Java null pointer exception while getting a segment DFF handle

Question

Hi,
my requirement is to make a field mandatory based upon a dff segment value (Y/N). i override PFR since segment is a poplist on the page (and poplists don't fire any event)
i searched in the "view source" of the page and found that segment id is ActFlexField0
when i click on save button i got "java null pointer exception"
here is code:
public void processFormRequest(OAPageContext oapagecontext, OAWebBean oawebbean) throws OAException
+{+
+//get a handle to AM+
OAApplicationModule am;
am = oapagecontext.getRootApplicationModule();
oapagecontext.writeDiagnostics(this,"Root AM=>"oapagecontext.getApplicationModule(oawebbean).getName() ,1);+
if(oapagecontext.getParameter("applyCreActBut") != null || oapagecontext.getParameter("saveDtlBut") != null)
+{+
+/*Conditional mandatoryness of IdContribuente field*/+
+// first, find the flexfield's handle+
OADescriptiveFlexBean oaDFF;
oaDFF = (OADescriptiveFlexBean)oawebbean.findIndexedChildRecursive("ActFlexField");
+//oaDFF.processFlex(oapagecontext);+
oapagecontext.writeDiagnostics(this, "Niccal: i got DFF handle", 1);
+//oapagecontext.writeDiagnostics(this, "Niccal: oamcb value is:"+oaDFF.getAttributeValue(), 1);+
+/*+
RenderingContext con = (RenderingContext) oapagecontext.getRenderingContext();
Enumeration x= null;
x= oaDFF.getChildNames(con);
oapagecontext.writeDiagnostics(this, "After getChild", 1);
while(x.hasMoreElements())
+{+
String aParamName = (String)x.nextElement();
oapagecontext.writeDiagnostics(this, "Niccal: DFF segment names are:"aParamName, 1);+
+//OAWebBean dffbeans=(OAWebBean)oaDFF.findChildRecursive(aParamName);+
+}+
+//oaDFF.mergeSegmentsWithParent(oapagecontext);+
OAMessageChoiceBean oamcb = (OAMessageChoiceBean)oaDFF.findChildRecursive("ActFlexField0");
+//String sIsForeign = (String)oaDFF.getAttributeValue("Attribute1");+
+//oapagecontext.writeDiagnostics(this, "Niccal: Attribute1 is:"+sIsForeign, 1);+
oapagecontext.writeDiagnostics(this, "Niccal: before if", 1);it's urgent
any help appreciated
thanx
N

Answer 1

hi Keerthi,
thank you.
i tried with below code but still unsuccesfully
     +     oaDFF = (OADescriptiveFlexBean)oawebbean.findIndexedChildRecursive("ActFlexField");+
oapagecontext.writeDiagnostics(this, "Niccal: i got DFF handle", 1);
OAMessageTextInputBean mtib = (OAMessageTextInputBean)oaDFF.findChildRecursive("ActFlexField0");
oapagecontext.writeDiagnostics(this, "Niccal: before if", 1);
i am able to print 1° comment line but not second. so i think it's something wrong getting the segment handle.
anyway i'm not able to reach your suggested if statement because execution stops before.
Infact, if i comment line :OAMessageTextInputBean mtib = (OAMessageTextInputBean)oaDFF.findChildRecursive("ActFlexField0");
page doesn't give error and saves data.
any suggestion appreciated,
thanx,
N