android - 在 BottomNavigationView 中按下后退按钮时按钮没有改变

Question

我在底部导航栏的 dashbordActivity 中使用了三个 fragment 。在后退按钮上正确按下前一个 fragment View 但底部导航按钮没有改变。

在我从底部导航中选择个人资料并按后退按钮后，第一张图片中的主页 fragment 已被选中。 fragment 发生变化，但底部导航项没有变化。

这是我的底部导航 View .....

  private BottomNavigationView.OnNavigationItemSelectedListener mOnNavigationItemSelectedListener
        = new BottomNavigationView.OnNavigationItemSelectedListener() {
    @Override
    public boolean onNavigationItemSelected(@NonNull MenuItem item) {

        switch (item.getItemId()) {
            case R.id.navigation_home:
                setTitle("Home");
                fragment = new FirstFragment();
                loadFragment(fragment);
                return true;
            case R.id.navigation_favorite:

                setTitle("favourite");
                fragment = new MyFavoriteAdsFragment();
                loadFragment(fragment);
                return true;
            case R.id.navigation_profile:

                setTitle("Profile");
                fragment = new ProfileFragment();
                loadFragment(fragment);
                return true;
            case R.id.navigation_myads:
                setTitle("Chat");
                fragment = new MyAdsFragment();
                loadFragment(fragment);
                return true;
            case R.id.navigation_chat:
                //   mTextMessage.setText(R.string.title_chat);
                setTitle("Chat");
                fragment = new TabFragmentChatUserList();
                loadFragment(fragment);
              /* Intent i=new Intent(getApplicationContext(),Chat.class);
               startActivity(i);*/
                return true;
        }
        return false;
    }
};


  private void loadFragment(Fragment fragment) {
    // load fragment
     transaction = getSupportFragmentManager().beginTransaction();
    transaction.replace(R.id.frame_container, fragment);
    transaction.addToBackStack("TAG");
    transaction.commit();
  /*  fragmentManager.beginTransaction().replace(R.id.home_container, frag).addToBackStack(null).commit();*/
}

ob back press 我试过了...

   @Override
  public void onBackPressed()
  {

 // if your using fragment then you can do this way
        int fragments 
  =getSupportFragmentManager().getBackStackEntryCount();
        if (fragments == 1) {
            new AlertDialog.Builder(this)
                    .setMessage("Are you sure you want to exit?")
                    .setCancelable(false)
                    .setPositiveButton("Yes", new DialogInterface.OnClickListener() {
                        public void onClick(DialogInterface dialog, int id) {
                            finish();
                        }
                    })
                    .setNegativeButton("No", null)
                    .show();


        } else {
            if (getFragmentManager().getBackStackEntryCount() > 1) {
                getFragmentManager().popBackStack();
                if(navigation.getSelectedItemId () != R.id.navigation_favorite)
                {
                    navigation.setSelectedItemId(R.id.navigation_favorite);
                }
                else if(navigation.getSelectedItemId () != R.id.navigation_chat)
                {
                    navigation.setSelectedItemId(R.id.navigation_chat);
                }
                else if(navigation.getSelectedItemId () != R.id.navigation_profile)
                {
                    navigation.setSelectedItemId(R.id.navigation_profile);
                }
                else
                {
                    super.onBackPressed();
                }

            } else {
                super.onBackPressed();
            }
        }

Answer 1

您需要检查您的后台堆栈并将监听器添加到您的 fragment 管理器，之后根据您的 fragment 您需要根据您的 fragment 设置特定的按钮检查。

fragmentManager.addOnBackStackChangedListener(new FragmentManager.OnBackStackChangedListener() {
        @Override
        public void onBackStackChanged() {
            // If the stack decreases it means I clicked the back button
            if( fragmentManager.getBackStackEntryCount() <= count){
                //check your position based on selected fragment and set it accordingly.
                navigation.getMenu().getItem(your_pos).setChecked(true);
        }
    }
});