How to pass information from one java class to another

Question

I need to pass one parameter from one Java class(A) to another Java class(B). I use many solutions from the Internet but it couldn't solve my problem. The user will choose their answer from a list of radio button. The score will be added and I need to pass the score to B class.

In B class, the user continues to answer the question and I need to add the score from both A and B class to get the final score and display it at the bottom of B class. The application keep stopped when I click on the button in A class. But I think the problem is in B class. Does anyone know how to solve this? Thank you so much.

A class

 private int score;
protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.a);


        Button btn = findViewById(R.id.anxnext);

        final RadioGroup rg1 =  findViewById(R.id.anxq1g);
        final RadioGroup rg2 =  findViewById(R.id.anxq2g);

btn.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                // Get the checked Radio Button ID from Radio Group
                int g1 = rg1.getCheckedRadioButtonId();
                int g2 = rg2.getCheckedRadioButtonId();

                if (g1 != -1) {
                    View radioButton = rg1.findViewById(g1);
                    idx1 = rg1.indexOfChild(radioButton);
                }
                if (g2 != -1) {
                    View radioButton = rg2.findViewById(g2);
                    idx2 = rg2.indexOfChild(radioButton);
                }
              score=idx1+idx2;
        Intent intent = new Intent(A.this, B.class);
                intent.putExtra("message", score);
                startActivity(intent);
            }
        });
    }

B class

 private int score1,totalscore;
 protected void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);
        setContentView(R.layout.b);

        Bundle extras = getIntent().getExtras();
        if(extras!=null) {
            String m= extras.getString("message");
            totalscore=Integer.parseInt(m);
        }
            Button btn = findViewById(R.id.anxresult);
            final TextView tv_result = findViewById(R.id.tv_result);

            final RadioGroup rg10 = findViewById(R.id.anxq10g);
            final RadioGroup rg11 = findViewById(R.id.anxq11g);

  btn.setOnClickListener(new View.OnClickListener() {
                @Override
                public void onClick(View v) {
                    // Get the checked Radio Button ID from Radio Grou[
                    int g1 = rg10.getCheckedRadioButtonId();
                    int g2 = rg11.getCheckedRadioButtonId();
                    if (g1 != -1) {
                        View radioButton = rg10.findViewById(g1);
                        idx10 = rg10.indexOfChild(radioButton);
                    }
                    if (g2 != -1) {
                        View radioButton = rg11.findViewById(g2);
                        idx11 = rg11.indexOfChild(radioButton);
                    }
                    score1 = idx10 + idx11;
                    totalscore = score1 + totalscore;
                    tv_result.setText(totalscore + " selected.");
                }
            });


    }

Below showed in the logcat

What is that app keep stopping message which is displayed in logcat? — Akshay Kumar S, Jul 10 '19 at 10:03
Hi, thanks for your reply, I have already added in the error in logcat :) — Kim E. R, Jul 10 '19 at 12:36
I don't think the error screenshot is helpful, seems like it is not pointing to the actual error — LiuWenbin_NO., Jul 10 '19 at 12:42

score 0 · Answer 1 · answered Jul 10 '19 at 10:09

try like this example

<RadioGroup
    android:id="@+id/radioSex"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content" >

    <RadioButton
        android:id="@+id/radioMale"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="@string/radio_male" 
        android:checked="true" />

    <RadioButton
        android:id="@+id/radioFemale"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="@string/radio_female" />

</RadioGroup>

In your class A

radioSexGroup = (RadioGroup) findViewById(R.id.radioSex);
btnDisplay = (Button) findViewById(R.id.btnDisplay);

btnDisplay.setOnClickListener(new OnClickListener() {

    @Override
    public void onClick(View v) {

            // get selected radio button from radioGroup
        int selectedId = radioSexGroup.getCheckedRadioButtonId();

        // find the radiobutton by returned id
            radioSexButton = (RadioButton) findViewById(selectedId);

        Toast.makeText(MyAndroidAppActivity.this,
            radioSexButton.getText(), Toast.LENGTH_SHORT).show();

    }

});

post the crash report to know more about your issue

score 0 · Accepted Answer · answered Jul 10 '19 at 12:51

Take care of the data type:

In A class, you have:

score=idx1+idx2;
        Intent intent = new Intent(A.this, B.class);
                intent.putExtra("message", score);
                startActivity(intent);

which score is int, however in B class:

Bundle extras = getIntent().getExtras();
        if(extras!=null) {
            String m= extras.getString("message");
            totalscore=Integer.parseInt(m);
        }

You are trying to get it as a String, and it is null so the app crashes.

So please change it to:

Bundle extras = getIntent().getExtras();
        if(extras!=null) {
            totalscore = extras.getInt("message");
        }

And try again

Thank you so much, it helps :) – Kim E. R Jul 10 '19 at 13:00 — Kim E. R, Jul 10 '19 at 13:00

How to pass information from one java class to another

2 Answers2