public class MainActivity extends BaseActivity implements NavigationView.OnNavigationItemSelectedListener,OnFragmentInteractionListener{    public NavigationView navView;    public DrawerLayout drawerLayout;    private Toolbar toolbar;    private ActionBarDrawerToggle toggle;    // 矢量图兼容支持    static {        AppCompatDelegate.setCompatVectorFromResourcesEnabled(true);    }    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_main);        toolbar = (Toolbar) findViewById(R.id.toolbar);        setSupportActionBar(toolbar);        navView = (NavigationView) findViewById( R.id.nav_view );        drawerLayout = (DrawerLayout) findViewById(R.id.drawer_layout);        toggle = new ActionBarDrawerToggle(                this, drawerLayout, toolbar, R.string.navigation_drawer_open, R.string.navigation_drawer_close);        toggle.syncState();        drawerLayout.addDrawerListener(toggle);        getSupportFragmentManager().registerFragmentLifecycleCallbacks(new FragmentManager.FragmentLifecycleCallbacks() {            @Override            public void onFragmentResumed(FragmentManager fm, Fragment f) {                super.onFragmentResumed(fm, f);                if(f instanceof MineFragment) {                    getSupportActionBar().setTitle("我的");                }else if(f instanceof GetHelpFragment){                    getSupportActionBar().setTitle("提供帮助");                }else if(f instanceof HelpFragment) {                    getSupportActionBar().setTitle("帮助");                }else if(f instanceof SettingFragment) {                    getSupportActionBar().setTitle("设置");                }            }        }, false);        //ActionBar的返回按钮监听        toggle.setToolbarNavigationClickListener(new View.OnClickListener() {            @Override            public void onClick(View view) {                getSupportFragmentManager().popBackStack();            }        });        navView.setNavigationItemSelectedListener( this );        initFragment();    }    private void initFragment() {        FragmentTransaction ft = getSupportFragmentManager().beginTransaction();        ft.replace( R.id.content, new MineFragment());        ft.commit();    }    @Override    public boolean onNavigationItemSelected(@NonNull MenuItem item) {        switch (item.getItemId()){            case R.id.nav_mine://我的                switchTo(new MineFragment());                break;            case R.id.nav_get_help://获得帮助                switchTo(new GetHelpFragment());                break;            case R.id.nav_help://提供帮助                switchTo(new HelpFragment());                break;            case R.id.nav_setting://设置                switchTo(new SettingFragment());                break;        }        return true;    }    private void switchTo(Fragment fragment) {        FragmentTransaction ft = getSupportFragmentManager().beginTransaction();        ft.replace( R.id.content, fragment);        ft.commit();        drawerLayout.closeDrawers();    }    @Override    public void onFragmentInteraction(Uri uri) {    }}