CODEWITHSUNDEEP
c#genericsreflection
Dominic Cotton
Dominic Cotton

Reputation: 819

Method.Invoke failing with Parameter Count Mismatch

I am trying to invoke a generic method. The definition of the method is as follows:

public System.Collections.Generic.IList<T> Query<T>(string query, [string altUrl = ""])
where T : new()

This is from the SalesforceSharp library on github. I am trying to make an additional service layer over this call and am struggling to invoke it. See my code below.

public List<T> Query<T>()
    {
        //IList<Salesforce.Account> _returnList = null;
        IList<T> _returnList = null;
        Type _t = typeof(T);

        SqlBuilder _sb = new SqlBuilder();
        _sb.Table = _t.Name.ToString();
        foreach (PropertyInfo p in _t.GetProperties()) _sb.Fields.Add(p.Name.ToString());

        MethodInfo method = _Client.GetType().GetMethod("Query");
        method = method.MakeGenericMethod(_t);
        try
        {
            object[] _prms = new object[1];
            _prms[0] = _sb.SQL;
            _returnList = (IList<T>)method.Invoke(_Client, new object[] { _prms });
            //_returnList = _Client.Query<Salesforce.Account>(_sb.SQL);
        }
        catch { }
        return (List<T>)_returnList;
    }

If I run this i get a Parameter Count Mismatch exception on the method.invoke line, but i am confused because if i bring in the two uncommented lines and execute without the generic call it is working ok. I have tried many combinations of string arrays wrapped in object arrays, strings in strings, etc but can't get it to go. I thought maybe it was treating the second parameter as mandatory? but adding another object to my _prms array didnt work either.

Please help!

Thanks, Dom

Upvotes: 5

Views: 3836

Answers (2)

Yacoub Massad
Yacoub Massad

Reputation: 27861

For optional parameters that you don't want to specify a value for, you have to pass Type.Missing like this:

_returnList = (IList<T>)method.Invoke(_Client, new object[] { _sb.SQL, Type.Missing });

Quoting from this reference:

Use the Missing field for invocation through reflection to obtain the default value of a parameter

Please note also that another problem is that you are currently passing an object[] instead of just the query string.

Upvotes: 9

Selman Gen&#231;
Selman Gen&#231;

Reputation: 101681

The optional parameters are just syntactic sugars, when you don't supply an optional parameter compiler calls the method with the given default value. But in case of Reflection, you need to do it manually.

object[] _prms = new object[2];
_prms[0] = _sb.SQL;
_prms[1] = "";
 _returnList = (IList<T>)method.Invoke(_Client, _prms);

Upvotes: 0

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