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

定義

命名空間:

System.Collections.Generic

組件:

System.Collections.dll

來源:

SortedList.cs

取得與指定索引鍵關聯的值。

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

參數

key

TKey

要取得其值的索引鍵。

value

TValue

這個方法傳回時，如果找到索引鍵，則為與指定索引鍵關聯的值，否則為 value 參數的型別預設值。 這個參數會以未初始化的狀態傳遞。

傳回

Boolean

如果 true 包含具有指定索引鍵的項目，則為 SortedList<TKey,TValue>，否則為 false。

實作

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

例外狀況

ArgumentNullException

key 為 null。

範例

此範例示範如何使用 TryGetValue 方法作為更有效率的方式，以擷取程式中經常嘗試不在排序列表中的索引鍵的值。 相反地，此範例也會示範屬性如何 Item[] (C# ) 嘗試擷取不存在的索引鍵時擲回例外狀況。

此程式代碼範例是針對 類別提供的較大範例的 SortedList<TKey,TValue> 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."

備註

這個方法結合了 方法和 Item[] 屬性的功能ContainsKey。

如果找不到索引鍵，則 value 參數會取得實值型 TValue別的適當預設值;例如，整數類型的零 (0) 、 false 布爾類型，以及 null 參考型別。

這個方法會執行二進位搜尋;因此，這個方法是 O (記錄 n) 作業，其中 n 是 Count。

另請參閱

• ContainsKey(TKey)
• Item[TKey]
• ContainsValue(TValue)
• IndexOfValue(TValue)