# OpcClassicApplicationDescriptionCollection Members

> Reference: Represents a collection of OpcClassicApplicationDescription instances keyed by their ClassId.

<dl class="api-definition">
<dt>Type</dt>
<dd><a href="./">OpcClassicApplicationDescriptionCollection</a></dd>
<dt>Namespace</dt>
<dd><a href="../namespaces/opc.uafx.classic">Opc.UaFx.Classic</a></dd>
<dt>Assembly</dt>
<dd>Opc.UaFx.Advanced.dll</dd>
<dt>Package</dt>
<dd>Opc.UaFx.Advanced v2.59.0</dd>
</dl>

Inherits members from [KeyedCollection&lt;Guid, OpcClassicApplicationDescription&gt;](https://learn.microsoft.com/dotnet/api/system.collections.objectmodel.keyedcollection-2), [Collection&lt;OpcClassicApplicationDescription&gt;](https://learn.microsoft.com/dotnet/api/system.collections.objectmodel.collection-1).

## Constructors

### OpcClassicApplicationDescriptionCollection

Initializes a new instance of the [OpcClassicApplicationDescriptionCollection](https://www.traeger.de/en/docs/development/opcua/api/v2.59/opc.uafx.classic.opcclassicapplicationdescriptioncollection/) class.

<div class="api-signature" data-lang="csharp">

```csharp
public OpcClassicApplicationDescriptionCollection()
```

</div>

<div class="api-signature" data-lang="vbnet">

```vbnet
Public Sub New()
```

</div>

## Methods

### GetKeyForItem

<span class="api-meta">protected · override</span>

Extracts the key from the `item` specified.

<div class="api-signature" data-lang="csharp">

```csharp
protected override Guid GetKeyForItem(OpcClassicApplicationDescription item)
```

</div>

<div class="api-signature" data-lang="vbnet">

```vbnet
Protected Overrides Function GetKeyForItem(
    item As OpcClassicApplicationDescription) As Guid
```

</div>

**Parameters**

| Name | Type | Description |
|---|---|---|
| `item` | [OpcClassicApplicationDescription](https://www.traeger.de/en/docs/development/opcua/api/v2.59/opc.uafx.classic.opcclassicapplicationdescription/) | The [OpcClassicApplicationDescription](https://www.traeger.de/en/docs/development/opcua/api/v2.59/opc.uafx.classic.opcclassicapplicationdescription/) whose key is to be extracted. |

**Returns**

[Guid](https://learn.microsoft.com/dotnet/api/system.guid)

The [ClassId](https://www.traeger.de/en/docs/development/opcua/api/v2.59/opc.uafx.classic.opcclassicapplicationdescription/members#classid) of the `item`.

**Exceptions**

| Exception | Condition |
|---|---|
| [ArgumentNullException](https://learn.microsoft.com/dotnet/api/system.argumentnullexception) | The `item` is a null reference (Nothing in Visual Basic). |

**Overrides**

[GetKeyForItem(OpcClassicApplicationDescription)](https://learn.microsoft.com/dotnet/api/system.collections.objectmodel.keyedcollection-2.getkeyforitem)