Main.qml

//Main.qml
import QtQuick 2.7
import QtQuick.Controls 2.0
import QtQuick.Layouts 1.0
import customtype 1.0

ApplicationWindow {
    id: window
    visible: true
    width: 640
    height: 480
    title: qsTr("Application")

    CSharp {
        id: csharp
        Component.onCompleted: function() {
            console.log(csharp.TestMethod) // undefined
            csharp.TestMethod() // TypeError: Property 'TestMethod' of object CSharp(0xb7cb00) is not a function
        }
    }
}