How to let custom property pane fields enable the apply button in SharePoint Framework
August 30, 2017
Since the SharePoint Framework v1.2.0 release; it is now possible to let your custom property pane fields trigger the apply button in non-reactive property panes. Before this release, you had to implement your own logic to re-render the contents of your web part or use the reactive property pane.
So, what changed?
In the previous versions, the onRender method of your custom property pane field had two arguments:
The HTML element
Since version 1.2.0 a new argument has been added:
Change callback function
This is a callback function which gets provided to your custom field by the property pane. You can make use of this to let the property pane know a change happened in one of your custom fields. If you use this in combination with a non-reactive property pane (that is the property pane with an apply button at the bottom) it will trigger the button to get enabled.