Changing the number of steps on the animation widget causes napari to crash if no frame has yet been captured

[ptbrown1729]

Changing the number of steps on the animation widget causes napari to crash if no frame has yet been captured.

Minimal example: run the following code

import numpy as np
import napari
from napari_animation import AnimationWidget

viewer = napari.Viewer()

animation_widget = AnimationWidget(viewer)
viewer.window.add_dock_widget(animation_widget, area='right')
viewer.add_image(np.random.rand(301, 301, 301))

After napari launches, click the "+" button on the animation widget. This gives the following error

WARNING: Traceback (most recent call last):
  File "c:\users\ptbrown2\documents\napari-animation\napari_animation\_qt\frame_widget.py", line 56, in _update_animation_steps
    active_keyframe.steps = self.stepsSpinBox.value()
AttributeError: 'NoneType' object has no attribute 'steps'
Process finished with exit code -1073740791 (0xC0000409)

napari: 0.4.10 Platform: Windows-10-10.0.17763-SP0 Python: 3.8.5 (default, Sep 3 2020, 21:29:08) [MSC v.1916 64 bit (AMD64)] Qt: 5.9.7 PyQt5: 5.9.2 NumPy: 1.19.2 SciPy: 1.6.2 Dask: 2021.04.0 VisPy: 0.6.6

OpenGL:

• GL version: 4.6.0 NVIDIA 442.19
• MAX_TEXTURE_SIZE: 16384

Screens:

• screen 1: resolution 1920x1080, scale 1.0

Plugins:

• animation: 0.0.3.dev69+gaab5909
• console: 0.0.3
• scikit-image: 0.4.7
• svg: 0.1.4

[alisterburt]

Hi @ptbrown1729 thanks for the clear report!

Looks like a workaround for this would be to add

if active_keyframe is None:
    return

in the callback here between L55 and L56

https://github.com/napari/napari-animation/blob/aab59095ca0d4022014ff48b2c2a9620da20cdac/napari_animation/_qt/frame_widget.py#L53-L59

If you wanted to make this change yourself PRs are always welcome! Otherwise, thanks for taking the time to report and I'll make the change myself soon 🙂

[ptbrown1729]

Sure, I'm happy to submit a PR