Simple Calculator app keeps crashes

Question

I'm a beginner in Android. Just started working on a Calculator app and don't know why the app keeps crashing all the time.

I have Two Activities... MainActivity and CalculatorActivity

MainActivity:

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

                calcubtn = (Button) findViewById(R.id.calculatorbtn);
                calcubtn.setOnClickListener(new View.OnClickListener() 
                {
                    @Override
                    public void onClick(View view) 
                    {
                        Intent calculator = new Intent(MainActivity.this, CalculatorActivity.class);
                        startActivity(calculator);
                    }
                });
            }   
      }

MainActivity Layout:

<?xml version="1.0" encoding="utf-8"?>
    <RelativeLayout 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="com.example.rfkha.myfirstapp.MainActivity">


        <TextView
            android:id="@+id/textView"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_alignParentTop="true"
            android:layout_centerHorizontal="true"
            android:layout_marginTop="13dp"
            android:textSize="27sp"
            android:textColor="@android:color/holo_red_light"
            android:text="@string/functions_text" />

        <Button
            android:id="@+id/calculatorbtn"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_alignParentStart="true"
            android:layout_below="@+id/textView"
            android:layout_marginStart="43dp"
            android:layout_marginTop="70dp"
            android:text="@string/calcu_string"

            />

    </RelativeLayout>

CalculatorActivity: (i.e child activity)

Here in the activity class, I've added implements View.OnclickListener . I found it in stackoverflow somewhere. I think the problem is from this thing. Also it required to used the keyword abstractto use it with the activity class, so i used that too.

public abstract class CalculatorActivity extends AppCompatActivity implements View.OnClickListener {

        Button btn1, btn2, btn3, btn4, btn5, btn6, btn7, btn8, btn9, zerobtn, dotbtn, equalbtn, minusbtn, sumbtn, divbtn, mulbtn;
        double num1, num2;
        boolean sum, minus, div, mul;
        EditText textarea= (EditText) findViewById(R.id.textarea);

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

            btn1 = (Button) findViewById(R.id.btn1);
            btn1.setOnClickListener(this);
            (((Same Code for buttons upto 9 and SUM, MINUS, DIVISION and MULtiplication Buttons)))

            }

        @Override
        public void onClick(View v)
        {
            switch (v.getId())
            {
                case R.id.btn1: {
                    textarea.setText(textarea.getText()+"1");
                    break;
                }
                case R.id.btn2: {
                    textarea.setText(textarea.getText()+"2");
                    break;
                }
                case R.id.btn3:

               (((((  And So on... Upto Button 9  ))))))


                case R.id.zerobtn: {
                    textarea.setText(textarea.getText()+"0");
                    break;
                }
                case R.id.dotbtn: {
                    textarea.setText(textarea.getText()+".");
                    break;
                }
                case R.id.sumbtn: {
                    num1=Double.parseDouble(textarea.getText().toString());
                    sum=true;
                    textarea.setText(null);
                    break;
                }
                   (((((Likewise for Minus, Division and Multiplication buttons))))))))))

                case R.id.equalbtn:
                    {
                        if (num1!=0)
                        {
                            num2=Double.parseDouble(textarea.getText().toString());
                            if (sum) {
                                textarea.setText(num1+num2+"");
                                sum=false;
                            }
                            else if(mul) {
                                textarea.setText(num1*num2+"");
                                mul=false;
                            }
                            else if(div) {
                                textarea.setText(num1/num2+"");
                                div=false;
                            }
                            else if(minus) {
                                textarea.setText(num1-num2+"");
                                minus=false;
                            }

                        }
                        else{
                             Toast.makeText(getApplicationContext(), "First select a number!!", Toast.LENGTH_SHORT);
                        }
                    break;
                    }        
            }
        }
    }

Calculator Activity Layout:

<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"
        android:orientation="vertical"
        android:weightSum="1"
        tools:context="com.example.rfkha.myfirstapp.CalculatorActivity">

        <TextView
            android:id="@+id/textView2"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:layout_marginBottom="13dp"
            android:layout_marginTop="8dp"
            android:gravity="center_horizontal"
            android:text="@string/calculatortxt"
            android:textSize="25sp" />

        <EditText
            android:id="@+id/textarea"
            android:layout_width="351dp"
            android:layout_height="154dp"
            android:layout_marginStart="16dp"
            android:ems="10"
            android:hint="@string/resultsString"
            android:textSize="33sp"
            android:textAlignment="textEnd"
            android:padding="11dp"
            android:inputType="textPersonName" />

        <LinearLayout
            android:layout_width="match_parent"
            android:layout_height="50dp"
            android:gravity="center_horizontal"
            android:orientation="horizontal"
            android:weightSum="1">

            <Button
                android:id="@+id/clearbt"
                android:layout_width="293dp"
                android:layout_height="51dp"
                android:text="@string/cetxt"
                android:textSize="24sp" />

        </LinearLayout>

        <LinearLayout
            android:layout_width="match_parent"
            android:layout_height="50dp"
            android:gravity="center_horizontal"
            android:orientation="horizontal">

            <Button
                android:id="@+id/btn7"
                android:layout_width="68dp"
                android:layout_height="51dp"
                android:text="7"
                android:textSize="24sp" />

            <Button
                android:id="@+id/btn8"
                android:layout_width="68dp"
                android:layout_height="51dp"
                android:text="8"
                android:textSize="24sp" />

            <Button
                android:id="@+id/btn9"
                android:layout_width="68dp"
                android:layout_height="51dp"
                android:text="9"
                android:textSize="24sp" />

            <Button
                android:id="@+id/mulbtn"
                android:layout_width="68dp"
                android:layout_height="51dp"
                android:layout_marginStart="27dp"
                android:text="x"
                android:textSize="18sp" />
        </LinearLayout>

        <LinearLayout
            android:layout_width="match_parent"
            android:layout_height="50dp"
            android:gravity="center_horizontal"
            android:orientation="horizontal">

            <Button
                android:id="@+id/btn4"
                android:layout_width="68dp"
                android:layout_height="51dp"
                android:text="4"
                android:textSize="24sp" />

            <Button
                android:id="@+id/btn5"
                android:layout_width="68dp"
                android:layout_height="51dp"
                android:text="5"
                android:textSize="24sp" />

            <Button
                android:id="@+id/btn6"
                android:layout_width="68dp"
                android:layout_height="51dp"
                android:text="6"
                android:textSize="24sp" />

            <Button
                android:id="@+id/minusbtn"
                android:layout_width="68dp"
                android:layout_height="51dp"
                android:layout_marginStart="27dp"
                android:text="-"
                android:textSize="24sp" />
        </LinearLayout>

        <LinearLayout
            android:layout_width="match_parent"
            android:layout_height="50dp"
            android:gravity="center_horizontal"
            android:orientation="horizontal">

            <Button
                android:id="@+id/btn1"
                android:layout_width="68dp"
                android:layout_height="51dp"
                android:text="1"
                android:textSize="24sp" />

            <Button
                android:id="@+id/btn2"
                android:layout_width="68dp"
                android:layout_height="51dp"
                android:text="2"
                android:textSize="24sp" />

            <Button
                android:id="@+id/btn3"
                android:layout_width="68dp"
                android:layout_height="51dp"
                android:text="3"
                android:textSize="24sp" />

            <Button
                android:id="@+id/sumbtn"
                android:layout_width="68dp"
                android:layout_height="51dp"
                android:layout_marginStart="27dp"
                android:text="+"
                android:textSize="24sp" />
        </LinearLayout>

        <LinearLayout
            android:layout_width="match_parent"
            android:layout_height="50dp"
            android:gravity="center_horizontal"
            android:orientation="horizontal">

            <Button
                android:id="@+id/dotbtn"
                android:layout_width="68dp"
                android:layout_height="51dp"
                android:text="."
                android:textSize="24sp" />

            <Button
                android:id="@+id/zerobtn"
                android:layout_width="68dp"
                android:layout_height="51dp"
                android:text="0"
                android:textSize="24sp" />

            <Button
                android:id="@+id/equalbtn"
                android:layout_width="68dp"
                android:layout_height="51dp"
                android:text="="
                android:textSize="24sp" />

            <Button
                android:id="@+id/divbtn"
                android:layout_width="68dp"
                android:layout_height="51dp"
                android:layout_marginStart="27dp"
                android:text="/"
                android:textSize="24sp" />
        </LinearLayout>


    </LinearLayout>

Logcat: (Errors)

Link to Logcat: https://pastebin.com/hbwZVUZg

Exactly what error do you get when it crashes? If you're giving us this much code, also give us something to *pinpoint* where the error is. — hnefatl, Sep 08 '17 at 19:30
What's the error on your LogCat? did you setup your activity on the manifest? [check here][1] [1]: https://stackoverflow.com/questions/20870202/how-to-add-activity-to-manifest-xml-in-right-way — Xaren, Sep 08 '17 at 19:32
@hnefatl Check the "CalculatorActivity" where I've mentioned the error. By the way the error is not shown in android studio but still the app crashes — Arif Khan, Sep 08 '17 at 19:34
@ArifKhan It's highly unlikely that there isn't an error in LogCat — peterulb, Sep 08 '17 at 19:37

Xaren · Accepted Answer · 2017-09-08T19:54:28.013

Delete the abstract keyword. then the line textarea= (EditText) findViewById(R.id.textarea); change for EditText textarea; and last put this on the onCreate() textarea = (EditText)findViewById(R.id.textarea);

Remember that you cannot instantiate an abstract class. here

And check how to debug here

public  class CalculatorActivity extends AppCompatActivity implements View.OnClickListener {

Button btn1, btn2, btn3, btn4, btn5, btn6, btn7, btn8, btn9, zerobtn, dotbtn, equalbtn, minusbtn, sumbtn, divbtn, mulbtn;
double num1, num2;
boolean sum, minus, div, mul;
EditText textarea;

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

    textarea = (EditText) findViewById(R.id.textarea);

score 0 · Answer 2 · edited Sep 08 '17 at 19:42

0

Put this code in onCreate:

@Override
protected void onCreate(Bundle savedInstanceState) 
{
    ...
    textarea = (EditText)findViewById(R.id.textarea);
    ...
}

edited Sep 08 '17 at 19:42

hnefatl

5,860
2
27
49

answered Sep 08 '17 at 19:38

akshay_shahane

4,423
2
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30

1

Explaining why this should work would be an improvement - presumably that getting a control by ID isn't a valid operation until the activity's been created. – hnefatl Sep 08 '17 at 19:43

score 0 · Answer 3 · answered Sep 08 '17 at 21:58

0

Check whether you are using dependencies of same version or not. There should not be any version conflict among dependencies.

answered Sep 08 '17 at 21:58

amol

1
1

Problem solved bro.. it was due to the 'abstract' ... thanks to @Xaren in the 2nd comment – Arif Khan Sep 09 '17 at 05:35

Simple Calculator app keeps crashes

3 Answers3