How to set FileExt with DzExporter?

578276864_563542692c

my code:

DzExportMgr *emgr= dzApp->getExportMgr();
DzExporter *oExporter = emgr->getExporter(m_totalQuads);
DzFileIOSettings * oSettings = new DzFileIOSettings();

oSettings->setStringValue( "Preset", "3DS MAX (1 unit = 1cm)" );

oSettings->setFloatValue( "Scale", 1 );
oSettings->setStringValue( "LatAxis", "X" );
oSettings->setStringValue( "VertAxis", "Y" );
oSettings->setStringValue( "DepthAxis", "Z" );
oSettings->setBoolValue( "InvertLat", false );
oSettings->setBoolValue( "InvertVert", false );
oSettings->setBoolValue( "InvertDepth", false );
oSettings->setBoolValue( "IgnoreInvisible", false );
oSettings->setBoolValue( "WeldSeams", false );
oSettings->setBoolValue( "RemoveUnusedVerts", false );
oSettings->setBoolValue( "WriteVT", true );
oSettings->setBoolValue( "WriteVN", true );
oSettings->setBoolValue( "WriteO", false );

oSettings->setBoolValue( "WriteG", true );
oSettings->setBoolValue( "GroupGeom", true );
oSettings->setBoolValue( "GroupNodes", false );
oSettings->setBoolValue( "GroupSurfaces", false );
oSettings->setBoolValue( "GroupSingle", true );

oSettings->setBoolValue( "WriteUsemtl", false );
oSettings->setBoolValue( "WriteMtllib", false );
oSettings->setBoolValue( "CollectMaps", false );
oSettings->setBoolValue( "ConvertMaps", false );

oSettings->setBoolValue( "SelectedOnly", true );
oSettings->setBoolValue( "SelectedRootsOnly", true );
oSettings->setBoolValue( "PrimaryRootOnly", false );
oSettings->setBoolValue( "IncludeParented", false );

oSettings->setIntValue( "RunSilent", 1 );

oExporter->writeFile(filePath,oSettings);

I don't know why DzExporter not export .obj file but with aother fileExtension,How can I set extension with DzExporter class,or DzFileIOSettings(I can't find a completed docmentment about how to set DzFileIOSettings).
Thanks!

578276864_563542692c

Problem solved,Thanks!