SortedList<TKey,TValue>.TryGetValue(TKey, TValue) 方法

定义

命名空间:
System.Collections.Generic
程序集:
System.dll, System.Collections.dll
程序集:
System.dll
程序集:
System.Collections.dll
程序集:
netstandard.dll

获取与指定键关联的值。

public:
 virtual bool TryGetValue(TKey key, [Runtime::InteropServices::Out] TValue % value);
public bool TryGetValue(TKey key, out TValue value);
abstract member TryGetValue : 'Key * 'Value -> bool
override this.TryGetValue : 'Key * 'Value -> bool
Public Function TryGetValue (key As TKey, ByRef value As TValue) As Boolean

参数

key
TKey

要获取其值的键。

value
TValue

此方法返回时，如果找到该键，则与指定键关联的值;否则为参数类型的 value 默认值。 此参数未初始化传递。

返回

Boolean

true 如果包含具有指定键的元素，则为 SortedList<TKey,TValue> ;否则为 false。

实现

TryGetValue(TKey, TValue) TryGetValue(TKey, TValue)

例外

ArgumentNullException

key 是 null。

示例

该示例演示如何将 TryGetValue 该方法用作更高效的方法，以检索经常尝试不在排序列表中的键的程序中的值。 相反，该示例还演示了尝试检索不存在的键时属性（C# 中的索引器）如何 Item[] 引发异常。

该代码示例是 SortedList<TKey,TValue> 类中的一个较大示例的一部分。

// When a program often has to try keys that turn out not to
// be in the list, TryGetValue can be a more efficient
// way to retrieve values.
string value = "";
if (openWith.TryGetValue("tif", out value))
{
    Console.WriteLine("For key = \"tif\", value = {0}.", value);
}
else
{
    Console.WriteLine("Key = \"tif\" is not found.");
}

' When a program often has to try keys that turn out not to
' be in the list, TryGetValue can be a more efficient 
' way to retrieve values.
Dim value As String = ""
If openWith.TryGetValue("tif", value) Then
    Console.WriteLine("For key = ""tif"", value = {0}.", value)
Else
    Console.WriteLine("Key = ""tif"" is not found.")
End If

// When a program often has to try keys that turn out not to
// be in the list, TryGetValue can be a more efficient
// way to retrieve values.
match openWith.TryGetValue("tif") with
| true, value ->
    printfn "For key = \"tif\", value = {value}."
| false, _ ->
    printfn "Key = \"tif\" is not found."

// The indexer throws an exception if the requested key is
// not in the list.
try
{
    Console.WriteLine("For key = \"tif\", value = {0}.",
        openWith["tif"]);
}
catch (KeyNotFoundException)
{
    Console.WriteLine("Key = \"tif\" is not found.");
}

' The default Item property throws an exception if the requested
' key is not in the list.
Try
    Console.WriteLine("For key = ""tif"", value = {0}.", _
        openWith("tif"))
Catch 
    Console.WriteLine("Key = ""tif"" is not found.")
End Try

// The indexer throws an exception if the requested key is
// not in the list.
try
    printfn $"""For key = "tif", value = {openWith["tif"]}."""
with 
    | :? KeyNotFoundException ->
        printfn "Key = \"tif\" is not found."

注解

此方法结合了该方法和Item[]属性的功能ContainsKey。

如果未找到键，则 value 参数将获取值类型的相应默认值;例如，整数类型的 TValue零（0）、 false 布尔类型以及 null 引用类型。

此方法执行二进制搜索;因此，此方法是 O（logn） 操作，其中 n 。Count

适用于

另请参阅