AS中級 値の受け渡し編①解説～Activityから別のActivityへ値を渡す～

Try1の解答例

MainActivity.java

package com.example.gettakea2a;

import androidx.appcompat.app.AppCompatActivity;

import android.content.Intent;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;

public class MainActivity extends AppCompatActivity {
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);


        EditText xEdit = findViewById(R.id.xEdit);
        EditText yEdit = findViewById(R.id.yEdit);
        TextView frontNumber = findViewById(R.id.frontNumber);
        TextView backNumber = findViewById(R.id.backNumber);
        Button inputNextBtn = findViewById(R.id.inputNextBtn);


        inputNextBtn.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                int x = Integer.parseInt(xEdit.getText().toString());
                int y = Integer.parseInt(yEdit.getText().toString());
                int result = x + y;
                Intent intent = new Intent(MainActivity.this,SecondActivity.class);
                intent.putExtra("result",result);      ・・・・・・・・・①
                startActivity(intent);
            }
        });
    }
}

activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout 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"
    android:orientation="vertical"
    android:gravity="center_horizontal">


    <TextView
        android:id="@+id/frontNumber"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="x"/>
    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="+"/>
    <TextView
        android:id="@+id/backNumber"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="y"/>
    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="= ?"/>

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="xに代入する値"
        android:layout_margin="40sp"/>
    <EditText
        android:id="@+id/xEdit"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text=""/>
    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="yに代入する値"
        android:layout_margin="40sp"/>
    <EditText
        android:id="@+id/yEdit"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text=""/>
    <Button
        android:id="@+id/inputNextBtn"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="結果は次ページ"/>

</LinearLayout>

SecondActivity.java

package com.example.gettakea2a;

import androidx.appcompat.app.AppCompatActivity;

import android.content.Intent;
import android.os.Bundle;
import android.widget.TextView;

public class SecondActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_second);

        TextView resultNumber = findViewById(R.id.resultNumber);

        Intent intent = getIntent();
        int resultNum = intent.getIntExtra("result",0);　　　　・・・・・・②
        resultNumber.setText(String.valueOf(resultNum));
    }
}

activity_second.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout 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=".SecondActivity"
    android:gravity="center_horizontal"
    android:orientation="vertical">

    <TextView
        android:id="@+id/resultNumber"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginTop="200sp"
        android:textSize="30sp"/>

</LinearLayout>

Try2の解答例

MainActivity.java

package com.example.a2a;

import androidx.appcompat.app.AppCompatActivity;

import android.content.Intent;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;

public class MainActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        EditText frontEdit = findViewById(R.id.frontEdit);
        EditText backEdit = findViewById(R.id.backEdit);
        StringBuilder stringBuilder = new StringBuilder();

        Button fusionNextBtn = findViewById(R.id.fusionNextBtn);
        fusionNextBtn.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {

                stringBuilder.append(frontEdit.getText().toString())
                             .append(backEdit.getText().toString());
                String resultStr = stringBuilder.toString();
                //Log.v("MY_LOG",resultStr);
                Intent intent = new Intent(MainActivity.this,SecondActivity.class);
                intent.putExtra("resultStr",resultStr);
                startActivity(intent);
            }
        });
    }
}

activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout 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"
    android:gravity="center_horizontal"
    android:orientation="vertical">

    <EditText
        android:id="@+id/frontEdit"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginTop="40sp"/>
    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="+"
        android:textSize="30sp"/>
    <EditText
        android:id="@+id/backEdit"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"/>
    <Button
        android:id="@+id/fusionNextBtn"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="合体して次ページへ"/>


</LinearLayout>

SecondActivity.java

package com.example.a2a;

import androidx.appcompat.app.AppCompatActivity;

import android.content.Intent;
import android.os.Bundle;
import android.widget.TextView;

public class SecondActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_second);

        TextView resultView = findViewById(R.id.resultView);

        Intent intent = getIntent();
        String resultString = intent.getStringExtra("resultStr");
        resultView.setText(resultString);
    }
}

activity_second.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout 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=".SecondActivity"
    android:gravity="center_horizontal"
    android:orientation="vertical">

    <TextView
        android:id="@+id/resultView"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:textSize="40sp"
        android:layout_marginTop="80sp"/>

</LinearLayout>