从导航抽屉中的另一个片段返回到主页片段

Question

在我的应用程序中，我创建了一个包含六个片段的导航抽屉。主选项片段不包括在导航项菜单列表中。现在我想激活移动设备上的"后退"按钮以重定向到主片段。例如，如果我有片段A，B，C，D，E，F，现在如果我单击B，那么如果我按后退按钮，它将返回A。同样，如果我在片段 E 上按后退按钮，它将重定向到片段 A。现在，我如何在代码中实现此逻辑。因此，我尝试了网站上的大量代码，但没有一个工作。这是我的导航抽屉代码

private NavigationView navigationView;
private DrawerLayout drawerLayout;
private Toolbar toolbar ;
private View navigationHeader;
private ImageView imgProfile;
private TextView txtName, txtWebsite;
// flag to load home fragment when user presses back key
private boolean shouldLoadHomeFragOnBackPress = true;
private Handler mHandler;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
toolbar = (Toolbar) findViewById(R.id.toolbar);
setSupportActionBar(toolbar);
mHandler = new Handler();
drawerLayout = (DrawerLayout) findViewById(R.id.drawer_layout);
navigationView = (NavigationView) findViewById(R.id.nav_view);
// Navigation view header
navigationHeader= navigationView.getHeaderView(0);
txtName = navigationHeader.findViewById(R.id.username);
txtWebsite = navigationHeader.findViewById(R.id.email);
imgProfile = navigationHeader.findViewById(R.id.profile_image);
// load nav menu header data
loadNavHeader();
//Set the Home Fragment initially
OptionMenuFragment fragment = new OptionMenuFragment();
android.support.v4.app.FragmentTransaction fragmentTransaction =
getSupportFragmentManager().beginTransaction();
fragmentTransaction.replace(R.id.fragment_container, fragment, "OptionMenuFragment");
fragmentTransaction.commit();
ActionBarDrawerToggle toggle = new ActionBarDrawerToggle(
this, drawerLayout, toolbar, R.string.navigation_drawer_open, R.string.navigation_drawer_close);
drawerLayout.setDrawerListener(toggle);
toggle.syncState();
navigationView.setNavigationItemSelectedListener(this);
}
private void loadNavHeader() {
// name, website
txtName.setText("Hallo");
txtWebsite.setText("mail.com");
imgProfile.setImageResource(R.drawable.profile_image);
//ToDo: Image should be uploaded from web
}
String lastFragmentTag;
boolean showingFirstFragment = true;
public void addNewFragment(Fragment fragment, String fragmentTag) {
FragmentManager fragmentManager = getSupportFragmentManager();
FragmentTransaction transaction = fragmentManager.beginTransaction();
if (lastFragmentTag != null) {
Fragment currentFragment = fragmentManager.findFragmentByTag(lastFragmentTag);
transaction.remove(currentFragment);
} else {
Fragment currentFragment = fragmentManager.findFragmentById(R.id.fragment_container);
transaction.hide(currentFragment);
}
transaction.add(R.id.fragment_container, fragment, fragmentTag);
transaction.commit();
lastFragmentTag = fragmentTag;
showingFirstFragment = false;
}
@Override
public void onBackPressed() {
//Here we're gonna remove the last fragment added, and show OptionMenuFragment again
if (!showingFirstFragment)
{
FragmentManager fragmentManager = getSupportFragmentManager();
FragmentTransaction transaction = fragmentManager.beginTransaction();
Fragment firstFragment = fragmentManager.findFragmentByTag("OptionMenuFragment");
Fragment currentFragment = fragmentManager.findFragmentByTag(lastFragmentTag);
transaction.remove(currentFragment);
transaction.show(firstFragment);
transaction.commit();
showingFirstFragment = true;
} 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.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.blu_home) {
Intent intent = new Intent(this, MainOptionPage.class);
intent.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
startActivity(intent);
return true;
}
return super.onOptionsItemSelected(item);
}

@SuppressWarnings("StatementWithEmptyBody")
@Override
public boolean onNavigationItemSelected(MenuItem item) {
String fragmentTag=null;
// Handle navigation view item clicks here.
Fragment fragment = null;
FragmentManager fragmentManager = getSupportFragmentManager();
switch (item.getItemId()) {
case R.id.view_profile:
fragment = new ViewProfileFragment();
fragmentTag = "ViewProfileFragment";
break;
case R.id.todo_list:
fragment =new ToDoListFragment();
fragmentTag="ToDoListFragment";
break;
case R.id.logout:
showAlertDialogLogOut();
break;
case R.id.settings:
fragment = new SettingsFragment();
fragmentTag="SettingFragment";
break;
case R.id.about:
fragment = new AboutFragment();
fragmentTag="AboutFragment";
break;
case R.id.info:
fragment=new InfoFragment();
fragmentTag="InfoFragment";
break;
}
if(fragment!=null){
fragmentManager.beginTransaction().replace(R.id.fragment_container, fragment).commit();
}
drawerLayout = (DrawerLayout) findViewById(R.id.drawer_layout);
drawerLayout.closeDrawer(GravityCompat.START);
return true;
}
private void showAlertDialogLogOut() {
AlertDialog.Builder builder = new AlertDialog.Builder(this);
builder.setTitle("Logout");
builder.setMessage("Are you sure you want to log out?");
builder.setPositiveButton("YES", new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog, int which) {
// close the dialog, go to login page
dialog.dismiss();
startActivity(new Intent(MainOptionPage.this, LoginPage.class));
}
});
builder.setNegativeButton("NO", new DialogInterface.OnClickListener() {
@Override
public void onClick(DialogInterface dialog, int which) {
// Do nothing
dialog.dismiss();
}
});
AlertDialog alert = builder.create();
alert.show();
}
}

Answer 1

对于这种方法，您需要使用 add(containerViewId， fragment，tag) 方法而不是 replace(containerViewId， fragment)，因为在添加新片段之前，replace 会对之前添加到容器中的所有片段调用 remove(Fragment)。此外，您将需要使用addToBackStack(name)。

这是我为一个项目创建的方法，并为您进行了一些修改：

String lastFragmentTag;
boolean showingFirstFragment = true;
public void addNewFragment(Fragment fragment, String fragmentTag) {
FragmentManager fragmentManager = getSupportFragmentManager();
FragmentTransaction transaction = fragmentManager.beginTransaction();
if (lastFragmentTag != null) {
Fragment currentFragment = fragmentManager.findFragmentByTag(lastFragmentTag);
transaction.remove(currentFragment);
} else {
Fragment currentFragment = fragmentManager.findFragmentById(R.id.fragment_container);
transaction.hide(currentFragment);
}
transaction.add(R.id.fragment_container, fragment, fragmentTag);
transaction.commit();
lastFragmentTag = fragmentTag;
showingFirstFragment = false;
}

然后，您只需要在NavigationItemSelected中进行此更改：

Fragment fragment = null;
FragmentManager fragmentManager = getSupportFragmentManager();
String fragmentTag;
switch (item.getItemId()) {
case R.id.view_profile:
fragment = new ViewProfileFragment();
fragmentTag = "ViewProfileFragment";
break;
...
}
if(fragment!=null){
addNewFragment(fragment, fragmentTag);
}

其中"fragmentTag"将是一个字符串变量，您可以根据实例化的片段进行更改。

编辑：由于代码未按预期工作，因此进行了更多更改：

@Override
public void onBackPressed() {
//Here we're gonna remove the last fragment added, and show OptionMenuFragment again
if (!showingFirstFragment)
{
FragmentManager fragmentManager = getSupportFragmentManager();
FragmentTransaction transaction = fragmentManager.beginTransaction();
Fragment firstFragment = fragmentManager.findFragmentByTag("OptionMenuFragment");
Fragment currentFragment = fragmentManager.findFragmentByTag(lastFragmentTag);
transaction.remove(currentFragment);
transaction.show(firstFragment);
transaction.commit();
showingFirstFragment = true;
} else {
super.onBackPressed();
}
}

添加 OptionMenuFragment 时，请改为执行以下操作：

fragmentTransaction.replace(R.id.fragment_container, fragment, "OptionMenuFragment");