java - 菜单项未显示在工具栏 SDK 29 中

Question

我遇到的问题是菜单按钮未显示在工具栏中。我设置了一个按钮始终显示，另一个按钮仅在有房间时显示。没有显示。

这是使用 Android SDK 29 (Q) 编译的。

(我在 Stack Overflow 上搜索过类似的问题，但其他问题至少是几年前写的，并且使用的是较旧的 SDK。)

activity_main.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"
    android:background="@color/tealBlue"
    tools:context=".view.MainActivity">

    <androidx.appcompat.widget.Toolbar
        app:layout_constraintTop_toTopOf="parent"
        android:id="@+id/toolbar_top_main"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:background="?attr/colorPrimary"
        android:minHeight="?attr/actionBarSize"
        android:theme="?attr/actionBarTheme"
        tools:menu="@menu/top_menu_overflow"
        />

    <ExpandableListView
        android:id="@+id/expandableListViewPolls"
        android:layout_width="match_parent"
        android:layout_height="0dp"
        android:layout_marginTop="8dp"
        android:layout_marginBottom="8dp"
        android:indicatorLeft="? 
   android:attr/expandableListPreferredItemIndicatorLeft"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/toolbar_top_main"

        tools:layout_editor_absoluteX="16dp" />
    ...

top_menu_overflow.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"
  >
<item android:id="@+id/action_start_voting"
    android:title="@string/start_voting_text"
    app:showAsAction="always"/>
<item android:id="@+id/action_see_voting_results"
    android:title="@string/see_voting_results_text"
    app:showAsAction="ifRoom"/>
</menu>

MainActivity.java

   import androidx.appcompat.widget.Toolbar;
        @Override
        protected void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
            setContentView(R.layout.activity_main);

            // setup toolbar
            Toolbar myToolbar = findViewById(R.id.toolbar_top_main);
            setSupportActionBar(myToolbar);
        }

样式.xml

   <resources>
           <style name="AppTheme" parent="Theme.AppCompat.Light.NoActionBar">
        ...

AndroidManifest.xml

  <?xml version="1.0" encoding="utf-8"?>
    <manifest xmlns:android="http://schemas.android.com/apk/res/android"
        xmlns:tools="http://schemas.android.com/tools"
        package="com.example.votetodo">

        <application
            android:allowBackup="false"
            android:icon="@mipmap/ic_launcher"
            android:label="@string/app_name"
            android:roundIcon="@mipmap/ic_launcher_round"
            android:supportsRtl="true"
            android:theme="@style/AppTheme"
        ...

构建.gradle

apply plugin: 'com.android.application'

    android {
    compileSdkVersion 29
    buildToolsVersion "29.0.1"
    defaultConfig {
        applicationId "com.example.votetodo"
        minSdkVersion 15
        targetSdkVersion 29
        versionCode 1
        versionName "1.0"
        testInstrumentationRunner "androidx.test.runner.AndroidJUnitRunner"
        vectorDrawables.useSupportLibrary = true


        javaCompileOptions {
            annotationProcessorOptions {
                arguments = ["room.schemaLocation": 
    "$projectDir/schemas".toString()]
            }
        }

    }
    buildTypes {
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android-optimize.txt'), 'proguard-rules.pro'
        }
    }

    dataBinding {
        enabled = true
    }
    }

    dependencies {
    implementation fileTree(dir: 'libs', include: ['*.jar'])
    implementation 'androidx.appcompat:appcompat:1.0.2'
    implementation 'androidx.constraintlayout:constraintlayout:1.1.3'
    testImplementation 'junit:junit:4.12'
    androidTestImplementation 'androidx.test:runner:1.2.0'
    androidTestImplementation 'androidx.test.espresso:espresso-core:3.2.0'


    implementation 'com.google.android.material:material:1.0.0'

    // room
    def room_version = "2.2.0-alpha01"  
    implementation "androidx.room:room-rxjava2:$room_version"
    annotationProcessor "androidx.room:room-compiler:$room_version"


    // rxandroid
    implementation "io.reactivex.rxjava2:rxandroid:2.0.1"

    }

Answer 1

发现问题了。我需要在 MainActivity.java 中添加以下方法才能膨胀菜单项。

@Override public boolean onCreateOptionsMenu(Menu menu) {
    MenuInflater inflater = getMenuInflater();
    inflater.inflate(R.menu.top_menu_overflow, menu);
    return true; 
}