wpf - Why do I need to call Dispatcher.BeginInvoke() to allow a visual to properly bind before printing? -


i have usercontrol fixed size of 850x1100 give me same aspect ratio letter-sized piece of paper. display in window inside viewbox, , acts print preview. control inherits window's datacontext, , when it's displayed on screen, bindings work , looks wonderful.

i've written code below in window's code behind (i feel it's totally view-oriented operation) attempt print it. if execute code written, control prints, not appear data bound.

private void printbutton_click(object sender, routedeventargs e) {     var dlg = new printdialog();     var result = dlg.showdialog();     if (result == null || !(bool)result)         return;      var page = new inspectionformprintview { datacontext = this.datacontext };      page.measure(new size(dlg.printableareawidth, dlg.printableareaheight));     page.arrange(new rect(new point(0, 0), page.desiredsize));      dlg.printvisual(page, "inspection form"); }

if modify last line in method to

dispatcher.begininvoke(new action(() => dlg.printvisual(page, "inspection form")), dispatcherpriority.applicationidle, null);

it print fine. why this?

as mentioned lpl in comments, required because wpf needs perform data bindings. since wpf operations queued on dispatcher, need queue print operation complete after dispatcherpriority.databind. therefore, calling begininvoke dispatcherpriority.render or lower give wpf time process bindings on control, show in printed output.


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