Developing your first android app — Simple calculator

Hello everyone, welcome to Android Hunger. Here I am going to tell you ‘How to create your first android app !’

This is a simple app which takes two numbers and perform arithmetic operations like addition, subtraction, multiplication, and division on them.

First Android App — androidhunger.com

• Here I made two simple EditText with a TextView for each of them.
• 4 Buttons for each operation (addition, subtraction, multiplication and division)
• A TextView for displaying a result.

In the previous post, I discussed on different UI layouts in android, here I used LinearLayout for designing the above screen, also nested some LinearLayouts with horizontal and vertical orientation for achieving it.

Below is the component tree of the view,

First Android App — androidhunger.com

First, we design the layout of the app, here we use XML to do it,

The code for `activity_main.xml`,

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:gravity="center"
    android:orientation="vertical"
    tools:context="simplecalculator.avinashnethala.com.simplecalculator.MainActivity">
<LinearLayout
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:orientation="horizontal">
<TextView
            android:id="@+id/textView"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="@string/fNum"
            android:textAppearance="?android:attr/textAppearanceMedium" />
<EditText
            android:id="@+id/firstNum"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:ems="10"
            android:inputType="numberDecimal" />
    </LinearLayout>
<LinearLayout
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:orientation="horizontal">
<TextView
            android:id="@+id/textViews"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="@string/sNum"
            android:textAppearance="?android:attr/textAppearanceMedium" />
<EditText
            android:id="@+id/secondNum"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:ems="10"
            android:inputType="numberDecimal" />
    </LinearLayout>
<View
        android:layout_width="0dp"
        android:layout_height="25dp" />
<LinearLayout
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="center"
        android:orientation="vertical">
<LinearLayout
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:orientation="horizontal"
            android:padding="5dp">
<Button
                android:id="@+id/add"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:background="#9fa8da"
                android:text="+"
android:textColor="@color/colorAccent"
                android:textSize="50sp" />
<View
                android:layout_width="5dp"
                android:layout_height="0dp" />
<Button
                android:id="@+id/sub"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:background="#9fa8da"
                android:text="-"
android:textColor="@color/colorAccent"
                android:textSize="50sp" />
        </LinearLayout>
<LinearLayout
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:orientation="horizontal"
            android:padding="5dp">
<Button
                android:id="@+id/mul"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:background="#9fa8da"
                android:text="*"
                android:textColor="@color/colorAccent"
                android:textSize="50sp" />
<View
                android:layout_width="5dp"
                android:layout_height="0dp" />
<Button
                android:id="@+id/div"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:background="#9fa8da"
                android:text="/"
                android:textColor="@color/colorAccent"
                android:textSize="50sp" />
        </LinearLayout>
    </LinearLayout>
<View
        android:layout_width="0dp"
        android:layout_height="25dp" />
<TextView
        android:id="@+id/res"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="center"
        android:textSize="35sp" />
</LinearLayout>

The functionality part is generally written in java,

In the `MainActivity` I initialize the widgets used like Button, TextViews, and EditTexts.

final EditText first = (EditText) findViewById(R.id.firstNum);
final EditText second = (EditText) findViewById(R.id.secondNum);
final TextView res = (TextView) findViewById(R.id.res);
Button sum = (Button) findViewById(R.id.add);
Button sub = (Button) findViewById(R.id.sub);
Button mul = (Button) findViewById(R.id.mul);
Button div = (Button) findViewById(R.id.div);

Now when these buttons are clicked a specific operation is performed, so I set OnClickListener to them.

sum.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Double fNum = Double.valueOf(first.getText().toString());
                Double sNum = Double.valueOf(second.getText().toString());
                res.setText(String.valueOf(fNum + sNum));
            }
        });

Above code is for addition operation, similarly, we perform for all other three operations(subtraction, multiplication, and division).

First Android App — androidhunger.com

Post : http://androidhunger.com/your-first-android-app-simple-calculator/

Developing your first android app - Simple calculator

Github : https://github.com/avinashn/android_simple_calculator

GitHub - avinashn/android_simple_calculator: This is a basic app which takes 2 numbers and perform…