[Android / Java] Creating a super-simple Option Menu (API not implemented)

Introduction

I'm a super beginner with 1 week of Android development history. I created a simple OptionMenu as an output. It took a long time just to implement this, so I hope it will be helpful for the same beginners.

• The strings file is not used to omit the description amount.

App overview

A super-simple app that changes the displayed message when you press the save button installed at the top right of the screen 　

Code for each file

Display layout setting of option menu

1. Create an xml file for the option menu in the res / menu folder.
2. Create the outline of the option menu with the menu tag, and the menu elements (save button) with the item tag.
3. Three attributes required for item tag android: id: Key for linking menu file and java file android: title: Character string to be displayed in the menu app: showAsAction: Whether to show in the action bar (never <ifRoom <always)

option_menu.xml

//Delete all the first default sentences and write the following
<?xml version="1.0" encoding="utf-8"?>
<menu xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:android="http://schemas.android.com/apk/res/android">
    
    <item android:id="@+id/option_save"
        android:title="Save"
        app:showAsAction="always" />

</menu>

Main screen layout settings

android: id: Key for linking layout file and java file android: text: Character string to be displayed on the main screen

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"
    tools:context=".MainActivity">

　　 //Just mess with id and text
    <TextView
        android:id="@+id/text_view"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Let's press the save button"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

</androidx.constraintlayout.widget.ConstraintLayout>

java file

• Package and import statements are omitted. (Press option + Enter when it turns red)

Think of the following two methods as rules for implementing option menus. onCreateOptionsMenu(Menu menu) onOptionsItemSelected(MenuItem item)

MainActivity.java

public class MainActivity extends AppCompatActivity {
    //Leave the default ok
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
    }

    //Display of option menu (save button)
    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // MenuInflater(A class for inflating menus to Java objects)Get
        MenuInflater inflater = getMenuInflater();
        // option_menu.Inflate the menu part described in xml into a Java object
        inflater .inflate(R.menu.option_menu, menu);
        //Return the return value
        return true;
    }

    //Processing when the option menu (save button) is selected
    @Override
    public boolean onOptionsItemSelected(MenuItem item)
        // activity_main.Get TextView of xml
        TextView textView = findViewById(R.id.text_view);
        //Set a new character string in the acquired text
        textView.setText("The save button was pressed");
        //Return the return value
        return true;
    }
}

Finally

Since I am a super beginner, please point out any differences.

Reference site

・ Https://developer.android.com/guide/topics/ui/menus?hl=ja#options-menu ・ Https://qiita.com/watataku/items/5faad0384b54d0c53f6e Thank you very much!