This property provides the ability to access a specific element in the collection by using the following syntax: myCollection[key].
You can also use the Item property to add new elements by setting the value of a key that does not exist in the dictionary (for example, myCollection["myNonexistentKey"] = myValue). However, if the specified key already exists in the dictionary, setting the Item property overwrites the old value. In contrast, the Add method does not modify existing elements.
Implementations can vary in whether they allow the key to be nullNothingnullptra null reference (Nothing in Visual Basic).
The C# language uses the this keyword to define the indexers instead of implementing the Item property. Visual Basic implements Item as a default property, which provides the same indexing functionality.