How to change value of variable after button click and get that value in different activity

Question

I have a button. When I click the button, I want to change the value of the variable to 3. In another activity, I want to be able to get the value of the variable and do some computation based on that value.

I have tried using getters and setters methods and just traditionally changing the values and nothing seems to work.

//MainActivity.java


        mButtonChoice2 = (Button)findViewById(R.id.choice2);

        mButtonChoice2.setOnClickListener(new View.OnClickListener(){
            @Override
            public void onClick(View view){
                //My logic for Button goes in here

                if (mButtonChoice2.getText() == "Three"){
                    setDays(3);
                    openActivity();

                }

     }


   public int getDays() {

        return days;
    }

    public void setDays(int value){
        days = value;
    }

    public void openActivity() {
        Intent intent = new Intent(this, SecondActivity.class);
        startActivity(intent);
    }



//SecondActivity.java



public class SecondActivity extends AppCompatActivity {

    private TextView textview;
    private MainActivity obj = new MainActivity();

    Integer days = obj.getDays();

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

        textview = findViewById(R.id.program);

        if (days == 3) {
            textview.setText("Days is 3");
        }
        else {
            textview.setText(days);
        }

I want the textview in the SecondActivity to update the textview text with "days is 3"

However, it just errors out because it is not being able to correctly receive the value of the integer days.

Answer 1

try the following updated code:

//MainActivity.java


        mButtonChoice2 = (Button)findViewById(R.id.choice2);

        mButtonChoice2.setOnClickListener(new View.OnClickListener(){
            @Override
            public void onClick(View view){
                //My logic for Button goes in here

                if (mButtonChoice2.getText() == "Three"){
                    setDays(3);
                    openActivity();

                }

     }


   public int getDays() {

        return days;
    }

    public void setDays(int value){
        days = value;
    }

    public void openActivity() {
        Intent intent = new Intent(this, SecondActivity.class);
        intent.putExtra ("days",days);
        startActivity(intent);
    }



//SecondActivity.java



public class SecondActivity extends AppCompatActivity {

    private TextView textview;
    private MainActivity obj = new MainActivity();

   // Integer days = obj.getDays();
   int days=0;

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

       Intent intent=getIntent();days=intent.getIntExtra ("days",0);


        textview = findViewById(R.id.program);

        if (days == 3) {
            textview.setText("Days is 3");
        }
        else {
            textview.setText(days);
        }

Reference : https://developer.android.com/reference/android/content/Intent https://www.dev2qa.com/passing-data-between-activities-android-tutorial/

Answer 2

只需在一个活动中声明一个静态变量，然后在第二个活动中使用它即可。