# I want to creat a qMRMLNodeCombobox to choose one of fiducial node

**URL:** https://discourse.slicer.org/t/i-want-to-creat-a-qmrmlnodecombobox-to-choose-one-of-fiducial-node/44496
**Category:** Development
**Created:** [September 16, 2025, 12:49pm UTC](https://discourse.slicer.org/t/i-want-to-creat-a-qmrmlnodecombobox-to-choose-one-of-fiducial-node/44496 "2025-09-16T12:49:44Z")
**Posts on this page:** 5
**Page:** 1

<div class="post-metadata">

### Author: ![zhutouzjq](https://avatars.discourse-cdn.com/v4/letter/z/8797f3/32.png) [@zhutouzjq](https://discourse.slicer.org/u/zhutouzjq)
#### Post date: [September 16, 2025, 12:49pm UTC](https://discourse.slicer.org/t/i-want-to-creat-a-qmrmlnodecombobox-to-choose-one-of-fiducial-node/44496/1 "2025-09-16T12:49:45Z")

</div>

I know this question may be stupid, but it has been already struggling me for several days.

as you see, there is a fiducial node in the CTA image.

 ![无标题](https://us1.discourse-cdn.com/flex002/uploads/slicer/original/3X/6/4/642850957d4a297a1dcd8cd9e437f48f9cc2f819.png)

and I created a standard intial extension, insert a label called ‘lowerpoint’ and a qMRMLNodeCombobox.

 ![无标题-1](https://us1.discourse-cdn.com/flex002/uploads/slicer/original/3X/b/7/b7f3b7ea089ab0f062f010c8813078deb6c1e760.png)

I want to use this qMRMLNodeCombobox to choose the fiducial node, but the combobox is gray and can’t to interact with mouse. So, how can I use the combobox to choose the fiducial node?

---

<div class="post-metadata">

### Author: ![jamesobutler](https://sea2.discourse-cdn.com/flex002/user_avatar/discourse.slicer.org/jamesobutler/32/7511_2.png) [@jamesobutler](https://discourse.slicer.org/u/jamesobutler)
#### Post date: [September 16, 2025, 12:59pm UTC](https://discourse.slicer.org/t/i-want-to-creat-a-qmrmlnodecombobox-to-choose-one-of-fiducial-node/44496/2 "2025-09-16T12:59:15Z")

</div>

I suspect the qMRMLNodeComboBox doesn’t yet have the mrmlScene set for it. MRML widgets are grey like that when this is the case.

```auto
node_combobox.setMRMLScene(slicer.mrmlScene)

```

---

<div class="post-metadata">

### Author: ![zhutouzjq](https://avatars.discourse-cdn.com/v4/letter/z/8797f3/32.png) [@zhutouzjq](https://discourse.slicer.org/u/zhutouzjq)
#### Post date: [September 17, 2025, 12:54am UTC](https://discourse.slicer.org/t/i-want-to-creat-a-qmrmlnodecombobox-to-choose-one-of-fiducial-node/44496/3 "2025-09-17T00:54:43Z")

</div>

sincerely thank you for your anwser. Magic, with only one line of code, this problem is just sovled. Magic

---

<div class="post-metadata">

### Author: ![cpinter](https://sea2.discourse-cdn.com/flex002/user_avatar/discourse.slicer.org/cpinter/32/7995_2.png) [@cpinter](https://discourse.slicer.org/u/cpinter)
#### Post date: [September 17, 2025, 11:32am UTC](https://discourse.slicer.org/t/i-want-to-creat-a-qmrmlnodecombobox-to-choose-one-of-fiducial-node/44496/4 "2025-09-17T11:32:03Z")

</div>

If you created the UI with Qt designer, I think the step that you missed was making the connection between the parent widget’s `mrmlSceneChanged` signal and the combobox’ `setMRMLScene` function. You can do it by switching to Edit Signals/Slots mode (F4). Normally if we create a UI in designer, we do that instead of adding this line in the code (that way there is no question about when to call it exactly).

---

<div class="post-metadata">

### Author: ![zhutouzjq](https://avatars.discourse-cdn.com/v4/letter/z/8797f3/32.png) [@zhutouzjq](https://discourse.slicer.org/u/zhutouzjq)
#### Post date: [September 18, 2025, 1:26am UTC](https://discourse.slicer.org/t/i-want-to-creat-a-qmrmlnodecombobox-to-choose-one-of-fiducial-node/44496/5 "2025-09-18T01:26:27Z")

</div>

yes，these operation in Qt is same to add a line of code.

for example, to activate the qMRMLNodeCombobox in the extension.

 ![无标题](https://us1.discourse-cdn.com/flex002/uploads/slicer/original/3X/a/8/a8a9634ee8ef08def2a3669600f368c28641b503.png)

i first change the nodetype of the new qMRMLNodeCombobox

 ![无标题-3](https://us1.discourse-cdn.com/flex002/uploads/slicer/original/3X/8/c/8cbc7031f1affdffce94642eb5786bdff1a58cd6.png)

and then press F4 as you say

 ![无标题-1](https://us1.discourse-cdn.com/flex002/uploads/slicer/original/3X/d/f/dfd1c54386a30e8f250369a41a606d193aec77b9.png)

finally link the edge of widget to this qMRMLNodeCombobox, and choose this option.

 ![无标题-2](https://us1.discourse-cdn.com/flex002/uploads/slicer/original/3X/e/f/effbaf5f4b9cb92f048b46242b73a72dda139e05.png)

after reloading, the qMRMLNodeCombobox called upperpoint can also choose the fiducial points in markups.