Data defined must reprepare expression if expression changes

Author: nyalldawson

src/core/qgsdatadefined.cpp

@@ -39,6 +39,12 @@ QgsDataDefined::~QgsDataDefined()
   delete mExpression;
 }
 
+void QgsDataDefined::setExpressionString( const QString &expr )
+{
+  mExpressionString = expr;
+  mExpressionPrepared = false;
+}
+
 bool QgsDataDefined::prepareExpression( QgsVectorLayer* layer )
 {
   if ( !mUseExpression || mExpressionString.isEmpty() )

src/core/qgsdatadefined.h

@@ -54,7 +54,7 @@ class CORE_EXPORT QgsDataDefined
     void setUseExpression( bool use ) { mUseExpression = use; }
 
     QString expressionString() const { return mExpressionString; }
-    void setExpressionString( const QString& expr ) { mExpressionString = expr; }
+    void setExpressionString( const QString& expr );
 
     // @note not available in python bindings
     QMap<QString, QVariant> expressionParams() const { return mExpressionParams; }