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

  • 参考

定义

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

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

当此方法返回时，如果找到指定键，则返回与该键相关联的值；否则，将返回 value 参数的类型的默认值。 此参数未经初始化即被传递。

返回

Boolean

如果 true 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 为 null。

示例

该示例演示如何使用 TryGetValue 方法作为一种更有效的方法来检索经常尝试不在排序列表中的键的程序中的值。 相比之下，该示例还演示了属性 (C#) 在尝试检索不存在的键时如何 Item[] 引发异常。

此代码示例是为 SortedList<TKey,TValue> 类提供的一个更大示例的一部分。

// 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", 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.
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 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 方法和 Item[] 属性的功能ContainsKey。

如果未找到该键，则value参数将获取值类型的相应默认值;例如，对于整数类型TValue，为零 (0) ，false对于布尔类型，对于引用类型。null

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

适用于

另请参阅