java - Android - Fragment 未替换

Question

我的应用程序中有一个底部导航，我想做的是在单击底部导航 View 按钮时加载不同的 fragment 。

但是当我单击另一个按钮时，当前 fragment 不会替换为另一个 fragment 。

查看函数 OnNavigationItemSelected(在开关盒内)。我给出了两个 fragment ，但是单击按钮没有任何区别。

请帮忙!预先感谢😊

这是我的代码:

public class MainActivity extends AppCompatActivity {

//code for the things are populated when the activity is created
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    //creating teh tool bar
    Toolbar customToolbar = findViewById(R.id.customToolbar);
    setSupportActionBar(customToolbar);

    //creating the fragments view
    //checking for the fragment container
    if(findViewById(R.id.fragment_container) != null) {
        // However, if we're being restored from a previous state,
        // then we don't need to do anything and should return or else
        // we could end up with overlapping fragments.
        if (savedInstanceState != null) {
            return;
        }
        //creating the fragment
        LibraryFragment libraryFragment = new LibraryFragment();
        // In case this activity was started with special instructions from an
        // Intent, pass the Intent's extras to the fragment as arguments
        libraryFragment.setArguments(getIntent().getExtras());

        // Add the fragment to the 'fragment_container' FrameLayout
        getSupportFragmentManager().beginTransaction().add(R.id.fragment_container, libraryFragment).commit();
    }
}

//to add menu to the app bar we need to inflate the menu first
@Override
public boolean onCreateOptionsMenu(Menu menu) {
    MenuInflater customMenuInflater = getMenuInflater();
    //if the menu does not work try to restart the android studio after clearing the cache its in the File option
    customMenuInflater.inflate(R.menu.custom_app_bar_menu, menu);
    return  super.onCreateOptionsMenu(menu);
}

//actions when the items on the menu are clicked
//it is incomplete because we have'nt created any activities yet
@Override
public boolean onOptionsItemSelected (MenuItem item) {
    switch (item.getItemId()) {
        case R.id.action_search:
            //open the search bar fragment
            return true;
        case R.id.action_settings:
            //open the settings activity
            return true;
        case R.id.action_account:
            //open the account activity
            return true;
        default:
            //we can't recognise the user action so
            //super class will handel it
            return super.onOptionsItemSelected(item);
    }
}

//Bottom navigation menu actions on the selection of the items
//it will be used to trigger the functions to call the fragments
//to load the fragments in the activity
private BottomNavigationView.OnNavigationItemSelectedListener onNavigationItemSelectedListener = new BottomNavigationView.OnNavigationItemSelectedListener() {
    @Override
    public boolean onNavigationItemSelected(@NonNull MenuItem menuItem) {
        Fragment fragment;
        switch (menuItem.getItemId()) {
            case R.id.navigation_library:
                //Library fragment
                loadFragment(new LibraryFragment());
                return true;
            case R.id.navigation_for_you:
                //ForYou fragment
                loadFragment(new ForYouFragment());
                return true;
            case R.id.navigation_browse:
                //ignore this for the moment
                return  true;
            case R.id.navigation_radio:
                //ignore this for the moment
                return  true;
            default:
                //ignore this for the moment
                return false;
        }
    }
};

//function to load the fragment into the fragment container
public void loadFragment(Fragment fragment) {
    FragmentTransaction transaction = getSupportFragmentManager().beginTransaction();
    transaction.replace(R.id.fragment_container, fragment);
    transaction.commit();
}
}

Answer 1

这对我有用:

public class MainActivity extends AppCompatActivity {

//code for the things are populated when the activity is created
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    //creating teh tool bar
    Toolbar customToolbar = findViewById(R.id.customToolbar);
    setSupportActionBar(customToolbar);

    //creating the fragments view
    //checking for the fragment container
    if(findViewById(R.id.fragment_container) != null) {
        loadFragment(new LibraryFragment());
    }

    //Bottom navigation menu actions on the selection of the items
    //it will be used to trigger the functions to call the fragments
    //to load the fragments in the activity

    BottomNavigationView navigation = findViewById(R.id.navigation);
    navigation.setOnNavigationItemSelectedListener(new BottomNavigationView.OnNavigationItemSelectedListener() {
        @Override
        public boolean onNavigationItemSelected(@NonNull MenuItem menuItem) {
            int id = menuItem.getItemId();
            if(id == R.id.navigation_library) {
                loadFragment(new LibraryFragment());
            }
            else if (id == R.id.navigation_for_you) {
                loadFragment(new ForYouFragment());
            }
            return false;
        }
    });

}

//to add menu to the app bar we need to inflate the menu first
@Override
public boolean onCreateOptionsMenu(Menu menu) {
    MenuInflater customMenuInflater = getMenuInflater();
    //if the menu does not work try to restart the android studio after clearing the cache its in the File option
    customMenuInflater.inflate(R.menu.custom_app_bar_menu, menu);
    return  super.onCreateOptionsMenu(menu);
}

//actions when the items on the menu are clicked
//it is incomplete because we have'nt created any activities yet
@Override
public boolean onOptionsItemSelected (MenuItem item) {
    switch (item.getItemId()) {
        case R.id.action_search:
            //open the search bar fragment
            return true;
        case R.id.action_settings:
            //open the settings activity
            return true;
        case R.id.action_account:
            //open the account activity
            return true;
        default:
            //we can't recognise the user action so
            //super class will handel it
            return super.onOptionsItemSelected(item);
    }
}

//function to load the fragment into the fragment container
public void loadFragment(Fragment fragment) {
    FragmentTransaction transaction = getSupportFragmentManager().beginTransaction();
    transaction.replace(R.id.fragment_container, fragment);
    transaction.commit();
}
}