how to refresh pdf page after add text

if u coding activity base on PDFView class directly(not use PDFReader class).
a sample ReaderActivity using ReaderController class, is the simplest sample.

sorry, somethink forgot.
end of PDFReader.PDFOpen(), there is 1 line code:
m_view.vOpen(m_doc, 4, back_color, this);
it means PDFReader object shall be listener for PDFView.
and PDFReader class there is a method: when u call PDFView.vRenderAsync, it call listener.OnPDFInvalidate().
this implements from PDFReader class.

i tried this code as in PDFReader class but i am unable to get the PDFReaderListener interface in code as well above method works under ontouch event how can i implement the ontouch event at pdf . ?
PDFPos pos = m_view.vGetPos((int)event.getX(), (int)event.getY());
PDFVPage vpage = m_view.vGetPage(pos.pageno);
Page page = vpage.GetPage();
if( page != null )
{
float pt[] = new float[2];
pt[0] = pos.x;
pt[1] = pos.y;
page.AddAnnotText(pt);//add a text note annotation.
m_view.vRenderSync(vpage);//reflush to backing bitmap.
if( m_listener != null )
m_listener.OnPageModified(vpage.GetPageNo());//display to screen, this is important.
}

now please change the my code . i just want to changes reflect at same time as ink ,rect does .i am just adding text . could you implement the addtext functionality in your demo . i checked your demo RDPDFReader as well PDfreader but i did not not see any adding text or edittext programatically .

please check my code and please modify the code as according to you my code is following..

PageContent content = new PageContent();
content.Create();//create content, do not forget.
content.GSSave();
Matrix mat = new Matrix( 1, 1, 100, 500 );
content.GSSetMatrix(mat);
mat.Destroy();

Page page = doc.GetPage(currentpage_num);

Document.DocFont dfont = doc.NewFontCID("DroidSansFallback", 1 | ;//bold and embed in horizontal writing
ResFont rfont = page.AddResFont(dfont);

content.TextBegin();
content.TextSetFont(rfont, 20);//set font and size
content.SetFillColor(0xff9801);
content.SetStrokeColor(0x10);
content.TextSetCharSpace(0);
content.TextSetWordSpace(0.3f);
content.TextSetLeading(20);
content.TextSetRenderMode(2);//fill and stroke
content.TextSetHScale(120);//set horizontal scale
content.DrawText(getDate());
content.TextEnd();
content.GSRestore();
PDFView pdf= new PDFView(getApplicationContext());
PDFViewVert view = new PDFViewVert(getApplicationContext());
view.vSetPageAlign(1);
pdf=view;
pdf.vOpen(doc, currentpage_num, 0xFFCCCC, pdfviewlistner);
PDFVPage vpage = pdf.vGetPage(currentpage_num);
pdf.vRenderAsync(vpage);
please help