c# Reflection change get method of a property

Question

In my C# project I have a dependency on a 3rd party library. Now I want to write an automated acceptance test for my project. However to invoke the test I need an instance of a class from the 3rd party library. Using reflection I managed to set the values as I needed them apart from one.

Here is the relevant class that I am having the issue with:

public class SystemResults
{
    // There must be something like this. However I cannot see it as it is private.
    private List<Positions> xyz = new List<Positions>();

    public IList<Positions> Positions
    {
        get
        {
            return xyz;
        }

        // This property does not have a set method
    }
}

Here is what I have tried so far:

private void InitSystemResults(Type trueSysResType, SystemResults sysRes)
{
    List<Position> positions = ImporterTools.GetPositions(PositionsCsv);
    trueSysResType.GetProperty("Positions").SetValue(sysRes, positions); // ==> Here I get an exception
}

When I invoke the SetValue() method the following exception is thrown.

System.ArgumentException : Property set method not found.

From this information I figured out, that the class must look as I described above.

Now I would like to proceed with this some how. Has anybody an idea how I can achieve that when I access sysRes.Positions my positions are returned by the get method? Or is there a way to change the get method?

read this up.might help https://stackoverflow.com/questions/135020/advantages-to-using-private-static-methods — Jephren Naicker, Sep 06 '17 at 05:19

score 2 · Accepted Answer · answered Sep 06 '17 at 05:24

You can use BindingFlags.NonPublic,

FieldInfo[] fields = typeof(SystemResults).GetFields(
                         BindingFlags.NonPublic |
                         BindingFlags.Instance).ToArray(); // gets xyz and the other private fields

List<int> testResults = new List<int>() { 1,23,4,5,6,7}; // list of integer to set

SystemResults sysres = new SystemResults(); // instance of object
fields[0].SetValue(sysres, testResults); // I know that fields[0] is xyz (you need to find it first), 
// sets list of int to object

Hope helps,

you are a hero! ;) That worked just fine. Many thanks! – Konstantin Sep 06 '17 at 05:33 — Konstantin, Sep 06 '17 at 05:33

tymtam · Answer 2 · 2017-09-06T05:28:57.213

0

{get;} only properties can have a backing field but Positions may be returning something completely different (not a value of a backing field, but maybe a result of a function).

Your code could accept ISystemResults which you can mock and in real code you could have a class SystemResultsFacade which internally calls the 3rd party code.

edited Sep 06 '17 at 05:28

answered Sep 06 '17 at 05:14

tymtam

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That is true. Did not consider that. – Konstantin Sep 06 '17 at 05:16
@PeterDuniho Good point, thanks. I was talking nonsense - I was thinking about expression based properties. Answer updated. – tymtam Sep 06 '17 at 05:31

c# Reflection change get method of a property

2 Answers2