Android Studio打开一个片段，但不更改底部导航菜单状态

Question

我有一个按钮，让我改变片段，它成功地做到了这一点。我打开了新片段，但底部的导航菜单并没有改变它的样式。这是一个简单的底部导航菜单，因为它是，当您选择当前正在查看的片段时，它会使底部的片段文本变大，图标也变大。这就是问题所在，它不会改变菜单。

goButton = (ImageButton) SOMEView.findViewById(R.id.go_button);
    goButton.setOnClickListener(new View.OnClickListener()   {
        public void onClick(View v)  {
            System.out.println("Started");

            AppCompatActivity mainActivity = new MainActivity();
           ((MainActivity) mainActivity).bottomNavigation.findViewById(R.id.nav_info).callOnClick();
            Fragment nextFragment = new INFOFragment("second");
            FragmentTransaction transaction = getFragmentManager().beginTransaction();
            transaction.replace(R.id.fragment_container, nextFragment );
            transaction.addToBackStack(null);
            transaction.commit();
        }
    });

信息片段：

public class INFOFragment extends Fragment {

public String state;
@SuppressLint("ValidFragment")
public INFOFragment(String state) {
    this.state = state;
}
@Nullable
@Override
public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
    if(state.equals("first")) {
        System.out.println("info");
    return inflater.inflate(R.layout.fragment_info, container, false);
    }
    else {
        System.out.println("second state started");
        return inflater.inflate(R.layout.fragment_another_view, container, false);
    }
}}

主要活动：

public class MainActivity extends AppCompatActivity {
public BottomNavigationView bottomNavigation;
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    bottomNavigation = findViewById(R.id.bnavigation);
    bottomNavigation.setOnNavigationItemSelectedListener(navigationListener);
    getSupportFragmentManager().beginTransaction().replace(R.id.fragment_container, new INFOFragment("first")).commit();
    bottomNavigation.setSelectedItemId(R.id.nav_info);
}

private BottomNavigationView.OnNavigationItemSelectedListener navigationListener =
        new BottomNavigationView.OnNavigationItemSelectedListener() {
            @Override
            public boolean onNavigationItemSelected(@NonNull MenuItem item) {
                Fragment selectedFragment = null;
                switch(item.getItemId()) {
                    case R.id.nav_another_view:
                        System.out.println("vid ovo");
                        selectedFragment = new ANOTHERVIEWFragment();
                        break;
                    case R.id.nav_info:
                        System.out.println("v2id ovo");
                        selectedFragment = new INFOFragment("prvi");
                        break;
                    case R.id.nav_some_view:
                        selectedFragment = new SOMEFragment();
                        break;
                }
                getSupportFragmentManager().beginTransaction().replace(R.id.fragment_container,selectedFragment).commit();
                return true;
            }
        };}

Answer 1

步骤1：在MainActivity上创建一个常量，如下所示

int prev_nav_item = 0;

第2步：

private BottomNavigationView.OnNavigationItemSelectedListener navigationListener =
        new BottomNavigationView.OnNavigationItemSelectedListener() {
            @Override
            public boolean onNavigationItemSelected(@NonNull MenuItem item) {
                Fragment selectedFragment = null;
                switch(item.getItemId()) {
                    case R.id.nav_another_view:
                        System.out.println("vid ovo");
                        selectedFragment = new ANOTHERVIEWFragment();
                        prev_nav_item = 0;
                        break;
                    case R.id.nav_info:
                        System.out.println("v2id ovo");
                        selectedFragment = new INFOFragment("prvi");
                        prev_nav_item = 1;
                        break;
                    case R.id.nav_some_view:
                        selectedFragment = new SOMEFragment();
                        prev_nav_item = 2;
                        break;
                }
                getSupportFragmentManager().beginTransaction().replace(R.id.fragment_container,selectedFragment).commit();
                return true;
            }
        };}

第3步：创建一个函数来更改主活动中的底部菜单位置

public void selectBottomMenu(final int position) {
        Handler uiHandler = new Handler();
        uiHandler.post(new Runnable() {
            @Override
            public void run() {
                bottomNavigation.setCurrentItem(position);
            }
        });
    }

步骤3：从每个片段更新底部菜单位置，如onResume（）中的

@Override
    public void onResume() {
        super.onResume();
        ((MainActivity) mActivity).selectBottomMenu(0); //change value depending on your bottom menu position
    }