Boolean Dictionary Dictionary GetValueOrDefault If

`TryGetValue`

In VB.NET programs there are many ways to access values based on keys in a Dictionary. But TryGetValue is one of the safest and most effective.

With this function, we receive a value only if the key exists. It returns a Boolean telling us whether the key exists. TryGetValue is often used in an If.

Example

For showing the usage of TryGetValue, we must first have a Dictionary. The program creates a Dictionary and populates it as we begin.

Part 1 We use TryGetValue on a key that exists in the colors Dictionary. The "test" variable is assigned to 50.

Part 2 We can use TryGetValue without an If. The result variable will be left with its initial value if no key is found.

Part 3 If the key is not found, TryGetValue returns False. In some programs, knowing a key is missing is helpful.

Module Module1
    Sub Main()
        Dim colors = New Dictionary(Of String, Integer)
        colors.Add("red", 50)
        colors.Add("orange", 51)

        ' Part 1: use TryGetValue to get an existing value.
        Dim test = 0
        If colors.TryGetValue("red", test)
            Console.WriteLine(test)
        End If

        ' Part 2: use TryGetValue without If.
        Dim test2 = 0
        colors.TryGetValue("orange", test2)
        Console.WriteLine(test2)

        ' Part 3: use TryGetValue when no key exists.
        Dim test3 = 0
        If colors.TryGetValue("cat", test3)
            ' Not reached.
        Else
            Console.WriteLine("Cat not found!")
        End If
    End Sub
End Module50
51
Cat not found!

`GetValueOrDefault`

Another function that can perform a similar task to TryGetValue is GetValueOrDefault. In a sense, GetValueOrDefault is like TryGetValue without an If-statement.

Part 1 We use TryGetValue on a key that does not exist in the Dictionary, and the result is left with its initial value 0.

Part 2 We use GetValueOrDefault, and the default value for Integer is returned, which is also the value 0.

Module Module1
    Sub Main()
        Dim sizes = New Dictionary(Of Char, Integer)
        sizes.Add("s", 1)
        sizes.Add("m", 2)
        sizes.Add("l", 3)

        ' Part 1: use TryGetValue.
        Dim result1 = 0
        sizes.TryGetValue("z", result1)
        Console.WriteLine(result1)

        ' Part 2: use GetValueOrDefault.
        Dim result2 = sizes.GetValueOrDefault("z")
        Console.WriteLine(result2)
    End Sub
End Module0
0

Summary

Accessing keys to look up values in a Dictionary is frequently done in VB.NET programs. With TryGetValue and its companion function GetValueOrDefault, this is done safely.