Truncate expression preview result in builder widget if too long

Prevents window from resizing to extreme widths (fix #12433)

Author: nyalldawson

src/gui/qgsexpressionbuilderwidget.cpp

@@ -468,7 +468,7 @@ void QgsExpressionBuilderWidget::on_txtExpressionString_textChanged()
     {
       QVariant value = exp.evaluate( &mFeature, mLayer->pendingFields() );
       if ( !exp.hasEvalError() )
-        lblPreview->setText( value.toString() );
+        lblPreview->setText( formatPreviewString( value.toString() ) );
     }
     else
     {
@@ -483,7 +483,7 @@ void QgsExpressionBuilderWidget::on_txtExpressionString_textChanged()
     QVariant value = exp.evaluate();
     if ( !exp.hasEvalError() )
     {
-      lblPreview->setText( value.toString() );
+      lblPreview->setText( formatPreviewString( value.toString() ) );
     }
   }
 
@@ -509,6 +509,18 @@ void QgsExpressionBuilderWidget::on_txtExpressionString_textChanged()
   }
 }
 
+QString QgsExpressionBuilderWidget::formatPreviewString( const QString& previewString ) const
+{
+  if ( previewString.length() > 60 )
+  {
+    return QString( tr( "%1..." ) ).arg( previewString.left( 60 ) );
+  }
+  else
+  {
+    return previewString;
+  }
+}
+
 void QgsExpressionBuilderWidget::on_txtSearchEdit_textChanged()
 {
   mProxyModel->setFilterWildcard( txtSearchEdit->text() );

src/gui/qgsexpressionbuilderwidget.h

@@ -203,6 +203,12 @@ class GUI_EXPORT QgsExpressionBuilderWidget : public QWidget, private Ui::QgsExp
     void fillFieldValues( int fieldIndex, int countLimit );
     QString loadFunctionHelp( QgsExpressionItem* functionName );
 
+    /** Formats an expression preview result for display in the widget
+     * by truncating the string
+     * @param previewString expression preview result to format
+     */
+    QString formatPreviewString( const QString &previewString ) const;
+
     QString mFunctionsPath;
     QgsVectorLayer *mLayer;
     QStandardItemModel *mModel;
@@ -212,6 +218,7 @@ class GUI_EXPORT QgsExpressionBuilderWidget : public QWidget, private Ui::QgsExp
     QgsExpressionHighlighter* highlighter;
     bool mExpressionValid;
     QgsDistanceArea mDa;
+
 };
 
 #endif // QGSEXPRESSIONBUILDER_H