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In fragment I want to click back how to show alert dialog

I am using navigation menu in an Activity. When I click menu, it goes to particular fragment that time I give addtobackstack(null). I want to fix these 2 issues:
I want to show do you want to exit app through a popup In the back fragment
Assume that I traverse from Fragment A to B and then B to C. If I give back in the Fragment C I want to come the main page, without showing the Fragment B.
This is my Home Activity:
package school.wyse.app.activities;
import android.app.Activity;
import android.app.AlertDialog;
import android.content.Context;
public class ParentHomeActivity extends AppCompatActivity
implements NavigationView.OnNavigationItemSelectedListener {
ServerUtils servutil;
GridLayoutManager grid;
Toolbar toolbar;
private View navHeader;
LinearLayout profile;
ImageView msglist;
ArrayList<StudentProfile> lang_list_new;
public RecyclerView studentsListRecyclerView;
public ParentMenuDashoard mStudAdapter;
StudentProfile[] profiles;
private StudentProfile[] studentCachedData;
Context ctx;
DrawerLayout drawer;
ImageView imageViewstaff;
String tenent_id,profilename,image,userphone;
Integer id,roleid;
String backStateName;
TextView profile_phone,profile_name;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
try {
setContentView(R.layout.activity_parent_home);
backStateName = this.getClass().getName();
ctx=this;
Toast.makeText(ctx, "backStateName--"+backStateName, Toast.LENGTH_SHORT).show();
toolbar = (Toolbar) findViewById(R.id.toolbar);
setSupportActionBar(toolbar);
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);
navHeader=navigationView.getHeaderView(0);
studentsListRecyclerView = (RecyclerView) navHeader.findViewById(R.id.messageWindowRecycler);
ParentDashboard parentDashboard = new ParentDashboard();
FragmentManager manager = getSupportFragmentManager();
manager.beginTransaction().replace(R.id.content_frame, parentDashboard, parentDashboard.getTag()).commit();
toolbar.setTitle("Dashboard");
} catch (Exception e) {
e.printStackTrace();
}
}
#Override
public void onBackPressed() {
try {
DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
if (drawer.isDrawerOpen(GravityCompat.START)) {
drawer.closeDrawer(GravityCompat.START);
} else {
super.onBackPressed();
}
} catch (Exception e) {
e.printStackTrace();
}
}
#Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.home, 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_msg) {
return true;
}*/
return super.onOptionsItemSelected(item);
}
#SuppressWarnings("StatementWithEmptyBody")
#Override
public boolean onNavigationItemSelected(MenuItem item) {
// Handle navigation view item clicks here.
int id = item.getItemId();
if (id == R.id.nav_dashboard) {
ParentDashboard parentDashboard = new ParentDashboard();
FragmentManager manager = getSupportFragmentManager();
manager.beginTransaction().replace(R.id.content_frame, parentDashboard, parentDashboard.getTag()).addToBackStack(null).commit();
//toolbar.setTitle("Dashboard");
} else if (id == R.id.nav_teachers) {
TeacherList teacherList = new TeacherList();
FragmentManager manager = getSupportFragmentManager();
// manager.beginTransaction().replace(R.id.id_content_frame, accountsMenuListFragment, "AccountsMenu").addToBackStack(" ").commit();
manager.beginTransaction().replace(R.id.content_frame, teacherList, teacherList.getTag()).addToBackStack(null).commit();
// toolbar.setTitle("Teachers");
} else if (id == R.id.nav_attendance) {
AttendanceFragment attendanceFragment = new AttendanceFragment();
FragmentManager manager = getSupportFragmentManager();
manager.beginTransaction().replace(R.id.content_frame, attendanceFragment, attendanceFragment.getTag()).addToBackStack(null).commit();
// toolbar.setTitle("Attendance");
} else if (id == R.id.nav_consumablity) {
ParentConsumablityFragment parentConsumablityFragment = new ParentConsumablityFragment();
FragmentManager manager = getSupportFragmentManager();
manager.beginTransaction().replace(R.id.content_frame, parentConsumablityFragment, parentConsumablityFragment.getTag()).addToBackStack(null).commit();
// toolbar.setTitle("Attendance");
}
else {
}
DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
drawer.closeDrawer(GravityCompat.START);
return true;
}
}

Okay, sorry for late reply
This part goes in onBackPressed() of your activity, which basically check if you have fragments attached (so it won't perform the native back, which closes the app)
if (childFragments.size() > 0) {
if (childFragments.get((childFragments.size() - 1)) != null) {
childFragments.remove(childFragments.size() - 1);
return;
}
}
All you have to do is add/remove items to this array every time you attach / detach fragments :)
For your particular case when you are on fragment C and want to go back to fragment A without showing fragment B, I suggest you make a public function that remove all fragments from ArrayList except last one (from position 0)

Use below code in mainactivity where you want to show appexit:
#Override
public void onBackPressed() {
if (doubleBackToExitPressedOnce) {
super.onBackPressed();
finish();
return;
}
this.doubleBackToExitPressedOnce = true;
Toast.makeText(this, "Please click BACK again to exit", Toast.LENGTH_SHORT).show();
new Handler().postDelayed(new Runnable() {
#Override
public void run() {
doubleBackToExitPressedOnce = false;
}
}, 2000);
}
When moving fragment A to B do not add "addbackstack". When moving fragment B to C add "addbackstack("C")"

first of all, you have to take care of your second issue as it will lead to easy handle for the first issue, hence you have to take care of how to initiate the fragments in order to always coming to the first fragment while hitting back regardless the flow of fragments that lead to the current fragment, to do so, just initiate the fragments like the following:
/**
* To initiate any fragment
*/
private void showAnyFragment(Fragment fragmentToShow) {
getSupportFragmentManager().popBackStack();
FrameLayout frameLayout = (FrameLayout) findViewById(R.id.content);
frameLayout.setVisibility(View.VISIBLE);
getSupportFragmentManager().beginTransaction()
.replace(R.id.content, fragmentToShow)
.addToBackStack(null)
.commit();
}
/**
* When (for a reason) you want to initiate the main fragment (FragmentA)
*/
private void homeClicked() {
getSupportFragmentManager().popBackStack();
}
Now, fragmentA is your main fragment, when going from A to B to C to D and click back button it will go back to A directly.
Coming to your second issue, it will be straight forward as you already keeping only fragmentA always in the back stack, so onBackPressed() function of the Activity will not be called unless there are No other fragment other than FragmentAis being displayed(e.g if you are in fragmentC and you click back button, the onBackPressed() function will not be called), so you are sure that when you come inside onBackPressed() function of the activity that the currently running fragment is FragmentA which is your main page fragment.
so if you want to display a popup while the user trying to exit the app (he would be in FragmentA and hiitting Back), all you have to do is to override the onBackPressed() method of the MainActivity that holds the fragments:
#Override
public void onBackPressed() {
// the user here is in FragmentA(main page),
and he is clicking back to exit the app.
// TODO show popup here or do whatever you want
}

Fragment to fragment communication within a NavigationDrawer

In my app, I have a NavigationDrawer in my app that has two fragments I want to display (Fragment1 and Fragment2) in a MainActivity. I have a menu item in my ToolBar in Fragment 1 when clicked I want to my MainActivity to switch to Fragment2 and have the NavigationView reflect the UI changes.
public class MainActivity extends AppCompatActivity {
private DrawerLayout mDrawer;
private Toolbar toolbar;
private NavigationView nvDrawer;
private ActionBarDrawerToggle drawerToggle;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
if (savedInstanceState == null) {
getSupportFragmentManager().beginTransaction().replace(R.id.flContent, new BookListFragment()).commit();
}
// Set a Toolbar to replace the ActionBar.
toolbar = (Toolbar) findViewById(R.id.toolbar);
setSupportActionBar(toolbar);
// Find our drawer view
mDrawer = (DrawerLayout) findViewById(R.id.drawer_layout);
drawerToggle = setupDrawerToggle();
// Tie DrawerLayout events to the ActionBarToggle
mDrawer.addDrawerListener(drawerToggle);
// Find our drawer view
nvDrawer = (NavigationView) findViewById(R.id.nvView);
// Setup drawer view
setupDrawerContent(nvDrawer);
}
#Override
protected void onPostCreate(Bundle savedInstanceState) {
super.onPostCreate(savedInstanceState);
// Sync the toggle state after onRestoreInstanceState has occurred.
drawerToggle.syncState();
}
#Override
public void onConfigurationChanged(Configuration newConfig) {
super.onConfigurationChanged(newConfig);
// Pass any configuration change to the drawer toggles
drawerToggle.onConfigurationChanged(newConfig);
}
private ActionBarDrawerToggle setupDrawerToggle() {
// NOTE: Make sure you pass in a valid toolbar reference. ActionBarDrawToggle() does not require it
// and will not render the hamburger icon without it.
return new ActionBarDrawerToggle(this, mDrawer, toolbar, R.string.drawer_open, R.string.drawer_close);
}
private void setupDrawerContent(NavigationView navigationView) {
navigationView.setNavigationItemSelectedListener(
new NavigationView.OnNavigationItemSelectedListener() {
#Override
public boolean onNavigationItemSelected(MenuItem menuItem) {
selectDrawerItem(menuItem);
return true;
}
});
}
public void selectDrawerItem(MenuItem menuItem) {
// Create a new fragment and specify the fragment to show based on nav item clicked
Fragment fragment = null;
Class fragmentClass;
switch (menuItem.getItemId()) {
case R.id.book_list_fragment:
fragmentClass = BookListFragment.class;
break;
case R.id.discover_fragment:
fragmentClass = DiscoverFragment.class;
break;
default:
fragmentClass = BookListFragment.class;
}
try {
fragment = (Fragment) fragmentClass.newInstance();
} catch (Exception e) {
e.printStackTrace();
}
// Insert the fragment by replacing any existing fragment
FragmentManager fragmentManager = getSupportFragmentManager();
fragmentManager.beginTransaction().replace(R.id.flContent, fragment).commit();
// Highlight the selected item has been done by NavigationView
menuItem.setChecked(true);
// Set action bar title
setTitle(menuItem.getTitle());
// Close the navigation drawer
mDrawer.closeDrawers();
}
#Override
public boolean onOptionsItemSelected(MenuItem item) {
// The action bar home/up action should open or close the drawer.
switch (item.getItemId()) {
case android.R.id.home:
mDrawer.openDrawer(GravityCompat.START);
return true;
}
if (drawerToggle.onOptionsItemSelected(item)) {
return true;
}
return super.onOptionsItemSelected(item);
}
}
Fragment Code
public class BookListFragment extends Fragment {
...
#Override
public boolean onOptionsItemSelected(MenuItem item) {
switch (item.getItemId()) {
case R.id.action_insert_dummy_data:
insertBook();
return true;
case R.id.action_delete_all_entries:
int rowsDeleted = getContext().getContentResolver().delete(ShelfHelpContract.BookEntry.CONTENT_URI, null, null);
return true;
case R.id.action_discover:
/*TODO Here I want to open another Fragment and have it reflect
in the UI on my NavigationView and MainActivity
*/
return true;
}
return super.onOptionsItemSelected(item);
....
}

The following code takes care of replacing your Fragment when the user clicks on one of the navigation items
// Insert the fragment by replacing any existing fragment
FragmentManager fragmentManager = getSupportFragmentManager();
fragmentManager.beginTransaction().replace(R.id.flContent, fragment).commit();
Besides replacing the fragment you will want to also update the title of your activity using something along the lines of:
((AppCompatActivity)getActivity()).getSupportActionBar().setTitle("Home");
And finally you must tell your NavigationView to highlight the right item using the setChecked(boolean) function. It should look something like this:
nvDrawer.getMenu().findItem(/*your item id*/).setChecked(true);
If you want to perform the same action when the user clicks on a menu item then make sure to add a new case to the switch block found in your onOptionsItemSelected(MenuItem item) and just call the same lines passing in the right Fragment

How to hide navigation drawer item while the respective fragment is opened

In my app, I used navigation drawer. Here I listed all the items.
From the image,the items are,
Home
Filter & Sort
WishList
Shop
MyOrder
Settings
LogOut
If I am in the Fragment of Shop , I need to hide it. How to do this?
Please help me.

You can handle it in fragments onAttach method. Set the visibility of perticular item according to your need.
#Override
public void onAttach(Context context) {
super.onAttach(context);
YourActivity activity = (YourActivity)context;
NavigationView navigationView = (NavigationView) activity.findViewById(R.id.yournavigationviewid);
navigationView.getMenu().findItem(R.id.youritemid).setVisible(false);
}

inside your setNavigationItemSelectedListener where you get the selected menuItem, you can implement the code. Also you require to store the instance of the hidden menu item to make it visible later
MenuItem prevMenuItem;
navigationView.setNavigationItemSelectedListener(new NavigationView.OnNavigationItemSelectedListener() {
#Override
public boolean onNavigationItemSelected(MenuItem menuItem) {
if(prevMenuItem != null) prevMenuItem.setVisible(true) //making visible the previously hidden item.
menuItem.setVisible(false);
prevMenuItem = menuItem //storing the instance of currently hidden item to make it visible later.
return true;
}
});

In your public onNavigationItemSelected(MenuItem item) if you are setting one fragment then automatically drawer will hide. I'm doing like this :
public boolean onNavigationItemSelected(MenuItem item) {
// Handle navigation view item clicks here.
toolbar.setTitle(item.toString());
int id = item.getItemId();
if (id == R.id.dashboard) {
fragment = new DashboardFragment();
} else if (id == R.id.manage_users) {
}else{
}
setFragmentLayout(fragment);
return true;
}
Set your fragment according to your requirements.

You can hide the drawer using mDrawerLayout.closeDrawers() in onNavigationItemSelected Listener like this:
mNavigationView.setNavigationItemSelectedListener(new NavigationView.OnNavigationItemSelectedListener() {
#Override
public boolean onNavigationItemSelected(MenuItem menuItem) {
menuItem.setChecked(true);
switch (menuItem.getItemId()) {
case R.id.navigation_item_shop:
//do your stuffs or attach fragment
mDrawerLayout.closeDrawers();
return true;
default:
return true;
}
}
}

on the fragments overide the onAttach method. Set the visibility of for items your don't need.
#Override
public void onAttach(Context context) {
super.onAttach(context);
MainActivity activity = (MainActivity)context;
NavigationView navigationView = (NavigationView) activity.findViewById(R.id.navmenu);
// hide the menu items not related to this fragment
Menu m = navigationView.getMenu();
m.findItem(R.id.first).setVisible(false);
m.findItem(R.id.second).setVisible(false);
m.findItem(R.id.therd).setVisible(false);
//and so on
}

Why setContentView doesn't disappear when changing fragment

I have a navigation drawer and when I click on one of the menus, I want the default content to disappear, but it just doesn't happen and when I click on a new menu it's still there.
This is really annoying, I've been trying to find solution the whole day and I'm going crazy now.
Please help me out, if you can. Thanks in advance!
I copy the whole code here. (p.s.: this is the first and last time I'm programming on Android, this is a nightmare...I just must do this now :/)
public class About extends AppCompatActivity {
private Toolbar toolbar;
private NavigationView navigationView;
private DrawerLayout drawerLayout;
ImageButton FAB;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_about);
FAB = (ImageButton) findViewById(R.id.imageButton);
FAB.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
Intent i = new Intent(About.this, SecondActivity.class);
startActivity(i);
//FAB click, call other thing...
}
});
navigationView = (NavigationView) findViewById(R.id.nav_view);
FragmentTransaction fragmentTransaction = getSupportFragmentManager().beginTransaction();
fragmentTransaction.replace(R.id.content_frame, new ListViewFragment());
fragmentTransaction.commit();
setNavDrawer();
navigationView.setCheckedItem(R.id.nav_gallery);
}
private void setNavDrawer() {
// Initializing Toolbar and setting it as the actionbar
toolbar = (Toolbar) findViewById(R.id.toolbar);
setSupportActionBar(toolbar);
//Initializing NavigationView
//Setting Navigation View Item Selected Listener to handle the item click of the navigation menu
navigationView.setNavigationItemSelectedListener(new NavigationView.OnNavigationItemSelectedListener() {
// This method will trigger on item Click of navigation menu
#Override
public boolean onNavigationItemSelected(MenuItem menuItem) {
//Checking if the item is in checked state or not, if not make it in checked state
if (menuItem.isChecked()) menuItem.setChecked(false);
else menuItem.setChecked(true);
//Closing drawer on item click
drawerLayout.closeDrawers();
//Check to see which item was being clicked and perform appropriate action
switch (menuItem.getItemId()) {
//Replacing the main content with ContentFragment Which is our Inbox View;
case R.id.nav_camera:
Toast.makeText(getApplicationContext(), "Clicked", Toast.LENGTH_SHORT).show();
ContentFragment fragment = new ContentFragment();
android.support.v4.app.FragmentTransaction f = getSupportFragmentManager().beginTransaction();
f.replace(R.id.content_frame, fragment);
f.commit();
return true;
// For rest of the options we just show a toast on click
case R.id.nav_gallery:
Toast.makeText(getApplicationContext(), "Whatever", Toast.LENGTH_SHORT).show();
UserFragment fragment2 = new UserFragment();
android.support.v4.app.FragmentTransaction f2 = getSupportFragmentManager().beginTransaction();
f2.replace(R.id.content_frame, fragment2);
f2.commit();
return true;
case R.id.nav_slideshow:
Toast.makeText(getApplicationContext(), "SOON", Toast.LENGTH_SHORT).show();
return true;
case R.id.nav_share:
Toast.makeText(getApplicationContext(), "SOON", Toast.LENGTH_SHORT).show();
return true;
default:
Toast.makeText(getApplicationContext(), "SOON", Toast.LENGTH_SHORT).show();
return true;
}
}
});
drawerLayout = (DrawerLayout) findViewById(R.id.drawer_layout);
ActionBarDrawerToggle actionBarDrawerToggle = new ActionBarDrawerToggle(this,drawerLayout,toolbar,R.string.navigation_drawer_open, R.string.navigation_drawer_close){
#Override
public void onDrawerClosed(View drawerView) {
// Code here will be triggered once the drawer closes as we dont want anything to happen so we leave this blank
super.onDrawerClosed(drawerView);
}
#Override
public void onDrawerOpened(View drawerView) {
// Code here will be triggered once the drawer open as we dont want anything to happen so we leave this blank
super.onDrawerOpened(drawerView);
}
};
//Setting the actionbarToggle to drawer layout
drawerLayout.addDrawerListener(actionBarDrawerToggle);
//calling sync state is necessay or else your hamburger icon wont show up
actionBarDrawerToggle.syncState();
}
#Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.about, 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);
}
}

Use these code on menu click..
Fragment fragment = new ContentFragment();
FragmentManager fragmentManager = getActivity().getSupportFragmentManager();
FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction();
fragmentTransaction.replace(R.id.content_frame, fragment);
fragmentTransaction.remove(new CurrentFragment());
fragmentTransaction.addToBackStack(null);
fragmentTransaction.commit();
an also add these lines in xml
<FrameLayout
android:id="#+id/frame_container"
android:layout_width="match_parent"
android:layout_height="match_parent"
/>

Try this
Fragment fragment = new Fragment();
fragment.setRetainInstance(true);
fragment = new ContentFragment ();
FragmentManager fragmentManager = getFragmentManager();
fragmentManager.beginTransaction()
.replace(R.id.content_frame, fragment)
.commit();

How to select the first item in a navigation drawer and open a fragment on application start

I have created MainActivity with NavigationView. When Activity is opened I want to automatically select the first item in the navigation drawer and open Fragment under that item. I've searched a lot but didn't find any proper solutions.
What is the proper way to do this ?
Main Activity:
public class MainActivity extends AppCompatActivity implements Config {
private NavigationView navigationView;
private DrawerLayout drawerLayout;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
setSupportActionBar(toolbar);
toolbar.setTitleTextColor(getResources().getColor(R.color.colorIcons));
if (null != getSupportActionBar())
getSupportActionBar().setLogo(R.drawable.ic_blogger_white);
//Start PostListFragmentWebView
/*PostListFragmentWebView postListFragmentWebView = new PostListFragmentWebView();
getSupportFragmentManager().beginTransaction()
.replace(R.id.frame, postListFragmentWebView)
.commit();*/
//Initializing NavigationView
navigationView = (NavigationView) findViewById(R.id.navigationView);
//Setting Navigation View Item Selected Listener to handle the item click of the navigation menu
navigationView.setNavigationItemSelectedListener(new NavigationView.OnNavigationItemSelectedListener() {
#Override
public boolean onNavigationItemSelected(MenuItem menuItem) {
//Checking if the item is in checked state or not, if not set it to checked state.
if (menuItem.isChecked()) menuItem.setChecked(false);
else menuItem.setChecked(true);
//Closing drawer on item click
drawerLayout.closeDrawers();
//Check to see which item was clicked and perform the appropriate action.
switch (menuItem.getItemId()) {
case R.id.posts:
PostListFragmentWebView postListFragment = new PostListFragmentWebView();
getSupportFragmentManager().beginTransaction()
.replace(R.id.frame, postListFragment)
.commit();
return true;
case R.id.pages:
PageListFragmentWebView pagetListFragment = new PageListFragmentWebView();
getSupportFragmentManager().beginTransaction()
.replace(R.id.frame, pagetListFragment)
.commit();
return true;
case R.id.blog:
BlogInfoFragmentWebView blogInfoFragment = new BlogInfoFragmentWebView();
getSupportFragmentManager().beginTransaction()
.replace(R.id.frame, blogInfoFragment)
.commit();
return true;
default:
Toast.makeText(getApplicationContext(), getResources().getString(R.string.drawer_error), Toast.LENGTH_SHORT).show();
return true;
}
}
});
// Initializing Drawer Layout and ActionBarToggle
drawerLayout = (DrawerLayout) findViewById(R.id.drawerLayout);
ActionBarDrawerToggle actionBarDrawerToggle = new ActionBarDrawerToggle(this, drawerLayout, toolbar, R.string.open_drawer, R.string.close_drawer) {
#Override
public void onDrawerClosed(View drawerView) {
// Code here will be triggered once the drawer closes as we don't want anything to happen so we leave this blank.
super.onDrawerClosed(drawerView);
}
#Override
public void onDrawerOpened(View drawerView) {
// Code here will be triggered once the drawer open as we dont want anything to happen so we leave this blank.
super.onDrawerOpened(drawerView);
}
};
//Setting the actionbarToggle to drawer layout
drawerLayout.setDrawerListener(actionBarDrawerToggle);
drawerLayout.getChildAt(0).setSelected(true);
//calling sync state is necessary or else your hamburger icon wont show up
actionBarDrawerToggle.syncState();
}
}

In onCreate(), following code will load the first item's fragment upon first start:
if (savedInstanceState == null) {
navigationView.getMenu().performIdentifierAction(R.id.posts, 0);
}
Thanks to calvinfly for this comment.

Add android:checked="true" to your first menu item.
And manually select one item, using
getSupportFragmentManager().beginTransaction().replace(R.id.frame, postListFragment).commit();
to open fragment.

Instead of normal listener ...
navView.setNavigationItemSelected(new Navigation.View.OnNavigationItemSelectedListener() {bla, bla, bla})
Create the listener as an Obj:
NavigationView.OnNavigationItemSelectedListener navViewListener;
navView.setNavigationItemSelectedListener(navViewListener = new NavigationView.OnNavigationItemSelectedListener() {bla, bla, bla})
...and use the Obj to trigger the listener event:
navViewListener.onNavigationItemSelected(navView.getMenu().getItem(0));
...where getItem(0) is the first menu item.
Use a method getItem(0).setChecked(true) or android:checked="true" at its menu item XML definition.

You could also use navigationView.setCheckedItem(R.id.default)(javadoc) after you setup your navigationview.

just add this code in onCreate method:
FragmentTransaction ftrans = getFragmentManager().beginTransaction();
ftrans.replace(R.id.container, <yourfragment>).commit();
Work for me !

This can be done even better while considering orientation and other configuration changes. We could select whatever nav drawer menuitem depending on whether we are coming from a previous state. Check: For the Navigation drawer wielding Activity:-
public static final String SELECTED_NAV_MENU_KEY = "selected_nav_menu_key";
// The selected grid position
private int mSelectedNavMenuIndex = 0;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_demo);
...........................................................
navigationView.setNavigationItemSelectedListener(this);
if (savedInstanceState != null) {
// Recover assets
mSelectedNavMenuIndex = savedInstanceState.getInt(SELECTED_NAV_MENU_KEY);
// Recover menu as selected
MenuItem menuItem = navigationView.getMenu().getItem(mSelectedNavMenuIndex);
toggleNavMenuItemCheck(menuItem);
navigationView.getMenu().performIdentifierAction(menuItem.getItemId(), mSelectedNavMenuIndex);
return;
} else {
MenuItem menuItem = navigationView.getMenu().getItem(mSelectedNavMenuIndex);
toggleNavMenuItemCheck(menuItem);
navigationView.getMenu().performIdentifierAction(menuItem.getItemId(), mSelectedNavMenuIndex);
}
}
The toggle method that helps uncheck or check the menu item
private void toggleNavMenuItemCheck(MenuItem menuItem) {
if (menuItem.isChecked()){
menuItem.setChecked(false);
} else {
menuItem.setChecked(true);
}
}
This is how I save the state of the selected menu item. Check:-
#Override
public boolean onNavigationItemSelected(MenuItem item) {
int id = item.getItemId();
switch (id) {
case R.id.nav_explore:
showExploreFragment(null);
mSelectedNavMenuIndex = 0;
break;
case R.id.nav_orders:
mSelectedNavMenuIndex = 1;
break;
case R.id.nav_settings:
mSelectedNavMenuIndex = 2;
break;
default:
showExploreFragment(null);
mSelectedNavMenuIndex = 0;
}
drawer.closeDrawer(GravityCompat.START);
return true;
}
// Save any important data for recovery
#Override
protected void onSaveInstanceState(Bundle outState) {
super.onSaveInstanceState(outState);
outState.putInt(SELECTED_NAV_MENU_KEY, mSelectedNavMenuIndex);
}
NB: The line with code:
navigationView.getMenu().performIdentifierAction(menuItem.getItemId(), mSelectedNavMenuIndex);
Can be replaced by the code:
onNavigationItemSelected(menuItem);

in menu.xml remember to mention android:checkable="true" for single item and android:checkableBehavior="single" for a group of items.
<item
android:id="#+id/pos_item_help"
android:checkable="true"
android:title="Help" />
<group
android:id="#+id/group"
android:checkableBehavior="single">
<item
android:id="#+id/menu_nav_home"
android:icon="#drawable/ic_home_black_24dp"
android:title="#string/menu_nav_home" />
</group>
then inside NavigationItemSelectedListener use setCheckedItem(R.id.item_id_in_menu) to make it selected.
#Override
public boolean onNavigationItemSelected(#NonNull MenuItem item) {
switch (item.getItemId()) {
case R.id.pos_item_pos:
navigationView.setCheckedItem(R.id.pos_item_pos);
break;
case R.id.pos_item_orders:
navigationView.setCheckedItem(R.id.pos_item_orders);
break;
default:
}
return true;
}
And you do not have to do the dirty task of managing the selected item anymore. navigationView manages it by self.

1.) To land to the HomeFragment initially, use this inside your onCreate() in MainActivity:
Fragment fragment = new HomeFragment();
// replacing the fragment
if (fragment != null) {
FragmentTransaction ft = getSupportFragmentManager().beginTransaction();
ft.replace(R.id.content_frame, fragment);
ft.commit();
}
2.) To set the item as selected in navigationDrawer set the item as checked in navigation_menu.xml
android:checked = "true"