already exists.");
}
' Create a new dictionary of strings, with string keys,
' and access it through the IDictionary generic interface.
Dim openWith As IDictionary(Of String, String) = _
New Dictionary(Of String, String)
' Add some elements to the dictionary. There are no
' duplicate keys, but some of the values are duplicates.
openWith.Add("txt", "notepad.exe")
openWith.Add("bmp", "paint.exe")
openWith.Add("dib", "paint.exe")
openWith.Add("rtf", "wordpad.exe")
' The Add method throws an exception if the new key is
' already in the dictionary.
Try
openWith.Add("txt", "winword.exe")
Catch
Console.WriteLine("An element with Key = ""txt"" already exists.")
End Try
还可以使用 Item[] 属性通过设置字典中不存在的键的值来添加新元素;例如， myCollection["myNonexistentKey"] = myValue 在 C# (myCollection("myNonexistentKey") = myValue Visual Basic) 。 但是，如果字典中已存在指定的键，则设置 Item[] 属性将覆盖旧值。 相反， Add 方法不修改现有元素。
实现在确定对象相等性的方式上可能会有所不同;例如， List<T> 类使用 Comparer<T>.Default，而 Dictionary<TKey,TValue> 类允许用户指定 IComparer<T> 用于比较键的实现。
实现在是否允许 key 为 null方面可能会有所不同。
| 产品 | 版本 |
|---|---|
| .NET | Core 1.0, Core 1.1, Core 2.0, Core 2.1, Core 2.2, Core 3.0, Core 3.1, 5, 6, 7, 8, 9 |
| .NET Framework | 2.0, 3.0, 3.5, 4.0, 4.5, 4.5.1, 4.5.2, 4.6, 4.6.1, 4.6.2, 4.7, 4.7.1, 4.7.2, 4.8, 4.8.1 |
| .NET Standard | 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 2.0, 2.1 |
| UWP | 10.0 |
