Question

我想知道为什么当我切换它们时我的片段留在后台。

这个问题似乎非常罕见，它正在谈论后台堆栈。你能解释一下吗？

所以，这是我的代码：

public class MainActivity extends AppCompatActivity
    implements NavigationView.OnNavigationItemSelectedListener {

public FragmentTransaction fragmentTransaction;
public FragmentManager fragmentManager = getFragmentManager();
public Fragment FragmentToDisplay = null;
public static Context cMainActivity;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
    setSupportActionBar(toolbar);

    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.addDrawerListener(toggle);
    toggle.syncState();

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

    cMainActivity = this;
    displaySelectedScreen(R.id.main_layout);
}

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

@Override
public boolean onCreateOptionsMenu(Menu menu) {
    // Inflate the menu; this adds items to the action bar if it is present.
    getMenuInflater().inflate(R.menu.main, menu);
    return true;
}

@Override
public boolean onOptionsItemSelected(MenuItem item) {
    // Handle action bar item clicks here. The action bar will
    // automatically handle clicks on the Home/Up button, so long
    // as you specify a parent activity in AndroidManifest.xml.
    int id = item.getItemId();

    //noinspection SimplifiableIfStatement
    if (id == R.id.action_settings) {
        return true;
    }

    return super.onOptionsItemSelected(item);
}

@SuppressWarnings("StatementWithEmptyBody")
@Override
public boolean onNavigationItemSelected(MenuItem item) {
    displaySelectedScreen(item.getItemId());
    return true;
}

private void displaySelectedScreen(int ItemId){
    if (ItemId == R.id.main_layout){
        FragmentToDisplay = new homeFragment();
    } else if (ItemId == R.id.led_menu) {
        FragmentToDisplay = new ledFragment();
    } else if (ItemId == R.id.pin_menu) {

    } else if (ItemId == R.id.ecran_menu) {

    }

    if (FragmentToDisplay != null) {
        fragmentTransaction = fragmentManager.beginTransaction();
        fragmentTransaction.add(R.id.fragmentLayout, FragmentToDisplay);
        fragmentTransaction.commit();
    }

    DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
    drawer.closeDrawer(GravityCompat.START);
    Log.i("Display something", "Display Home");
}}

这里是我片段的代码：

public class ledFragment extends Fragment{

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
    return inflater.inflate(R.layout.led_layout, container, false);
}

@Override
public void onViewCreated(View view, Bundle savedInstanceState) {
    super.onViewCreated(view, savedInstanceState);
}}

提前致谢！

Answer 1

替换：

fragmentTransaction.add(R.id.fragmentLayout, FragmentToDisplay);

使用：

fragmentTransaction.replace(R.id.fragmentLayout, FragmentToDisplay);

Answer 2

查看Fragments Transactions文档，您可以更好地了解add()和replace()

Answer 3

此方法将片段添加到片段中，剩下的片段继续工作。如果您不想这样做。

if (FragmentToDisplay != null) {
            fragmentTransaction = fragmentManager.beginTransaction();
            fragmentTransaction.replace(R.id.fragmentLayout, FragmentToDisplay);
            fragmentTransaction.commit();
        }

尝试这种方法

{{1}}

为什么片段留在后台？

3 个答案: