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

定义

尝试将指定的键和值添加到 ConcurrentDictionary<TKey,TValue> 中。 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
参数
key
TKey TKey TKey TKey

要添加的元素的键。 The key of the element to add.

value
TValue TValue TValue TValue

要添加的元素的值。 The value of the element to add. 对于引用类型,该值可以为 null The value can be null for reference types.

返回

如果该键/值对已成功添加到 ConcurrentDictionary<TKey,TValue>,则为 true;如果该键已存在,则为 false true if the key/value pair was added to the ConcurrentDictionary<TKey,TValue> successfully; false if the key already exists.

异常

字典中已包含元素的最大数量(MaxValue)。 The dictionary already contains the maximum number of elements (MaxValue).

示例

下面的示例演示如何调用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

注解

此方法返回false如果该键已存在。This method returns false if the key already exists. 使用TryUpdateAddOrUpdate方法来更新的值,如果键已存在。Use the TryUpdate or AddOrUpdate method to update the value in case a key already exists.

适用于

另请参阅