TryAdd Method

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

.NET Framework (current version)
 

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

Namespace:   System.Collections.Concurrent
Assembly:  mscorlib (in mscorlib.dll)

public bool TryAdd(
	TKey key,
	TValue value
)

Parameters

key
Type: TKey

The key of the element to add.

value
Type: TValue

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

Return Value

Type: System.Boolean

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

Exception Condition
ArgumentNullException

key is null.

OverflowException

The dictionary already contains the maximum number of elements (MaxValue).

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.

The following example shows how to call the ConcurrentDictionary<TKey, TValue>.TryAddmethod:

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!");
        }
}

Universal Windows Platform
Available since 8
.NET Framework
Available since 4.0
Portable Class Library
Supported in: portable .NET platforms
Windows Phone
Available since 8.1
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