Proper way to initialize a C# dictionary with values

With C# 6.0, you can create a dictionary in the following way:

var dict = new Dictionary<string, int> { ["one"] = 1, ["two"] = 2, ["three"] = 3 }; 

It even works with custom types.

Suppose we have a dictionary like this:

Dictionary<int, string> dict = new Dictionary<int, string>(); dict.Add(1, "Mohan"); dict.Add(2, "Kishor"); dict.Add(3, "Pankaj"); dict.Add(4, "Jeetu"); 

We can initialize it as follows.

Dictionary<int, string> dict = new Dictionary<int, string> { { 1, "Mohan" }, { 2, "Kishor" }, { 3, "Pankaj" }, { 4, "Jeetu" } }; 

You can initialize a Dictionary (and other collections) inline. Each member is contained with braces:

Dictionary<int, StudentName> students = new Dictionary<int, StudentName> { { 111, new StudentName { FirstName = "Sachin", LastName = "Karnik", ID = 211 } }, { 112, new StudentName { FirstName = "Dina", LastName = "Salimzianova", ID = 317 } }, { 113, new StudentName { FirstName = "Andy", LastName = "Ruth", ID = 198 } } }; 

See How to initialize a dictionary with a collection initializer (C# Programming Guide) for details.

Note that C# 9 allows Target-typed new expressions so if your variable or a class member is not abstract class or interface type duplication can be avoided:

 private readonly Dictionary<string, XlFileFormat> FILE_TYPE_DICT = new () { { "csv", XlFileFormat.xlCSV }, { "html", XlFileFormat.xlHtml } }; 

Object initializers were introduced in C# 3.0. Check which framework version you are targeting.

Overview of C# 3.0

With С# 6.0

var myDict = new Dictionary<string, string> { ["Key1"] = "Value1", ["Key2"] = "Value2" }; 

Here is an example of Dictionary with Dictionary value

Dictionary<string, Dictionary<int, string>> result = new() { ["success"] = new() { { 1, "ok" }, { 2, "ok" } }, ["fail"] = new() { { 3, "some error" }, { 4, "some error 2" } }, }; 

which is equivalent to this in JSON :

{ "success": { "1": "ok", "2": "ok" }, "fail": { "3": "some error", "4": "some error 4" } }