Your gevallenList is also adding the listviewitem without a text property. It doesn't matter whether you set the text property previously before adding it. Where you are adding it, you are not adding the text property to the item when it's being added to the control, but instead, you are adding the whole object instead. This is normal to see {SomeValue} in curly brackets when you add an object of this type, because you are not calling on the text property upon adding it. There was no need to change any of your code.
Next time you post a topic, please remember to post your code in code tags, and it would also be helpful if you spend the time telling us what the names of what your controls are.