android - 工具栏在布局中不可见

Question

下面是我的布局，运行时toolbar根本不可见，tabview上的两个tab占据了整个屏幕。在 AndroidStudio 的预览中，我确实看到了 ActionBar，因为我希望它位于顶部。我错过了什么？

<RelativeLayout
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:id="@+id/c">


<android.support.v7.widget.Toolbar
    android:id="@+id/my_toolbar2"
    android:layout_height="wrap_content"
    android:layout_width="fill_parent"

    android:background="?attr/colorPrimary"
    android:layout_marginBottom="10dp"
    app:theme="@style/ThemeOverlay.AppCompat.Dark.ActionBar"

    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto" />


<RelativeLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:id="@+id/c2">


<android.support.design.widget.TabLayout
            android:layout_height="match_parent"
            android:layout_width="match_parent"
            android:id="@+id/tabs"
            app:layout_scrollFlags="scroll|enterAlways"/>
    </RelativeLayout>




<android.support.v4.view.ViewPager xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:id="@+id/pager"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    </android.support.v4.view.ViewPager>

这是我使用此布局的 Activity :

public class TabletGallery extends AppCompatActivity implements ActionBar.TabListener {
 @Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);    //To change body of overridden methods use File | Settings | File Templates.
    setContentView(R.layout.tablet_gallery);

    // Initilization

    toolbar = (Toolbar) findViewById(R.id.my_toolbar2);
    setSupportActionBar(toolbar);
    viewPager = (ViewPager) findViewById(R.id.pager);
    mAdapter = new TabsPagerAdapter(getSupportFragmentManager());
    viewPager.setAdapter(mAdapter);
    TabLayout tabLayout = (TabLayout) findViewById(R.id.tabs);
    tabLayout.setupWithViewPager(viewPager);
    tabLayout.addTab(tabLayout.newTab().setText("Tab 1"));
    tabLayout.addTab(tabLayout.newTab().setText("Tab 2"));

Answer 1

改为使用 LinearLayout 作为根布局。

<LinearLayout
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
android:orientation="vertical"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:id="@+id/c">


<android.support.v7.widget.Toolbar
    android:id="@+id/my_toolbar2"
    android:layout_height="wrap_content"
    android:layout_width="fill_parent"

    android:background="?attr/colorPrimary"
    android:layout_marginBottom="10dp"
    app:theme="@style/ThemeOverlay.AppCompat.Dark.ActionBar"

    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto" />

 <android.support.design.widget.TabLayout
            android:layout_height="match_parent"
            android:layout_width="match_parent"
            android:id="@+id/tabs"
            app:layout_scrollFlags="scroll|enterAlways"/>


<RelativeLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:id="@+id/c2">

    <android.support.v4.view.ViewPager xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:id="@+id/pager"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    </android.support.v4.view.ViewPager>

    </RelativeLayout>






</LinearLayout>