Dictionary TryGetValue Example
This page was last reviewed on Oct 26, 2023.
Dot Net Perls
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.
If Then
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 Module
50 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.
Dictionary GetValueOrDefault
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 Module
0 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.
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Sam Allen is passionate about computer languages. In the past, his work has been recommended by Apple and Microsoft and he has studied computers at a selective university in the United States.
This page was last updated on Oct 26, 2023 (new).
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