ConcurrentDictionary<TKey,TValue>.TryUpdate Method

Definition

Namespace:

System.Collections.Concurrent

Assemblies:

netstandard.dll, System.Collections.Concurrent.dll

Source:

ConcurrentDictionary.cs

Updates the value associated with key to newValue if the existing value with key is equal to comparisonValue.

C#

public bool TryUpdate(TKey key, TValue newValue, TValue comparisonValue);

Parameters

key

TKey

The key of the value that is compared with comparisonValue and possibly replaced.

newValue

TValue

The value that replaces the value of the element that has the specified key if the comparison results in equality.

comparisonValue

TValue

The value that is compared with the value of the element that has the specified key.

Returns

Boolean

true if the value with key was equal to comparisonValue and was replaced with newValue; otherwise, false.

Exceptions

ArgumentNullException

key is null.

Examples

The following example shows how to call the TryUpdate method:

C#

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!");
        }
}

Applies to

See also

• Thread-Safe Collections
• How to: Add and Remove Items from a ConcurrentDictionary