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Expression preview widget: do not disable feature picker (fixes #38646) #38797

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merged 1 commit into from
Sep 16, 2020
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Expression preview widget: do not disable feature picker (fixes #38646) #38797

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25 changes: 11 additions & 14 deletions src/gui/qgsexpressionpreviewwidget.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -49,20 +49,7 @@ void QgsExpressionPreviewWidget::setCurrentFeature( const QgsFeature &feature )
{
// todo: update the combo box if it has been set externaly?

// force the feature to be valid, so it can evaluate an invalid feature but having its fields set
if ( !feature.isValid() )
{
QgsFeature validFeature( feature );
validFeature.setValid( true );
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if you remove this, that will bring back the issue when a layer is empty and you try an expression (#37100).
Or am I missing something?

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With this pull request, if the layer is empty (or you specify an invalid FID),

  • if the expression doesn't use fields, then it is evaluated
  • if the expression uses fields, the preview label displays "No feature was found on this layer to evaluate the expression" (not that the expression is invalid)

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ok, that makes sense.

mExpressionContext.setFeature( validFeature );
mFeaturePickerWidget->setEnabled( false );
mFeaturePickerWidget->setToolTip( tr( "No feature was found on this layer to evaluate the expression." ) );
}
else
{
mExpressionContext.setFeature( feature );
mFeaturePickerWidget->setEnabled( true );
}
mExpressionContext.setFeature( feature );
refreshPreview();
}

Expand Down Expand Up @@ -93,6 +80,16 @@ void QgsExpressionPreviewWidget::refreshPreview()
{
mExpression = QgsExpression( mExpressionText );

if ( !mExpressionContext.feature().isValid() )
{
if ( !mExpression.referencedColumns().isEmpty() || mExpression.needsGeometry() )
{
mPreviewLabel->setText( tr( "No feature was found on this layer to evaluate the expression." ) );
mPreviewLabel->setStyleSheet( QStringLiteral( "color: rgba(255, 6, 10, 255);" ) );
return;
}
}

if ( mUseGeomCalculator )
{
// only set an explicit geometry calculator if a call to setGeomCalculator was made. If not,
Expand Down