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

Definition

Namespace:

System.Collections.Concurrent

Assemblies:

netstandard.dll, System.Collections.Concurrent.dll

Source:

ConcurrentDictionary.cs

Attempts to add the specified key and value to the ConcurrentDictionary<TKey,TValue>.

C#

public bool TryAdd(TKey key, TValue value);

Parameters

key

TKey

The key of the element to add.

value

TValue

The value of the element to add. The value can be null for reference types.

Returns

Boolean

true if the key/value pair was added to the ConcurrentDictionary<TKey,TValue> successfully; false if the key already exists.

Exceptions

ArgumentNullException

key is null.

OverflowException

The dictionary contains too many elements.

Examples

The following example shows how to call the ConcurrentDictionary<TKey,TValue>.TryAdd 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!");
        }
}

Remarks

This method returns false if the key already exists. Use the TryUpdate or AddOrUpdate method to update the value in case a key already exists.

Applies to

See also

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