How to handle Back Button to remove current fragment In MvvmCross

问题

My MainMenu is the first launched activity or page which will show the MainPage as the Fragment

in this MainMenu,

a) it has a Left Drawer. When user click on an item in the drawer, it will be displayed as fragment.

In this MainPage,
b) it has dropdown menu in Action-Bar. when user click an item in the menu it will be displayed as fragment

The Problem:

1) User click an item in MainPage(b) :Action_bar dropdown menu, how to remove or not to show this current display fragment WHEN user click the back button and show the main page content

I tried below code, it does not work

public override void OnBackPressed()
{
  if (DrawerLayout != null && DrawerLayout.IsDrawerOpen(GravityCompat.Start))

        DrawerLayout.CloseDrawers();
  else
        base.OnBackPressed();
}

回答1:

You can add the fragment to the backstack of the fragment manager with this:

var ft = SupportFragmentManager.BeginTransaction();
ft.AddToBackStack(fragInfo.Tag);
ft.Commit();

I would recommend looking into the Android sample of MvvmCross. It handles a lot of things by default, like the backstack. https://github.com/MvvmCross/MvvmCross-AndroidSupport/tree/master/Samples

回答2:

To add fragment to backstack it is possible to specify AddToBackStack = true in MvxFragmentPresentation attribute:

[MvxFragmentPresentation(typeof(YourViewModel), Resource.Id.your_content_frame, AddToBackStack = true)]

来源：https://stackoverflow.com/questions/32286428/how-to-handle-back-button-to-remove-current-fragment-in-mvvmcross