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Basic Calculator Android Studio
sumanthdosapati edited this page Aug 17, 2018
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1 revision
Create a new Android application project with an application name: “Calculator” and package name: “com.sumanth.calculator”.
By default Android uses a green Android robot icon. In this project, we are going to use a custom application icon. Therefore, delete the default ic_launcher icon set from the “mipmap” folder.
Get any PNG image file for the application icon. (It is recommended to have a minimum size 256x256 pixels). This icon is used to display in the Google Play as well as in the applications menu of Android devices.
Right click on the “mipmap” folder and select New → Image Asset
Browse and select your icon as the image file and click on Next → Finish buttons. (Make sure that the resource name is: ic_launcher)
Replace the content of activity_main.xml file by the following code. This code creates a TextView as the calculator number screen and some necessary buttons. TextView is used instead of EditText, in order to prevent manual user input using the default keypad of Android. In this code, some common properties of Buttons are not provided to reduce the length of this tutorial. In your code make sure that you have included these four attributes for all the Buttons.
android:layout_width="0dp"
android:layout_height="match_parent"
android:layout_weight="1"
android:textSize="30sp"
<RelativeLayout 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"
tools:context=".MainActivity">
````<TextView````
````android:id="@+id/txtScreen"````
````android:layout_width="match_parent"````
````android:layout_height="wrap_content"````
````android:layout_alignParentTop="true"````
````android:layout_centerHorizontal="true"````
````android:gravity="right|center_vertical"````
````android:maxLength="16"````
````android:padding="10dp"````
````android:textAppearance="?android:attr/textAppearanceLarge"````
````android:textSize="30sp"````
````android:typeface="serif" />````
````<LinearLayout````
````android:layout_width="match_parent"````
````android:layout_height="match_parent"````
````android:layout_below="@+id/txtScreen"````
````android:orientation="vertical">````
````<LinearLayout````
````android:layout_width="match_parent"````
````android:layout_height="0dp"````
````android:layout_weight="1">````
````<Button````
````android:id="@+id/btnSeven"````
````android:text="7" />````
````<Button````
````android:id="@+id/btnEight"````
````android:text="8" />````
````<Button````
````android:id="@+id/btnNine"````
````android:text="9"/>````
````<Button````
````android:id="@+id/btnDivide"````
````android:text="/"/>````
````</LinearLayout>````
````<LinearLayout````
````android:layout_width="match_parent"````
````android:layout_height="0dp"````
````android:layout_weight="1">````
````<Button````
````android:id="@+id/btnFour"````
````android:text="4"/>````
````<Button````
````android:id="@+id/btnFive"````
````android:text="5" />````
````<Button````
````android:id="@+id/btnSix"````
````android:text="6" />````
````<Button````
````android:id="@+id/btnMultiply"````
````android:text="*" />````
````</LinearLayout>````
````<LinearLayout````
````android:layout_width="match_parent"````
````android:layout_height="0dp"````
````android:layout_weight="1">````
````<Button````
````android:id="@+id/btnOne"````
````android:text="1" />````
````<Button````
````android:id="@+id/btnTwo"````
````android:text="2" />````
````<Button````
````android:id="@+id/btnThree"````
````android:text="3" />````
````<Button````
````android:id="@+id/btnSubtract"````
````android:text="-" />````
````</LinearLayout>````
````<LinearLayout````
````android:layout_width="match_parent"````
````android:layout_height="0dp"````
````android:layout_weight="1">````
````<Button````
````android:id="@+id/btnDot"````
````android:text="." />````
````<Button````
````android:id="@+id/btnZero"````
````android:text="0" />````
````<Button````
````android:id="@+id/btnClear"````
````android:text="C" />````
````<Button````
````android:id="@+id/btnAdd"````
````android:text="+" />````
````</LinearLayout>````
````<Button````
````android:id="@+id/btnEqual"````
````android:text="=" />````
````</LinearLayout>````
</RelativeLayout>
### Step 7:
Right click on the “drawable” folder and select New → Drawable resource file.
### Step 8:
Create a drawable file with a name button.
### Step 9:
Replace the content of button.xml by the following code. This drawable resource is used to decorate the buttons of the calculator. There are two gradient shapes in this code; one is for button pressed state and another for normal state.
<?xml version="1.0" encoding="utf-8" ?>
<selector xmlns:android="http://schemas.android.com/apk/res/android">
<item android:state_pressed="true">
<shape>
<gradient android:angle="90" android:endColor="#FFFFFF" android:startColor="#9EB8FF" android:type="linear" />
<padding android:bottom="0dp" android:left="0dp" android:right="0dp" android:top="0dp" />
<size android:width="60dp" android:height="60dp" />
<stroke android:width="1dp" android:color="#ff3da6ef" />
</shape>
</item>
<item>
<shape>
<gradient android:angle="90" android:endColor="#FFFFFF" android:startColor="#ffd9d9d9" android:type="linear" />
<padding android:bottom="0dp" android:left="0dp" android:right="0dp" android:top="0dp" />
<size android:width="60dp" android:height="60dp" />
<stroke android:width="0.5dp" android:color="#ffcecece" />
</shape>
</item>
</selector>
### Step 10:
For all the buttons in the activity_main.xml, add a property “android:background”.
android:background="@drawable/button"
After the modification, activity_main.xml must be like this.
### Step 11:
To evaluate the arithmetic expressions, exp4J library is used in this project. Open the “build.gradle (Module: app)” file from the Gradle scripts. Add a dependency 'net.objecthunter:exp4j:0.4.4' to the project as shown below.
dependencies {
compile fileTree(dir: 'libs', include: ['*.jar'])
compile 'com.android.support:appcompat-v7:21.0.3'
compile 'net.objecthunter:exp4j:0.4.4'
}
Once you save the file, Android Studio will ask to sync the project. Allow it to sync by clicking on the link appeared on top left corner. (You need an active Internet connection to download the libraries by Gradle)
### Step 12:
Modify the MainActivity.java as provided below. Complete description about the code is provided in comments.
package com.sumanth.calculator;
import android.os.Bundle;
import android.support.v7.app.ActionBarActivity;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;
import net.objecthunter.exp4j.Expression;
import net.objecthunter.exp4j.ExpressionBuilder;
public class MainActivity extends ActionBarActivity {
// IDs of all the numeric buttons
private int[] numericButtons = {R.id.btnZero, R.id.btnOne, R.id.btnTwo, R.id.btnThree, R.id.btnFour, R.id.btnFive, R.id.btnSix, R.id.btnSeven, R.id.btnEight, R.id.btnNine};
// IDs of all the operator buttons
private int[] operatorButtons = {R.id.btnAdd, R.id.btnSubtract, R.id.btnMultiply, R.id.btnDivide};
// TextView used to display the output
private TextView txtScreen;
// Represent whether the lastly pressed key is numeric or not
private boolean lastNumeric;
// Represent that current state is in error or not
private boolean stateError;
// If true, do not allow to add another DOT
private boolean lastDot;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
// Find the TextView
this.txtScreen = (TextView) findViewById(R.id.txtScreen);
// Find and set OnClickListener to numeric buttons
setNumericOnClickListener();
// Find and set OnClickListener to operator buttons, equal button and decimal point button
setOperatorOnClickListener();
}
/**
* Find and set OnClickListener to numeric buttons.
*/
private void setNumericOnClickListener() {
// Create a common OnClickListener
View.OnClickListener listener = new View.OnClickListener() {
@Override
public void onClick(View v) {
// Just append/set the text of clicked button
Button button = (Button) v;
if (stateError) {
// If current state is Error, replace the error message
txtScreen.setText(button.getText());
stateError = false;
} else {
// If not, already there is a valid expression so append to it
txtScreen.append(button.getText());
}
// Set the flag
lastNumeric = true;
}
};
// Assign the listener to all the numeric buttons
for (int id : numericButtons) {
findViewById(id).setOnClickListener(listener);
}
}
/**
* Find and set OnClickListener to operator buttons, equal button and decimal point button.
*/
private void setOperatorOnClickListener() {
// Create a common OnClickListener for operators
View.OnClickListener listener = new View.OnClickListener() {
@Override
public void onClick(View v) {
// If the current state is Error do not append the operator
// If the last input is number only, append the operator
if (lastNumeric && !stateError) {
Button button = (Button) v;
txtScreen.append(button.getText());
lastNumeric = false;
lastDot = false; // Reset the DOT flag
}
}
};
// Assign the listener to all the operator buttons
for (int id : operatorButtons) {
findViewById(id).setOnClickListener(listener);
}
// Decimal point
findViewById(R.id.btnDot).setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
if (lastNumeric && !stateError && !lastDot) {
txtScreen.append(".");
lastNumeric = false;
lastDot = true;
}
}
});
// Clear button
findViewById(R.id.btnClear).setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
txtScreen.setText(""); // Clear the screen
// Reset all the states and flags
lastNumeric = false;
stateError = false;
lastDot = false;
}
});
// Equal button
findViewById(R.id.btnEqual).setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
onEqual();
}
});
}
/**
* Logic to calculate the solution.
*/
private void onEqual() {
// If the current state is error, nothing to do.
// If the last input is a number only, solution can be found.
if (lastNumeric && !stateError) {
// Read the expression
String txt = txtScreen.getText().toString();
// Create an Expression (A class from exp4j library)
Expression expression = new ExpressionBuilder(txt).build();
try {
// Calculate the result and display
double result = expression.evaluate();
txtScreen.setText(Double.toString(result));
lastDot = true; // Result contains a dot
} catch (ArithmeticException ex) {
// Display an error message
txtScreen.setText("Error");
stateError = true;
lastNumeric = false;
}
}
}
}
### Step 13:
Save all the changes and run the application.
Note:This is just to provide a basic knowledge of Android and doesn't mean for any repositry