How to disable UP in Navigation for some fragment with the new Navigation Architecture Component?

First, add attributes app:popUpTo='your_nav_graph_id' and app:popUpToInclusive="true" to the action tag.

<fragment
    android:id="@+id/signInFragment"
    android:name="com.glee.incog2.android.fragment.SignInFragment"
    android:label="fragment_sign_in"
    tools:layout="@layout/fragment_sign_in" >
    <action
        android:id="@+id/action_signInFragment_to_usersFragment"
        app:destination="@id/usersFragment"
        app:launchSingleTop="true"
        app:popUpTo="@+id/main_nav_graph"
        app:popUpToInclusive="true" />
</fragment>

Second, navigate to the destination, using the above action as parameter.

findNavController(fragment).navigate(SignInFragmentDirections.actionSignInFragmentToUserNameFragment())

NOTE: If you navigate using method navigate(@IdRes int resId), you won't get the desired result. Hence, I used method navigate(@NonNull NavDirections directions).

WARNING: clearTask has been deprecated and will be remove in future release, not sure what the solution is. Please follow this issue for now to keep up to date

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Oh after 10 minutes finally found the key: use clearTask.

All I have to do is add app:clearTask="true" to that specific action, or use .navigate(R.id.actionXXXX, null, NavOptions.Builder().setClearTask(true).build()), and it's done. Just make sure you add it to all the children of SplashFragment (in this case, both MainFragment and SignUpFragment).

This worked for me in alpha05 release. Add app:popUpTo="@id/nav_graph" in the action tag(inside your nav_graph.xml file). Here "@id/nav_graph is the id of my graph or also called as the Root.

<navigation xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:id="@+id/nav_graph"
app:startDestination="@id/startFragment">
.......
<action
android:id="@+id/action_startFragment_to_homeFragment"
app:destination="@id/homeFragment" 
app:popUpTo="@id/nav_graph"/>
.......

You can also do this in design tab:- select "SplashFragment" and select the action you want to change and then pick "root" for "Pop To"