c# - How to convert a view into a PNG? -

i want create png view. using code:

//i instance user control             ucformtoprintview miviewtoprint = new ucformtoprintview();             miviewtoprint.datacontext = ((ucformtoprintview)ccform).datacontext;              //i use rendertargetbitmap render user control             system.windows.media.imaging.rendertargetbitmap rtb = new system.windows.media.imaging.rendertargetbitmap(794, 1122, 72, 72, system.windows.media.pixelformats.pbgra32);             rtb.render(miviewtoprint);              //i use encoder create png             system.windows.media.imaging.pngbitmapencoder encoder = new system.windows.media.imaging.pngbitmapencoder();             encoder.frames.add(system.windows.media.imaging.bitmapframe.create(rtb));               //i use dialog select path save png file             microsoft.win32.savefiledialog savefiledialog = new microsoft.win32.savefiledialog();              savefiledialog.filterindex = 1;              if (savefiledialog.showdialog() == true)             {                  using (system.io.stream stream = savefiledialog.openfile())                 {                      encoder.save(stream);                      stream.close();                      system.diagnostics.process.start(savefiledialog.filename);                 }             } 

the result empty png.

how can create png file user control?

thank much.

the usercontrol has laid out @ least once visible. can achieve calling measure , arrange methods.

var miviewtoprint = new ucformtoprintview(); miviewtoprint.datacontext = ((ucformtoprintview)ccform).datacontext;  // layout, i.e. measure , arrange miviewtoprint.measure(new size(double.positiveinfinity, double.positiveinfinity)); miviewtoprint.arrange(new rect(miviewtoprint.desiredsize));  ...  if (savefiledialog.showdialog() == true) {     using (var stream = savefiledialog.openfile())     {         encoder.save(stream);     }      system.diagnostics.process.start(savefiledialog.filename); }