Android应用菜单图标不显示问题排查求助

我按照教程开发Android笔记应用，但运行APK时，主布局（activity_main_note.xml）的菜单图标无法显示。以下是相关代码文件，帮忙排查遗漏点：

menu_main_activity.xml #

<?xml version="1.0" encoding="utf-8"?> 
<menu xmlns:android="http://schemas.android.com/apk/res/android" xmlns:app="http://schemas.android.com/apk/res-auto"> 
<!-- NEW NOTE --> 
<item android:id="@+id/action_create" android:enabled="true" android:icon="@android:drawable/ic_menu_add" android:orderInCategory="0" android:title="create" android:visible="true" app:showAsAction="always" /> 
<!-- SETTINGS --> 
<item android:id="@+id/action_settings" android:enabled="true" android:icon="@android:drawable/ic_menu_manage" android:orderInCategory="10" android:title="settings" android:visible="true" app:showAsAction="ifRoom" /> 
</menu>

MainNote.java #

package com.example.lenovo.home; 
import android.content.Context; 
import android.content.Intent; 
import android.os.Bundle; 
import android.support.annotation.IdRes; 
import android.support.v7.app.AppCompatActivity; 
import android.support.v7.widget.CardView; 
import android.view.Menu; 
import android.view.MenuItem; 
import android.view.View; 
import android.widget.AdapterView; 
import android.widget.ListView; 
import android.widget.Toast; 
import java.util.ArrayList; 
import java.util.Collections; 
import java.util.Comparator; 
import android.view.View.OnClickListener; 

public class MainNote extends AppCompatActivity { 
private ListView mListNotes; 

@Override 
protected void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 
    setContentView(R.layout.activity_main_note); 
    mListNotes = (ListView) findViewById(R.id.main_listview); 
} 

@Override 
public boolean onCreateOptionsMenu(Menu menu) { 
    getMenuInflater().inflate(R.menu.menu_main_activity, menu); 
    return true; 
} 

@Override 
public boolean onOptionsItemSelected(MenuItem item) { 
    switch (item.getItemId()) { 
        case R.id.action_create: 
            //run NoteActivity in new note mode 
            startActivity(new Intent(this, NoteActivity.class)); 
            break; 
        case R.id.action_settings: 
            //TODO show settings activity 
            break; 
    } 
    return super.onOptionsItemSelected(item); 
} 

@Override 
protected void onResume() { 
    super.onResume(); 
    //load saved notes into the listview 
    //first, reset the listview 
    mListNotes.setAdapter(null); 
    ArrayList<Note> notes = Utilities.getAllSavedNotes(getApplicationContext()); 
    //sort notes from new to old 
    Collections.sort(notes, new Comparator<Note>() { 
        @Override 
        public int compare(Note lhs, Note rhs) { 
            if (lhs.getDateTime() > rhs.getDateTime()) { 
                return -1; 
            } else { 
                return 1; 
            } 
        } 
    }); 

    if (notes != null && notes.size() > 0) { 
        //check if we have any notes! 
        final NoteAdapter na = new NoteAdapter(this, R.layout.view_note_item, notes); 
        mListNotes.setAdapter(na); 

        //set click listener for items in the list, by clicking each item the note should be loaded into NoteActivity 
        mListNotes.setOnItemClickListener(new AdapterView.OnItemClickListener() { 
            @Override 
            public void onItemClick(AdapterView<?> parent, View view, int position, long id) { 
                //run the NoteActivity in view/edit mode 
                String fileName = ((Note) mListNotes.getItemAtPosition(position)).getDateTime() + Utilities.FILE_EXTENSION; 
                Intent viewNoteIntent = new Intent(getApplicationContext(), NoteActivity.class); 
                viewNoteIntent.putExtra(Utilities.EXTRAS_NOTE_FILENAME, fileName); 
                startActivity(viewNoteIntent); 
            } 
        }); 
    } else { 
        //remind user that we have no notes! 
        Toast.makeText(getApplicationContext(), "you have no saved notes!\ncreate some new notes :)" , Toast.LENGTH_SHORT).show(); 
    } 
} 
}

activity_main_note.xml #

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" xmlns:tools="http://schemas.android.com/tools" android:layout_width="match_parent" android:layout_height="match_parent" android:paddingBottom="@dimen/activity_vertical_margin" android:paddingLeft="@dimen/activity_horizontal_margin" android:paddingRight="@dimen/activity_horizontal_margin" android:paddingTop="@dimen/activity_vertical_margin" tools:context="com.example.lenovo.home.MainNote"> 
<ListView android:id="@+id/main_listview" android:layout_width="match_parent" android:layout_height="match_parent" android:visibility="visible" /> 
</LinearLayout>

更新补充：styles.xml #

<resources> 
<!-- Base application theme. --> 
<style name="AppTheme" parent="Theme.AppCompat.Light.NoActionBar"> 
<!-- Customize your theme here. --> 
<item name="colorPrimary">@color/colorPrimary</item> 
<item name="colorPrimaryDark">@color/colorPrimaryDark</item> 
<item name="colorAccent">@color/colorAccent</item> 
</style> 
<style name="AppTheme.NoActionBar"> 
<item name="windowActionBar">false</item> 
<item name="windowNoTi

嘿，我一眼就瞅出问题所在啦！你的菜单图标不显示核心原因是当前主题没有ActionBar！

看你styles.xml里的AppTheme，父主题是Theme.AppCompat.Light.NoActionBar，而且还额外设置了windowActionBar=false——这相当于直接把承载菜单的ActionBar给关掉了，菜单图标自然没地方落脚。给你两个简单的解决办法：

方法一：切换带ActionBar的主题 #

直接修改styles.xml里的AppTheme父主题，换成带ActionBar的版本，比如Theme.AppCompat.Light.DarkActionBar，这样系统会自动给你生成ActionBar，菜单图标就能正常显示了。修改后的代码大概是这样：

<resources>
    <!-- Base application theme. -->
    <style name="AppTheme" parent="Theme.AppCompat.Light.DarkActionBar">
        <!-- Customize your theme here. -->
        <item name="colorPrimary">@color/colorPrimary</item>
        <item name="colorPrimaryDark">@color/colorPrimaryDark</item>
        <item name="colorAccent">@color/colorAccent</item>
    </style>
</resources>

方法二：手动添加Toolbar替代ActionBar #

如果你就是想用无ActionBar的主题，那可以手动在布局里加个Toolbar，然后把它设置成ActionBar来用：

1. 先修改activity_main_note.xml，添加上Toolbar：

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    tools:context="com.example.lenovo.home.MainNote">

    <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"/>

    <ListView
        android:id="@+id/main_listview"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:visibility="visible" />
</LinearLayout>

2. 再在MainNote.java的onCreate方法里添加两行代码，把Toolbar设置为ActionBar：

Toolbar toolbar = findViewById(R.id.toolbar);
setSupportActionBar(toolbar);

另外提一句，你styles.xml里的AppTheme.NoActionBar代码没写完，记得补全，但这不是当前问题的核心，先解决ActionBar的问题就行～

内容的提问来源于stack exchange，提问作者user9815533