ConcurrentDictionary<TKey,TValue>.TryAdd(TKey, TValue) ConcurrentDictionary<TKey,TValue>.TryAdd(TKey, TValue) ConcurrentDictionary<TKey,TValue>.TryAdd(TKey, TValue) ConcurrentDictionary<TKey,TValue>.TryAdd(TKey, TValue) Method

定義

嘗試將指定的索引鍵和值加入 ConcurrentDictionary<TKey,TValue>Attempts to add the specified key and value to the ConcurrentDictionary<TKey,TValue>.

public:
 bool TryAdd(TKey key, TValue value);
public bool TryAdd (TKey key, TValue value);
member this.TryAdd : 'Key * 'Value -> bool
Public Function TryAdd (key As TKey, value As TValue) As Boolean

參數

key
TKey TKey TKey TKey

要加入的項目的索引鍵。The key of the element to add.

value
TValue TValue TValue TValue

要加入的項目的值。The value of the element to add. 參考類型的值可以是 nullThe value can be null for reference types.

傳回

如果索引鍵/值組已成功加入 true,則為 ConcurrentDictionary<TKey,TValue>;如果索引鍵已經存在,則為 falsetrue if the key/value pair was added to the ConcurrentDictionary<TKey,TValue> successfully; false if the key already exists.

例外狀況

字典已經包含項目數目上限 (MaxValue)。The dictionary already contains the maximum number of elements (MaxValue).

範例

下列範例示範如何呼叫ConcurrentDictionary<TKey,TValue>.TryAdd方法:The following example shows how to call the ConcurrentDictionary<TKey,TValue>.TryAdd method:

class CD_TryXYZ
{
        // Demonstrates:
        //      ConcurrentDictionary<TKey, TValue>.TryAdd()
        //      ConcurrentDictionary<TKey, TValue>.TryUpdate()
        //      ConcurrentDictionary<TKey, TValue>.TryRemove()
        static void Main()
        {
            int numFailures = 0; // for bookkeeping

            // Construct an empty dictionary
            ConcurrentDictionary<int, String> cd = new ConcurrentDictionary<int, string>();

            // This should work
            if (!cd.TryAdd(1, "one"))
            {
                Console.WriteLine("CD.TryAdd() failed when it should have succeeded");
                numFailures++;
            }

            // This shouldn't work -- key 1 is already in use
            if (cd.TryAdd(1, "uno"))
            {
                Console.WriteLine("CD.TryAdd() succeeded when it should have failed");
                numFailures++;
            }

            // Now change the value for key 1 from "one" to "uno" -- should work
            if (!cd.TryUpdate(1, "uno", "one"))
            {
                Console.WriteLine("CD.TryUpdate() failed when it should have succeeded");
                numFailures++;
            }

            // Try to change the value for key 1 from "eine" to "one" 
            //    -- this shouldn't work, because the current value isn't "eine"
            if (cd.TryUpdate(1, "one", "eine"))
            {
                Console.WriteLine("CD.TryUpdate() succeeded when it should have failed");
                numFailures++;
            }

            // Remove key/value for key 1.  Should work.
            string value1;
            if (!cd.TryRemove(1, out value1))
            {
                Console.WriteLine("CD.TryRemove() failed when it should have succeeded");
                numFailures++;
            }

            // Remove key/value for key 1.  Shouldn't work, because I already removed it
            string value2;
            if (cd.TryRemove(1, out value2))
            {
                Console.WriteLine("CD.TryRemove() succeeded when it should have failed");
                numFailures++;
            }

            // If nothing went wrong, say so
            if (numFailures == 0) Console.WriteLine("  OK!");
        }
}
'Imports System.Collections.Concurrent

Class CD_TryXYZ

    ' Demonstrates:
    ' ConcurrentDictionary<TKey, TValue>.TryAdd()
    ' ConcurrentDictionary<TKey, TValue>.TryUpdate()
    ' ConcurrentDictionary<TKey, TValue>.TryRemove()
    Shared Sub Main()
        Dim numFailures As Integer = 0
        ' for bookkeeping
        ' Construct an empty dictionary
        Dim cd As ConcurrentDictionary(Of Integer, [String]) = New ConcurrentDictionary(Of Integer, String)()

        ' This should work
        If Not cd.TryAdd(1, "one") Then
            Console.WriteLine("CD.TryAdd() failed when it should have succeeded")
            numFailures += 1
        End If

        ' This shouldn't work -- key 1 is already in use
        If cd.TryAdd(1, "uno") Then
            Console.WriteLine("CD.TryAdd() succeeded when it should have failed")
            numFailures += 1
        End If

        ' Now change the value for key 1 from "one" to "uno" -- should work
        If Not cd.TryUpdate(1, "uno", "one") Then
            Console.WriteLine("CD.TryUpdate() failed when it should have succeeded")
            numFailures += 1
        End If

        ' Try to change the value for key 1 from "eine" to "one" 
        ' -- this shouldn't work, because the current value isn't "eine"
        If cd.TryUpdate(1, "one", "eine") Then
            Console.WriteLine("CD.TryUpdate() succeeded when it should have failed")
            numFailures += 1
        End If

        ' Remove key/value for key 1. Should work.
        Dim value1 As String = ""
        If Not cd.TryRemove(1, value1) Then
            Console.WriteLine("CD.TryRemove() failed when it should have succeeded")
            numFailures += 1
        End If

        ' Remove key/value for key 1. Shouldn't work, because I already removed it
        Dim value2 As String = ""
        If cd.TryRemove(1, value2) Then
            Console.WriteLine("CD.TryRemove() succeeded when it should have failed")
            numFailures += 1
        End If

        ' If nothing went wrong, say so
        If numFailures = 0 Then
            Console.WriteLine(" OK!")
        End If
    End Sub
End Class

備註

這個方法會傳回false如果索引鍵已經存在。This method returns false if the key already exists. 使用TryUpdateAddOrUpdate方法來更新值,如果索引鍵已存在。Use the TryUpdate or AddOrUpdate method to update the value in case a key already exists.

適用於

另請參閱