使用NavigationDrawer按下返回按钮时，直接移到主片段

Question

我在NavigationDrawer中遇到问题。 无论我当前位于哪个片段上，我都想在按下“后退”按钮时移至第一个片段。我在NavigationDrawer中有4个片段。 我还添加了addToBackStack() ，但是它遍历了我之前打开的所有片段。 我已经看到很多与此相关的问题，但是没有一个有用的问题。 这是我的代码：

public class MainActivity extends AppCompatActivity
    implements NavigationView.OnNavigationItemSelectedListener {

    Fragment fragment = null;
    static Toolbar toolbar;

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

        FragmentManager fragmentManager = getSupportFragmentManager();
        FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction();
        fragment = new ContentMainActivity();
        fragmentTransaction.add(R.id.containerView, fragment).commit();

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

    @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) {
        getMenuInflater().inflate(R.menu.main, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        int id = item.getItemId();
        if (id == R.id.action_about) {
            return true;
        }
        return super.onOptionsItemSelected(item);
    }

    @SuppressWarnings("StatementWithEmptyBody")
    @Override
    public boolean onNavigationItemSelected(MenuItem item) {
        int id = item.getItemId();

        if (id == R.id.nav_home) {
            fragment = new ContentMainActivity();
        } else if (id == R.id.nav_batches) {
            fragment = new ViewBatches();
        } else if (id == R.id.nav_view_students) {
            fragment = new ViewAllStudents();
        } else if (id == R.id.nav_fee) {
            fragment = new FeePayments();
        }

        FragmentTransaction fragmentTransaction = getSupportFragmentManager().beginTransaction();
        fragmentTransaction.replace(R.id.containerView, fragment).addToBackStack(null).commit();

        DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
        drawer.closeDrawer(GravityCompat.START);
        return true;
    }
    ...
}

Answer 1

我终于设法解决了。 我没有使用backstack。 我只使用了导航抽屉的方法作为解决方案。 这是我的代码，供那些可能遇到相同问题的人使用：

public class MainActivity extends AppCompatActivity
    implements NavigationView.OnNavigationItemSelectedListener {

Fragment fragment = null;
static Toolbar toolbar;
NavigationView navigationView;

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

    FragmentManager fragmentManager = getSupportFragmentManager();
    FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction();
    fragment = new ContentMainActivity();
    fragmentTransaction.replace(R.id.containerView, fragment).commit();

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

@Override
public void onBackPressed() {
    DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
    if (drawer.isDrawerOpen(GravityCompat.START)) {
        drawer.closeDrawer(GravityCompat.START);
    } else {
        if (checkNavigationMenuItem() != 0)
        {
            navigationView.setCheckedItem(R.id.nav_home);
            fragment = new ContentMainActivity();
            getSupportFragmentManager().beginTransaction().replace(R.id.containerView, fragment).commit();
        }
        else
            super.onBackPressed();
    }
}

private int checkNavigationMenuItem() {
    Menu menu = navigationView.getMenu();
    for (int i = 0; i < menu.size(); i++) {
        if (menu.getItem(i).isChecked())
            return i;
    }
    return -1;
}

@Override
public boolean onCreateOptionsMenu(Menu menu) {
    getMenuInflater().inflate(R.menu.main, menu);
    return true;
}

@Override
public boolean onOptionsItemSelected(MenuItem item) {
    int id = item.getItemId();
    if (id == R.id.action_about) {
        return true;
    }
    return super.onOptionsItemSelected(item);
}

@SuppressWarnings("StatementWithEmptyBody")
@Override
public boolean onNavigationItemSelected(MenuItem item) {
    int id = item.getItemId();

    if (id == R.id.nav_home) {
        fragment = new ContentMainActivity();
    } else if (id == R.id.nav_batches) {
        fragment = new ViewBatches();
    } else if (id == R.id.nav_view_students) {
        fragment = new ViewAllStudents();
    } else if (id == R.id.nav_fee) {
        fragment = new FeePayments();
    }

    FragmentTransaction fragmentTransaction = getSupportFragmentManager().beginTransaction();
    fragmentTransaction.replace(R.id.containerView, fragment).commit();

    DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
    drawer.closeDrawer(GravityCompat.START);
    return true;
}

Answer 2

您可以再尝试一件事。 您只需在onBackPress回调方法中启动所需的片段。 尝试下面的代码并替换为您的代码

@Override
public void onBackPressed() {
fragment = new ContentMainActivity();
FragmentTransaction fragmentTransaction = getSupportFragmentManager().beginTransaction();
fragmentTransaction.replace(R.id.containerView, fragment).addToBackStack(null).commit();
DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
if (drawer.isDrawerOpen(GravityCompat.START)) {
    drawer.closeDrawer(GravityCompat.START);
} else {
    super.onBackPressed();
}

}

我假设ContentMainActivity是您要获取的家庭片段。 您可以在启动主片段时再尝试一件事，然后再添加回栈，否则就不行了。 在这种情况下，如果按“后退”按钮，则后退堆栈中将只有一个片段，它将作为您的主片段并完成。

希望能有所帮助