单击底部菜单时如何打开侧面导航抽屉？

Question

This is what i'm trying to achieve

I want settings menu click will appear side nav drawer

HomeActivity.java

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

    mMainFrame  =   (FrameLayout) findViewById(R.id.main_frame);
    mMainNav    =   (BottomNavigationView) findViewById(R.id.main_nav);

    homeFragment         =   new HomeFragment();
    analyticsFragment    =   new AnalyticsFragment();
    paymentFragment      =   new PaymentFragment();
    settingsFragment     =   new SettingsFragment();

    drawerLayout = findViewById(R.id.drawerlayout);

    FragmentManager fragmentManager = getSupportFragmentManager();
    FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction();
    fragmentTransaction.replace(R.id.main_frame,new HomeFragment()).commit();

    mMainNav.setOnNavigationItemSelectedListener(new BottomNavigationView.OnNavigationItemSelectedListener() {
        @Override
        public boolean onNavigationItemSelected(@NonNull MenuItem menuItem) {

            switch (menuItem.getItemId()) {
                case R.id.navigation_home:
                    setFragment(homeFragment);
                    return true;

                case R.id.navigation_analytics:
                    setFragment(analyticsFragment);
                    return true;

                case R.id.navigation_payment:
                    setFragment(paymentFragment);
                    return true;

                case R.id.navigation_settings:
                    drawerLayout.openDrawer(GravityCompat.END);
                    return true;

                default:
                    return false;
            }
        }
    });

    BottomNavigationView navView = findViewById(R.id.main_nav);
    navView.setItemIconTintList(null);

And this is the error i get

Unable to start activity ComponentInfo{com.example.ewallet/com.example.ewallet.HomeActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'android.view.View android.app.Activity.findViewById(int)' on a null object reference

EDIT : I tried to paste some of my code here but StackOverflow error too many code to post

Answer 1

You didn't bind your object correctly and caused a NullPointerException.

Please paste your code and we can help you.

I saw a weird part, but maybe this error will still appear, you may need to paste your layout.xml

mMainNav    =   (BottomNavigationView) findViewById(R.id.main_nav);


BottomNavigationView navView = findViewById(R.id.main_nav);
navView.setItemIconTintList(null);

Should be modify to

mMainNav.setItemIconTintList(null);

You can check if it is null with

getActivity().findViewById(R.id.XXX)

UPDATE

    drawerLayout = (DrawerLayout)getView().findViewById(R.id.drawerlayout);

    case R.id.navigation_settings:
                drawerLayout.openDrawer(drawerLayout);
                return true;

Answer 2

Took me 4 days to figure this out. Turned out you need to have drawerlayout in your activity layout. My problem was drawerlayout from different xml that's why returned null. Thx for those who tried for helping me

<?xml version="1.0" encoding="utf-8"?>
<android.support.v4.widget.DrawerLayout 
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:id="@+id/drawer_layout"
android:fitsSystemWindows="true"
tools:openDrawer="end">

    <include
        layout="@layout/app_bar_settings"
        android:layout_width="match_parent"
        android:layout_height="match_parent" />

    <android.support.design.widget.NavigationView
        android:id="@+id/nav_view"
        android:layout_width="wrap_content"
        android:layout_height="match_parent"
        android:layout_gravity="end"
        android:fitsSystemWindows="true"
        app:headerLayout="@layout/nav_header_settings"
        app:menu="@menu/activity_settings_drawer" />

<android.support.constraint.ConstraintLayout
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:id="@+id/container"
    tools:context=".HomeActivity">

    <FrameLayout
        android:id="@+id/main_frame"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:layout_marginBottom="56dp">

    </FrameLayout>

    <android.support.design.widget.BottomNavigationView
        android:id="@+id/main_nav"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:layout_marginStart="0dp"
        android:layout_marginEnd="0dp"
        android:background="?android:attr/windowBackground"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        app:labelVisibilityMode="labeled"
        app:itemTextColor="@color/colorPrimaryDark"
        app:menu="@menu/bottom_nav_menu" />
    </android.support.constraint.ConstraintLayout>

</android.support.v4.widget.DrawerLayout>