我已经构建了一个简单的应用程序，包括 FloatingActionButton 和一个 Snackbar . 当用户点击晶圆厂，实际日期应显示在应用程序的主要内容。
不幸的是，当我点击晶圆厂只有snackbar的工作。 ListItems 什么也看不出来。
我的代码怎么了？
mainactivity.java:

public class MainActivity extends AppCompatActivity {
    ArrayList<String> listItems = new ArrayList<String>();
    ArrayAdapter<String> adapter;
    private ListView myListView;

    @Override
    protected  void onStart() {
        super.onStart();
        myListView = findViewById(R.id.listView);
        adapter = new ArrayAdapter<>(this, android.R.layout.simple_list_item_1, listItems);
        myListView.setAdapter(adapter);
    }

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Toolbar toolbar = findViewById(R.id.toolbar);
        setSupportActionBar(toolbar);

        FloatingActionButton fab = findViewById(R.id.fab);
        fab.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                addListItem();
                Snackbar.make(view, "Item added to list", Snackbar.LENGTH_LONG)
                        .setAction("Action", null).show();
            }
        });
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.menu_main, 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);
    }

    private void addListItem(){
        SimpleDateFormat dateFormat = new SimpleDateFormat("HH:mm:ss MM/dd/yyyy", Locale.US);
        listItems.add(dateFormat.format(new Date()));
        adapter.notifyDataSetChanged();
    }
}

它的xml：

<?xml version="1.0" encoding="utf-8"?>
<androidx.coordinatorlayout.widget.CoordinatorLayout 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"
    tools:context=".MainActivity">

    <com.google.android.material.appbar.AppBarLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:theme="@style/Theme.FabExample.AppBarOverlay">

        <androidx.appcompat.widget.Toolbar
            android:id="@+id/toolbar"
            android:layout_width="match_parent"
            android:layout_height="?attr/actionBarSize"
            android:background="?attr/colorPrimary"
            app:popupTheme="@style/Theme.FabExample.PopupOverlay" />

    </com.google.android.material.appbar.AppBarLayout>

    <include layout="@layout/content_main" />

    <com.google.android.material.floatingactionbutton.FloatingActionButton
        android:id="@+id/fab"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="bottom|end"
        android:layout_margin="@dimen/fab_margin"
        app:srcCompat="@drawable/ic_add_entry" />

</androidx.coordinatorlayout.widget.CoordinatorLayout>

片段的java:

public class FirstFragment extends Fragment {

    @Override
    public View onCreateView(
        LayoutInflater inflater, ViewGroup container,
        Bundle savedInstanceState) {
        // Inflate the layout for this fragment
        return inflater.inflate(R.layout.fragment_first, container, false);
    }

    public void onViewCreated(@NonNull View view, Bundle savedState) {
        super.onViewCreated(view, savedState);
    }
}

片段的xml:

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout 
    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"
    tools:context=".FirstFragment">

    <ListView
        android:id="@+id/listView"
        android:layout_width="0dp"
        android:layout_height="0dp"
        tools:layout_editor_absoluteX="117dp"
        tools:layout_editor_absoluteY="332dp" />

</androidx.constraintlayout.widget.ConstraintLayout>