c# - UWP on screen back button - how to trigger system back event? -

i have uwp app - design has "back" button in screen content, use trigger system navigation event handled in app.xaml.cs file. current click handler, pasted each file needs is:

frame rootframe = window.current.content frame; if (rootframe.cangoback)     rootframe.goback(); 

how instead trigger event, trigger event handler contains code?

in app.xaml.cs, add onlaunced(...):

protected override void onlaunched(launchactivatedeventargs e) {     ...     if (rootframe == null)     {         ...         // register handler backrequested events         systemnavigationmanager.getforcurrentview().backrequested += this.onbackrequested;     }     ... } 

where in onbackrequested(...), can in app.xaml.cs:

private void onbackrequested(object sender, backrequestedeventargs e) {     frame rootframe = window.current.content frame;      if (rootframe.cangoback)     {         e.handled = true;         rootframe.goback();     } } 

this adapted support multiple frames if implement custom navigation, , can add global handling of showing/hiding button via like:

public void updatebackbutton(frane frame) {     bool cangoback = (frame?.cangoback ?? false);      systemnavigationmanager.getforcurrentview().appviewbackbuttonvisibility = cangoback         ? appviewbackbuttonvisibility.visible         : appviewbackbuttonvisibility.collapsed; } 

you can programmatically call via function in app.xaml.cs or in custom navigation manager:

public bool trygoback(frame frame) {     bool handled = false;      if (frame?.cangoback ?? false)     {         handled = true;         frame.goback();     }      this.updatebackbutton(frame);      return handled; }