Convert Dictionary(Of String, Object) to Dictionary(Of String, String)

Question

When I try to pass a Dictionary(Of String, Object) to a function parameter that wants a Dictionary(Of String, String) I get the following error:

Unable to cast object of type 'System.Collections.Generic.Dictionary'2[System.String,System.Object]' to type 'System.Collections.Generic.Dictionary'2[System.String,System.String]'.

All of the Object values in the dictionary are strings but the dictionary was declared as String/Object. I would have thought that the system would be able to convert this but since it isn't I need to do it myself.

I looked at the .ToDictionary() prototype method but all of the examples show a list being converted to a dictionary.

I found this question which has an accepted answer for what I want but it's written in C# and I can't figure out the conversion to VB.Net.

Edit 1

Offending code. Obviously boiled down or else I would just simply declare dict1 as string/string in my actual code.

Dim dict1 As New Dictionary(Of String, Object) From {{"key1","value1"}}

SomeFunctionThatExpectsParamToBeDictOfStringString(dict1)

Edit 2

I tried:

SomeFunctionThatExpectsParamToBeDictOfStringString(dict1.ToDictionary(Function(k) k.Key, Function(v) v.Value.ToString()))

but got:

System.MissingMemberException: Public member 'ToDictionary' on type 'Dictionary(Of String,Object)' not found.

If you really know every item is a string, the best solution here is to change the declaration of the dictionary. — Joel Coehoorn
– Joel Coehoorn, Commented Feb 25, 2020 at 21:52
Regardless of the fact that you know all of the Objects are really Strings, the type system doesn't know that (if it did, it would be a Dictionary(Of String, String) rather than a Dictionary(Of String, Object)). And while it might make sense to treat a dictionary from string to string as a dictionary from string to object, it really doesn't make sense to go in the other direction, because the dictionary can legally contain things that aren't strings. — Craig
– Craig, Commented Feb 26, 2020 at 14:27
The dictionary is generated inside of, and returned from a method. Sometimes this dictionary does need to be a string/object because the objects are a mix of strings, integers, and decimals. In other cases, it is a string/object where the objects are all strings. Regardless, I should be able to convert the dict of string/object to string/string since all of the potential objects can easily be converted to a string value. It just so happens that I only need to convert this dict of string/object when all the objects are strings but again, it shouldn't matter if that was not the case either. — Drew
– Drew, Commented Feb 26, 2020 at 14:42

Steve · Accepted Answer · 2020-02-26 10:06:19Z

5

This could be the VB.NET version of the C# code you have linked

Dim dic1 As Dictionary(Of String, Object) = New Dictionary(Of String, Object) 
dic1.Add("A", "B")

Dim dic2 As Dictionary(Of String, String) = dic1.ToDictionary(Function(k) k.Key, 
                                                              Function(v) v.Value.ToString())

edited Feb 26, 2020 at 10:06

answered Feb 25, 2020 at 21:30

Steve

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7 Comments

Drew Over a year ago

Please see Edit2

Steve Over a year ago

That's seems to be a missing Imports System.Linq

Drew Over a year ago

Same error. I don't think its related but the dictionary I am trying to convert is the result of a Union of two other dictionaries: dict1.Union(dict2).ToDictionary(Function(d) d.Key, Function(d) d.Value)

Mary Over a year ago

.ToDictionary doesn't change dic1. It produces a new dictionary. Trying to pass dic1 will not have desired result. Try assigning to a new variable of the proper type before passing to your function

Drew Over a year ago

@Steve, I agree this should be working. I am accepting your answer. As far as something happening dynamically, the dictionary is being built and returned from a function. When debugging, the returned dictionary looks like this: System.Collections.Generic.Dictionary`2[System.String,System.Object]]} System.Collections.Generic.KeyValuePair(Of String, Object)

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