Improve preview of current variable value in expression builder

Author: nyalldawson

python/core/qgsexpression.sip

@@ -692,6 +692,14 @@ class QgsExpression
      */
     static QString group( const QString& group );
 
+    /** Formats an expression result for friendly display to the user. Truncates the result to a sensible
+     * length, and presents text representations of non numeric/text types (eg geometries and features).
+     * @param value expression result to format
+     * @returns formatted string, may contain HTML formatting characters
+     * @note added in QGIS 2.14
+     */
+    static QString formatPreviewString( const QVariant& value );
+
   protected:
     void initGeomCalculator();
 };

src/core/qgsexpression.cpp

@@ -4561,13 +4561,9 @@ QString QgsExpression::variableHelpText( const QString &variableName, bool showV
     {
       valueString = QCoreApplication::translate( "variable_help", "not set" );
     }
-    else if ( value.type() == QVariant::String )
-    {
-      valueString = QString( "'<b>%1</b>'" ).arg( value.toString() );
-    }
     else
     {
-      valueString = QString( "<b>%1</b>" ).arg( value.toString() );
+      valueString = QString( "<b>%1</b>" ).arg( formatPreviewString( value ) );
     }
     text.append( QCoreApplication::translate( "variable_help", "<p>Current value: %1</p>" ).arg( valueString ) );
   }
@@ -4602,6 +4598,47 @@ QString QgsExpression::group( const QString& name )
   return gGroups.value( name, name );
 }
 
+QString QgsExpression::formatPreviewString( const QVariant& value )
+{
+  if ( value.canConvert<QgsGeometry>() )
+  {
+    //result is a geometry
+    QgsGeometry geom = value.value<QgsGeometry>();
+    if ( geom.isEmpty() )
+      return tr( "<i>&lt;empty geometry&gt;</i>" );
+    else
+      return tr( "<i>&lt;geometry: %1&gt;</i>" ).arg( QgsWKBTypes::displayString( geom.geometry()->wkbType() ) );
+  }
+  else if ( value.canConvert< QgsFeature >() )
+  {
+    //result is a feature
+    QgsFeature feat = value.value<QgsFeature>();
+    return tr( "<i>&lt;feature: %1&gt;</i>" ).arg( feat.id() );
+  }
+  else if ( value.canConvert< QgsExpression::Interval >() )
+  {
+    //result is a feature
+    QgsExpression::Interval interval = value.value<QgsExpression::Interval>();
+    return tr( "<i>&lt;interval: %1 days&gt;</i>" ).arg( interval.days() );
+  }
+  else if ( value.type() == QVariant::String )
+  {
+    QString previewString = value.toString();
+    if ( previewString.length() > 63 )
+    {
+      return QString( tr( "'%1...'" ) ).arg( previewString.left( 60 ) );
+    }
+    else
+    {
+      return previewString.prepend( '\'' ).append( '\'' );
+    }
+  }
+  else
+  {
+    return value.toString();
+  }
+}
+
 QVariant QgsExpression::Function::func( const QVariantList& values, const QgsFeature* feature, QgsExpression* parent )
 {
   //default implementation creates a QgsFeatureBasedExpressionContext

src/core/qgsexpression.h

@@ -1052,6 +1052,14 @@ class CORE_EXPORT QgsExpression
      */
     static QString group( const QString& group );
 
+    /** Formats an expression result for friendly display to the user. Truncates the result to a sensible
+     * length, and presents text representations of non numeric/text types (eg geometries and features).
+     * @param value expression result to format
+     * @returns formatted string, may contain HTML formatting characters
+     * @note added in QGIS 2.14
+     */
+    static QString formatPreviewString( const QVariant& value );
+
   protected:
     /**
      * Used by QgsOgcUtils to create an empty

src/gui/qgsexpressionbuilderwidget.cpp

@@ -557,7 +557,7 @@ void QgsExpressionBuilderWidget::on_txtExpressionString_textChanged()
       mExpressionContext.setFeature( mFeature );
       QVariant value = exp.evaluate( &mExpressionContext );
       if ( !exp.hasEvalError() )
-        lblPreview->setText( formatPreviewString( value ) );
+        lblPreview->setText( QgsExpression::formatPreviewString( value ) );
     }
     else
     {
@@ -572,7 +572,7 @@ void QgsExpressionBuilderWidget::on_txtExpressionString_textChanged()
     QVariant value = exp.evaluate( &mExpressionContext );
     if ( !exp.hasEvalError() )
     {
-      lblPreview->setText( formatPreviewString( value ) );
+      lblPreview->setText( QgsExpression::formatPreviewString( value ) );
     }
   }
 
@@ -598,44 +598,6 @@ void QgsExpressionBuilderWidget::on_txtExpressionString_textChanged()
   }
 }
 
-QString QgsExpressionBuilderWidget::formatPreviewString( const QVariant& value ) const
-{
-  if ( value.canConvert<QgsGeometry>() )
-  {
-    //result is a geometry
-    QgsGeometry geom = value.value<QgsGeometry>();
-    if ( geom.isEmpty() )
-      return tr( "<i>&lt;empty geometry&gt;</i>" );
-    else
-      return tr( "<i>&lt;geometry: %1&gt;</i>" ).arg( QgsWKBTypes::displayString( geom.geometry()->wkbType() ) );
-  }
-  else if ( value.canConvert< QgsFeature >() )
-  {
-    //result is a feature
-    QgsFeature feat = value.value<QgsFeature>();
-    return tr( "<i>&lt;feature: %1&gt;</i>" ).arg( feat.id() );
-  }
-  else if ( value.canConvert< QgsExpression::Interval >() )
-  {
-    //result is a feature
-    QgsExpression::Interval interval = value.value<QgsExpression::Interval>();
-    return tr( "<i>&lt;interval: %1 days&gt;</i>" ).arg( interval.days() );
-  }
-  else
-  {
-    QString previewString = value.toString();
-
-    if ( previewString.length() > 63 )
-    {
-      return QString( tr( "%1..." ) ).arg( previewString.left( 60 ) );
-    }
-    else
-    {
-      return previewString;
-    }
-  }
-}
-
 void QgsExpressionBuilderWidget::loadExpressionContext()
 {
   QStringList variableNames = mExpressionContext.filteredVariableNames();

src/gui/qgsexpressionbuilderwidget.h

@@ -261,12 +261,6 @@ class GUI_EXPORT QgsExpressionBuilderWidget : public QWidget, private Ui::QgsExp
     QString loadFunctionHelp( QgsExpressionItem* functionName );
     QString helpStylesheet() const;
 
-    /** Formats an expression preview result for display in the widget
-     * by truncating the string
-     * @param value expression preview result to format
-     */
-    QString formatPreviewString( const QVariant& value ) const;
-
     void loadExpressionContext();
 
     bool mAutoSave;