public class TestObject
{
    public string StringProperty { get; set; }
    public int IntProperty { get; set; }
}

public class TestObjectsStorage
{
    public TestObject[] Data { get; }

    public TestObjectsStorage()
    {
        Data = new TestObject[10];

        for (var i = 0; i < Data.Length; ++i)
        {
            ar testObject = new TestObject
            {
                StringProperty = "Field N" + i,
                IntProperty = i
            };

            Data[i] = testObject;
        }
    }
}

app.UseDesigner(config =>
{
	config.SetLocateDataSource(() => new TestObjectsStorage());
});