后退按鈕不會返回上一個片段

Question

我有一個簡單的 android 應用程序，其中啟動器活動是導航抽屜活動。 當用戶單擊任何側邊欄按鈕時，我會顯示幾個片段。 活動首先顯示“fragment1”。

@Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_menu);

        preferences = getSharedPreferences("Settings", 0);

        DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
        ActionBarDrawerToggle toggle = new ActionBarDrawerToggle(
                this, drawer, toolbar, R.string.navigation_drawer_open, R.string.navigation_drawer_close);
        drawer.setDrawerListener(toggle);
        toggle.syncState();

        NavigationView navigationView = (NavigationView) findViewById(R.id.nav_view);
        navigationView.setNavigationItemSelectedListener(this);

        categories fragment = new categories();
        FragmentTransaction fragmenttransaction = getSupportFragmentManager().beginTransaction();
        fragmenttransaction.replace(R.id.frame,fragment,"fragment1");
        fragmenttransaction.commit();

    }

問題是當我移動到此活動中的其他片段並點擊設備上的后退按鈕時，應用程序會立即關閉，而不是返回上一個片段。

我在活動內部的 onBackPressed 函數中嘗試了一些方法，例如“popbackstack”，但這不起作用

  @Override
    public void onBackPressed() {
        DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
        if (drawer.isDrawerOpen(GravityCompat.START)) {
            drawer.closeDrawer(GravityCompat.START);

        }

        if(getFragmentManager().getBackStackEntryCount() > 0){
            getFragmentManager().popBackStackImmediate();
        }

        else{
            super.onBackPressed();
        }

    }

片段類

public class settings extends Fragment {

    SharedPreferences preferences;
    private EditText rangevalue;
    private Button savebtn;

    private int range = 0;
 public settings() {

    }


    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        // Inflate the layout for this fragment
        View v =  inflater.inflate(R.layout.fragment_settings, container, false);

        preferences = getActivity().getSharedPreferences("Settings",0);
        rangevalue = (EditText)v.findViewById(R.id.rangeedittext);
        savebtn = (Button)v.findViewById(R.id.savebutton);

        rangevalue.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {

                range = Integer.parseInt(rangevalue.getText().toString());
            }
        });


        savebtn.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {

                if (range == 0)
                {
                    SharedPreferences.Editor editor = preferences.edit();
                    editor.putInt("Range",2000);
                    editor.apply();
                }
                else
                {
                    SharedPreferences.Editor editor = preferences.edit();
                    editor.putInt("Range",range);
                    editor.apply();
                }
                Toast.makeText(getContext(), "Settings Saved", Toast.LENGTH_SHORT).show();
            }

        });

        return v;

    }

Answer 1

這是因為您沒有將片段添加到 backStack，如果您想檢索后者，請使用此.addToBackStack()將您的片段保存在 backStack 中

 categories fragment = new categories();
        FragmentTransaction fragmenttransaction = getSupportFragmentManager().beginTransaction();
        fragmenttransaction.replace(R.id.frame,fragment,"fragment1");
        fragmenttransaction.addToBackStack().commit();

Answer 2

以這種方式為我工作：

ProfileFragment profile_fragment = new ProfileFragment();

if(getFragmentManager() != null) {
     getFragmentManager()
            .beginTransaction()
            .add(R.id.frame_content, profile_fragment)
            .addToBackStack("back_profile_fragment")
            .commit();

讓 onBackPressed 方法像這樣：

@Override
public void onBackPressed() {
    DrawerLayout drawer = findViewById(R.id.drawer_layout);
    if (drawer.isDrawerOpen(GravityCompat.START)) {
        drawer.closeDrawer(GravityCompat.START);
    } else {
        super.onBackPressed();
    }
}