--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/gwt-client/src/main/java/org/dive4elements/river/client/client/ui/WaterlevelTwinPanelValidator.java	Thu Jan 18 18:32:30 2018 +0100
@@ -0,0 +1,48 @@
+/** Copyright (C) 2017 by Bundesanstalt für Gewässerkunde
+ * Software engineering by 
+ *  Björnsen Beratende Ingenieure GmbH 
+ *  Dr. Schumacher Ingenieurbüro für Wasser und Umwelt
+ *
+ * This file is Free Software under the GNU AGPL (>=v3)
+ * and comes with ABSOLUTELY NO WARRANTY! Check out the
+ * documentation coming with Dive4Elements River for details.
+ */
+package org.dive4elements.river.client.client.ui;
+
+import java.util.ArrayList;
+import java.util.List;
+
+import org.dive4elements.river.client.client.FLYSConstants;
+import org.dive4elements.river.client.client.ui.AbstractPairRecommendationPanel.IValidator;
+
+import com.smartgwt.client.widgets.grid.ListGrid;
+import com.smartgwt.client.widgets.grid.ListGridRecord;
+
+/**
+ * Contains the old code from the validate-method of the DatacageTwinPanel.
+ *  
+ * @author Gernot Belger
+ */
+public final class WaterlevelTwinPanelValidator implements IValidator {
+
+	@Override
+	public List<String> validate(final ListGrid differencesList, final FLYSConstants msgProvider) {
+		
+        final List<String> errors = new ArrayList<String>();
+        if (differencesList.getRecords().length == 0) {
+        	// FIXME: waterlevel dependent! This will lead to a bad error message in English, for M-Info/Bed-Differences calculation
+            errors.add(msgProvider.error_no_waterlevel_pair_selected());
+        }
+        // Check whether minuend and subtrahend are equal.
+        for (ListGridRecord record: differencesList.getRecords()) {
+            RecommendationPairRecord r = (RecommendationPairRecord) record;
+            if (r.getFirst().equals(r.getSecond())) {
+            	// FIXME: this is still waterlevel specific!
+            	// TODO: delegate validation to specific implementations
+                errors.add(msgProvider.error_same_waterlevels_in_pair());
+            }
+        }
+
+        return errors;
+	}
+}
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