IllegalStateException: Link does not have a NavController set

问题

I'm using Android Navigation Component for Navigation. I have a LoginFragment which has a button to transition to SignUpFragment. On clicking the button I'm getting this error.

java.lang.IllegalStateException: View android.support.v7.widget.AppCompatButton{49d9bd1 VFED..C.. ...P.... 201,917-782,1061 #7f090172 app:id/signUpLink} does not have a NavController set

Here is my nav_graph.xml

<navigation xmlns:app="http://schemas.android.com/apk/res-auto"
        xmlns:android="http://schemas.android.com/apk/res/android"
        xmlns:tools="http://schemas.android.com/tools"
        app:startDestination="@id/loginFragment">
        <fragment
            android:id="@+id/loginFragment"
            android:name="org.fossasia.openevent.app.core.auth.login.LoginFragment"
            android:label="login_fragment"
            tools:layout="@layout/login_fragment">
            <action
                android:id="@+id/action_loginFragment_to_signUpFragment"
                app:destination="@id/signUpFragment" />

        </fragment>
    </navigation>

Here is the code in LoginFragment for Navigation -

binding.signUpLink.setOnClickListener(Navigation.createNavigateOnClickListener(R.id.action_loginFragment_to_signUpFragment, null));

Here is extract from activity layout file for NavHostFragment -

<FrameLayout
            android:id="@+id/fragment_container"
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            app:layout_behavior="@string/appbar_scrolling_view_behavior"
            android:name="android.navigation.fragment.NavHostFragment"
            app:navGraph="@navigation/main_navigation"
            app:defaultNavHost="true"/>

回答1:

Actually, Navigation can't find NavController in FrameLayout. So replacing <FrameLayout> with <fragment> will do fine.

Remember to add

android:name="android.navigation.fragment.NavHostFragment"

inside <fragment> tag.

After changes it will look similar to this -

 <fragment
       android:id="@+id/fragment_container"
       android:layout_width="match_parent"
       android:layout_height="match_parent"
       app:layout_behavior="@string/appbar_scrolling_view_behavior"
       android:name="android.navigation.fragment.NavHostFragment"
       app:navGraph="@navigation/main_navigation"
       app:defaultNavHost="true"/>

回答2:

Make sure that the home fragment in activity has name parameter set to:

android:name="androidx.navigation.fragment.NavHostFragment"

for example:

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical">

    <fragment
        android:id="@+id/navigationHost"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:name="androidx.navigation.fragment.NavHostFragment"
        app:defaultNavHost="true"
        app:navGraph="@navigation/cycle_count_navigation" />

</RelativeLayout>

回答3:

Use the view of fragment such as onViewCreated

 override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
    super.onViewCreated(view, savedInstanceState)

    val navController = Navigation.findNavController(view)

    binding.signUpLink.setOnClickListener {
            navController.navigate(R.id.action_loginFragment_to_signUpFragment)
    }

回答4:

I faced the same problem. So,instead of this,

binding.signUpLink.setOnClickListener(Navigation.createNavigateOnClickListener(R.id.action_loginFragment_to_signUpFragment, null));

I used my navhost fragment to find the navcontroller:

Button button = (Button)findViewById(R.id.button);

    button.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {

            Fragment navhost = getSupportFragmentManager().findFragmentById(R.id.fragment2);
            NavController c = NavHostFragment.findNavController(navhost);
            c.navigate(R.id.firstFragment);


        }
    });

fragment2 is my navhostfragmentID.

来源：https://stackoverflow.com/questions/50502269/illegalstateexception-link-does-not-have-a-navcontroller-set