ConcurrentDictionary<TKey,TValue>.TryAdd(TKey, TValue) Method
Definition
Important
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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
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
true
if the key/value pair was added to the ConcurrentDictionary<TKey,TValue> successfully; false
if the key already exists.
Exceptions
key
is null
.
The dictionary contains too many elements.
Examples
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!");
}
}
// Demonstrates:
// ConcurrentDictionary<TKey, TValue>.TryAdd()
// ConcurrentDictionary<TKey, TValue>.TryUpdate()
// ConcurrentDictionary<TKey, TValue>.TryRemove()
let mutable numFailures = 0 // for bookkeeping
// Construct an empty dictionary
let cd = ConcurrentDictionary<int, string>()
// This should work
if cd.TryAdd(1, "one") |> not then
printfn "CD.TryAdd() failed when it should have succeeded"
numFailures <- numFailures + 1
// This shouldn't work -- key 1 is already in use
if cd.TryAdd(1, "uno") then
printfn "CD.TryAdd() succeeded when it should have failed"
numFailures <- numFailures + 1
// Now change the value for key 1 from "one" to "uno" -- should work
if cd.TryUpdate(1, "uno", "one") |> not then
printfn "CD.TryUpdate() failed when it should have succeeded"
numFailures <- numFailures + 1
// 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
printfn "CD.TryUpdate() succeeded when it should have failed"
numFailures <- numFailures + 1
// Remove key/value for key 1. Should work.
let mutable value1 = ""
if cd.TryRemove(1, &value1) |> not then
printfn "CD.TryRemove() failed when it should have succeeded"
numFailures <- numFailures + 1
// Remove key/value for key 1. Shouldn't work, because I already removed it
let mutable value2 = ""
if cd.TryRemove(1, &value2) then
printfn "CD.TryRemove() succeeded when it should have failed"
numFailures <- numFailures + 1
// If nothing went wrong, say so
if numFailures = 0 then
printfn " 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
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
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