Bug report #6616
Preview in expression builder not always showing
|Affected QGIS version:||3.0.0||Regression?:||No|
|Operating System:||Easy fix?:||No|
|Pull Request or Patch supplied:||No||Resolution:|
|Crashes QGIS or corrupts data:||No||Copied to github as #:||15803|
The preview in the field calculator expression builder is often missing. This happens because the expression text is evaluated against the first feature in the layer. If the expression doesn't evaluate for the first feature there will be no text.
Thanks Nathan for the explanation.