Magisk/app/src/main/java/com/topjohnwu/magisk/WelcomeActivity.java

package com.topjohnwu.magisk;

import android.os.Bundle;
import android.os.Handler;
import android.support.annotation.NonNull;
import android.support.design.widget.NavigationView;
import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentTransaction;
import android.support.v4.view.GravityCompat;
import android.support.v4.widget.DrawerLayout;
import android.support.v7.app.ActionBarDrawerToggle;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.Toolbar;
import android.view.MenuItem;
import android.view.View;

import com.topjohnwu.magisk.ui.LogFragment;
import com.topjohnwu.magisk.ui.ModulesFragment;
import com.topjohnwu.magisk.ui.RootFragment;

import butterknife.BindView;
import butterknife.ButterKnife;

public class WelcomeActivity extends AppCompatActivity implements NavigationView.OnNavigationItemSelectedListener {

    private static final String SELECTED_ITEM_ID = "SELECTED_ITEM_ID";
    private final Handler mDrawerHandler = new Handler();

    @BindView(R.id.toolbar) Toolbar toolbar;
    @BindView(R.id.drawer_layout) DrawerLayout drawer;
    @BindView(R.id.nav_view) NavigationView navigationView;

    @Override
    protected void onCreate(final Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_welcome);
        ButterKnife.bind(this);

        setSupportActionBar(toolbar);

        ActionBarDrawerToggle toggle = new ActionBarDrawerToggle(this, drawer, toolbar, R.string.navigation_drawer_open, R.string.navigation_drawer_close) {
            @Override
            public void onDrawerOpened(View drawerView) {
                super.onDrawerOpened(drawerView);
                super.onDrawerSlide(drawerView, 0); // this disables the arrow @ completed state
            }

            @Override
            public void onDrawerSlide(View drawerView, float slideOffset) {
                super.onDrawerSlide(drawerView, 0); // this disables the animation
            }
        };

        drawer.setDrawerListener(toggle);
        toggle.syncState();

        navigationView.setNavigationItemSelectedListener(this);

        if (savedInstanceState != null) {
            mDrawerHandler.removeCallbacksAndMessages(null);
            mDrawerHandler.postDelayed(new Runnable() {
                @Override
                public void run() {
                    navigate(savedInstanceState.getInt(SELECTED_ITEM_ID));
                }
            }, 250);
        }

    }

    @Override
    public void onBackPressed() {
        if (drawer.isDrawerOpen(GravityCompat.START)) {
            drawer.closeDrawer(GravityCompat.START);
        } else {
            super.onBackPressed();
        }
    }

    @Override
    public boolean onNavigationItemSelected(@NonNull final MenuItem menuItem) {
        menuItem.setChecked(true);
        mDrawerHandler.removeCallbacksAndMessages(null);
        mDrawerHandler.postDelayed(new Runnable() {
            @Override
            public void run() {
                navigate(menuItem.getItemId());
            }
        }, 250);

        drawer.closeDrawer(GravityCompat.START);
        return true;
    }

    private void navigate(final int itemId) {
        Fragment navFragment = null;
        switch (itemId) {
            case R.id.root:
                setTitle(R.string.root);
                navFragment = new RootFragment();
                break;
            case R.id.modules:
                setTitle(R.string.modules);
                navFragment = new ModulesFragment();
                break;
            case R.id.log:
                setTitle(R.string.log);
                navFragment = new LogFragment();
                break;
        }

        if (navFragment != null) {
            FragmentTransaction transaction = getSupportFragmentManager().beginTransaction();
            transaction.setCustomAnimations(R.anim.fade_in, R.anim.fade_out);
            try {
                transaction.replace(R.id.content_frame, navFragment).commit();
            } catch (IllegalStateException ignored) {
            }
        }
    }
}