--- a/flys-client/src/main/java/de/intevation/flys/client/client/ui/AbstractUIProvider.java	Thu Jun 09 10:57:42 2011 +0000
+++ b/flys-client/src/main/java/de/intevation/flys/client/client/ui/AbstractUIProvider.java	Thu Jun 09 14:06:10 2011 +0000
@@ -5,6 +5,7 @@
 
 import com.google.gwt.core.client.GWT;
 
+import com.smartgwt.client.util.SC;
 import com.smartgwt.client.widgets.Canvas;
 import com.smartgwt.client.widgets.Img;
 import com.smartgwt.client.widgets.events.ClickEvent;
@@ -116,9 +117,21 @@
      * @param e The click event.
      */
     public void onClick(ClickEvent e) {
-        Data[] data = getData();
+        List<String> errors = validate();
+        if (errors == null || errors.isEmpty()) {
+            Data[] data = getData();
+            fireStepForwardEvent(new StepForwardEvent(data));
+        }
+        else {
+            StringBuilder sb = new StringBuilder();
 
-        fireStepForwardEvent(new StepForwardEvent(data));
+            for (String error: errors) {
+                sb.append(error);
+                sb.append("<br>");
+            }
+
+            SC.warn(sb.toString());
+        }
     }
 
 
@@ -216,6 +229,11 @@
     }
 
 
+    public List<String> validate() {
+        return new ArrayList<String>();
+    }
+
+
     /**
      * This method needs to be implemented by concrete subclasses. It should
      * create a new Canvas object with a representation of <i>data</i>.