Add method to access label string as expression, QgsExpression only created once then cached.

Author: NathanW2

src/CMakeLists.txt

@@ -4,10 +4,10 @@ ADD_SUBDIRECTORY(ui)
 ADD_SUBDIRECTORY(gui)
 ADD_SUBDIRECTORY(app)
 ADD_SUBDIRECTORY(providers)
-ADD_SUBDIRECTORY(plugins)
-ADD_SUBDIRECTORY(helpviewer)
+#ADD_SUBDIRECTORY(plugins)
+#ADD_SUBDIRECTORY(helpviewer)
 ADD_SUBDIRECTORY(crssync)
-ADD_SUBDIRECTORY(browser)
+#ADD_SUBDIRECTORY(browser)
 
 IF (WITH_BINDINGS)
   ADD_SUBDIRECTORY(python)

src/core/qgspallabeling.cpp

@@ -133,7 +133,7 @@ class QgsPalGeometry : public PalGeometry
 // -------------
 
 QgsPalLayerSettings::QgsPalLayerSettings()
-    : palLayer( NULL ), fontMetrics( NULL ), ct( NULL ), extentGeom( NULL )
+    : palLayer( NULL ), fontMetrics( NULL ), ct( NULL ), extentGeom( NULL ), expression( NULL )
 {
   placement = AroundPoint;
   placementFlags = 0;
@@ -195,6 +195,7 @@ QgsPalLayerSettings::QgsPalLayerSettings( const QgsPalLayerSettings& s )
   fontMetrics = NULL;
   ct = NULL;
   extentGeom = NULL;
+  expression = NULL;
 }
 
 
@@ -204,10 +205,19 @@ QgsPalLayerSettings::~QgsPalLayerSettings()
 
   delete fontMetrics;
   delete ct;
-
+  delete expression;
   delete extentGeom;
 }
 
+QgsExpression* QgsPalLayerSettings::getLabelExpression()
+{
+    if (expression == NULL)
+    {
+        expression = new QgsExpression( fieldName );
+    }
+    return expression;
+}
+
 static QColor _readColor( QgsVectorLayer* layer, QString property )
 {
   int r = layer->customProperty( property + "R" ).toInt();
@@ -458,17 +468,17 @@ void QgsPalLayerSettings::registerFeature(QgsVectorLayer* layer,  QgsFeature& f,
   // Check to see if we are a expression string.
   if (isExpression)
   {
-    QgsExpression exp( fieldName );
-    if ( exp.hasParserError() )
+    QgsExpression* exp = getLabelExpression();
+    if ( exp->hasParserError() )
     {
-      QgsDebugMsg("PASER HAS ERROR:" + exp.parserErrorString());
+      QgsDebugMsg("PASER HAS ERROR:" + exp->parserErrorString());
       return;
     }
-    QVariant result = exp.evaluate(&f,layer->dataProvider()->fields());
+    QVariant result = exp->evaluate(&f,layer->dataProvider()->fields());
     QgsDebugMsg("VALUE = " + result.toString());
-    if (exp.hasEvalError())
+    if (exp->hasEvalError())
     {
-       QgsDebugMsg("Expression Label Error = " + exp.evalErrorString());
+       QgsDebugMsg("Expression Label Error = " + exp->evalErrorString());
        return;
     }
     labelText  = result.toString();

src/core/qgspallabeling.h

@@ -46,9 +46,10 @@ namespace pal
 
 class QgsMapToPixel;
 class QgsFeature;
-#include "qgspoint.h"
 
+#include "qgspoint.h"
 #include "qgsmaprenderer.h" // definition of QgsLabelingEngineInterface
+#include "qgsexpression.h"
 
 class QgsPalGeometry;
 class QgsVectorLayer;
@@ -98,7 +99,15 @@ class CORE_EXPORT QgsPalLayerSettings
     };
 
     QString fieldName;
-    bool isExpression; // is this label made from a expression string eg FieldName || 'mm'
+
+    /** Is this label made from a expression string eg FieldName || 'mm'
+      */
+    bool isExpression;
+
+    /** Returns the QgsExpression for this label settings.
+      */
+    QgsExpression* getLabelExpression();
+
     Placement placement;
     unsigned int placementFlags;
     QFont textFont;
@@ -162,6 +171,7 @@ class CORE_EXPORT QgsPalLayerSettings
     /**Checks if a feature is larger than a minimum size (in mm)
     @return true if above size, false if below*/
     bool checkMinimumSizeMM( const QgsRenderContext& ct, QgsGeometry* geom, double minSize ) const;
+    QgsExpression* expression;
 };
 
 class CORE_EXPORT QgsLabelCandidate

src/gui/qgsexpressionbuilder.h

@@ -55,13 +55,21 @@ class QgsExpressionItem : public QStandardItem
 
         QString getExpressionText() {   return mExpressionText;  }
 
+        /** Get the help text that is associated with this expression item.
+          *
+          * @return The help text.
+          */
         QString getHelpText() {  return mHelpText;  }
         /** Set the help text for the current item
           *
           * @note The help text can be set as a html string.
           */
         void setHelpText(QString helpText) { mHelpText = helpText; }
 
+        /** Get the type of expression item eg header, field, ExpressionNode.
+          *
+          * @return The QgsExpressionItem::ItemType
+          */
         QgsExpressionItem::ItemType getItemType() { return mType ; }
 
     private: