我想将抽屉导航功能添加到我的 Activity 中，但左侧的默认菜单图标没有出现，尽管当我向右滑动时，抽屉打开了。这是我的布局文件:

    <?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:id="@+id/drawer_layout"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:fitsSystemWindows="true"
    tools:openDrawer="start">

    <android.support.design.widget.CoordinatorLayout
        android:id="@+id/coordinatorLayout"
        android:layout_width="match_parent"
        android:layout_height="match_parent">

        <android.support.design.widget.AppBarLayout
            android:id="@+id/appBarLayout"
            android:layout_width="match_parent"
            android:theme="@style/AppTheme.AppBarOverlay"
            android:layout_height="wrap_content">

            <android.support.v7.widget.Toolbar
                android:id="@+id/toolbar"
                android:layout_width="match_parent"
                android:layout_height="?attr/actionBarSize"
                android:background="?attr/colorPrimary"
                app:popupTheme="@style/AppTheme.PopupOverlay"
                app:layout_scrollFlags="scroll|enterAlways" />
            <android.support.design.widget.TabLayout
                android:id="@+id/tabLayout"
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                app:tabTextColor="@android:color/white"
                app:tabSelectedTextColor="@android:color/white"
                app:tabIndicatorColor="@android:color/white"
                app:tabIndicatorHeight="6dp"/>
        </android.support.design.widget.AppBarLayout>

        <android.support.v4.view.ViewPager
            android:id="@+id/viewPager"
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            app:layout_behavior="@string/appbar_scrolling_view_behavior"/>
    </android.support.design.widget.CoordinatorLayout>

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

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

我的 Activity 文件:

public class PartThreeActivity extends AppCompatActivity implements NavigationView.OnNavigationItemSelectedListener {


    private DrawerLayout mDrawerLayout;
    private Toolbar toolbar;


    @Override
    protected void onCreate(Bundle savedInstanceState) {
        setTheme(R.style.AppThemeBlue);
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_part_three);

        initToolbar();
        initViewPagerAndTabs();


        DrawerLayout 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);
    }

    private void initToolbar() {
        Toolbar mToolbar = (Toolbar) findViewById(R.id.toolbar);
        setSupportActionBar(mToolbar);
        setTitle(getString(R.string.app_name));
        mToolbar.setTitleTextColor(getResources().getColor(android.R.color.white));
    }

    private void initViewPagerAndTabs() {
        ViewPager viewPager = (ViewPager) findViewById(R.id.viewPager);
        PagerAdapter pagerAdapter = new PagerAdapter(getSupportFragmentManager());
        pagerAdapter.addFragment(PartThreeFragment.createInstance(20), getString(R.string.tab_1));
        pagerAdapter.addFragment(PartThreeFragment.createInstance(4), getString(R.string.tab_2));
        viewPager.setAdapter(pagerAdapter);
        TabLayout tabLayout = (TabLayout) findViewById(R.id.tabLayout);
        tabLayout.setupWithViewPager(viewPager);
    }

    @Override
    public void onBackPressed() {
        DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
        if (drawer.isDrawerOpen(GravityCompat.START)) {
            drawer.closeDrawer(GravityCompat.START);
        } 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.one_more, 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);
    }

    @SuppressWarnings("StatementWithEmptyBody")
    @Override
    public boolean onNavigationItemSelected(MenuItem item) {
        // Handle navigation view item clicks here.
        int id = item.getItemId();

        if (id == R.id.nav_camera) {
            // Handle the camera action
        } else if (id == R.id.nav_gallery) {

        } else if (id == R.id.nav_slideshow) {

        } else if (id == R.id.nav_manage) {

        } else if (id == R.id.nav_share) {

        } else if (id == R.id.nav_send) {

        }

        DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
        drawer.closeDrawer(GravityCompat.START);
        return true;
    }

    static class PagerAdapter extends FragmentPagerAdapter {

        private final List<Fragment> fragmentList = new ArrayList<>();
        private final List<String> fragmentTitleList = new ArrayList<>();

        public PagerAdapter(FragmentManager fragmentManager) {
            super(fragmentManager);
        }

        public void addFragment(Fragment fragment, String title) {
            fragmentList.add(fragment);
            fragmentTitleList.add(title);
        }

        @Override
        public Fragment getItem(int position) {
            return fragmentList.get(position);
        }

        @Override
        public int getCount() {
            return fragmentList.size();
        }
        @Override
        public CharSequence getPageTitle(int position) {
            return fragmentTitleList.get(position);
        }
    }
}

截图如下:

这是我项目的链接: https://drive.google.com/open?id=0B6_hNGJUq8_2RUtxTl9pTGlqb2c 请帮我找出菜单没有出现的原因，谢谢。

最佳答案

您的 toolbar 引用未初始化，因为 Toolbar mToolbar 是一个局部变量，它将无效，因为您在添加时正在使用 toolbar 引用toogle 当前未初始化

改变这个

 private void initToolbar() {
        Toolbar mToolbar = (Toolbar) findViewById(R.id.toolbar);
        setSupportActionBar(mToolbar);
        setTitle(getString(R.string.app_name));
        mToolbar.setTitleTextColor(getResources().getColor(android.R.color.white));
    }

进入这个

 private void initToolbar() {
        toolbar = (Toolbar) findViewById(R.id.toolbar);
        //^^^^ initialize the reference which is being used to add toggle 
        setSupportActionBar(toolbar);
        setTitle(getString(R.string.app_name));
        toolbar.setTitleTextColor(getResources().getColor(android.R.color.white));
    }

关于android - 为什么工具栏中的菜单图标没有出现在 DrawerLayout 中，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/44739575/