Android開發 報錯: xxx does not have a NavController set on xxx

問題

在Activity的onCreate生命周期里執行下列代碼,導致 xxx does not have a NavController set on xxx 報錯

布局:

    <androidx.fragment.app.FragmentContainerView
        android:id="@+id/fragment"
        android:layout_width="0dp"
        android:layout_height="0dp"
        android:name="androidx.navigation.fragment.NavHostFragment"
        app:defaultNavHost="true"
        app:navGraph="@navigation/snake_settings_nav"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintLeft_toRightOf="@id/settings"
        app:layout_constraintRight_toRightOf="parent"
        app:layout_constraintTop_toBottomOf="@id/titleLayout" />

代碼:

    private NavController mController;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        mBinding = SnakeActivitySettingsBinding.inflate(getLayoutInflater());
        setContentView(mBinding.getRoot());
        mController = Navigation.findNavController(SettingsActivity.this, R.id.fragment);

    }

問題原因

問題原因就是在onCreate生命周期里FragmentContainerView對應的NavController未構建成功.

 

解決方法

方式一:

很簡單直接onStart生命周期里獲取NavController,如下代碼:

 

    @Override
    protected void onStart() {
        super.onStart();
        mController = Navigation.findNavController(SettingsActivity.this, R.id.fragment);
    }

 

或者,將獲取NavController的任務放到view創建測繪完成后在執行

        mBinding.fragment.post(new Runnable() {
            @Override
            public void run() {
                mController = Navigation.findNavController(SettingsActivity.this, R.id.fragment);
            }
        });

方式二:

使用getSupportFragmentManager獲取

       NavHostFragment navHostFragment = (NavHostFragment) getSupportFragmentManager().findFragmentById(R.id.fragment);
        mController = navHostFragment.getNavController();

 

 

 

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