Android Calculator

Prerequisite: Android ADT Plugin for Eclipse.

What we gonna have at the end is a calculator for Android. It will be able to summate, subtract, multiply and divide:
You need to write a number in the upper field and click a button for the operation you want. The result will be shown below the buttons.

Create your Android Project. In this case I named it Calculator and used the package de.duckout.calculator and choosed Android 2.3.3 as Build SDK and also Android 2.3.3 as Minimum Required SDK.

Strings:

As we use several strings, we start to create these.
In the Package Explorer go to “Calculator” -> “res” -> “values” -> “strings.xml”.
Choose the Graphical View. (You can always use the Graphical Interface and/or the XML View)
Press “Add” on the right side and create the following strings as shown in the next picture.

Check the the xml view, which should look like this:

<resources>

    <string name="app_name">Calculator</string>
    <string name="menu_settings">Settings</string>
    <string name="title_activity_main">Duckout Calculator</string>
    <string name="plus">+</string>
    <string name="minus">-</string>
    <string name="multiply">*</string>
    <string name="divide">/</string>
	
</resources>

Layout

Navigate in the Package Explorer to “Calculator” -> “res” -> “layout” -> “activity_main.xml”.

You can choose between Graphical Layout and a XML View. As you see I used the Graphical Layout. To add a new object, just drag & drop it from the left side (“palette”) into the middle. But I recommend you to use the XML view, you can just copy the xml code below.

I added these objects:

Check the the xml view, which should look like this:

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/Layout"
    android:layout_width="match_parent"
    android:layout_height="match_parent" >

    <EditText
        android:id="@+id/number"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignParentLeft="true"
        android:layout_alignParentTop="true"
        android:ems="10"
        android:inputType="numberDecimal" >

        <requestFocus />
    </EditText>
	
    <TableRow
        android:id="@+id/tableRow1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignParentLeft="true"
        android:layout_below="@+id/number"
        android:layout_marginLeft="0dp"
        android:layout_marginTop="42dp" >

        <Button
            android:id="@+id/plus"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="@string/plus"
            android:onClick="onPlus" />

        <Button
            android:id="@+id/minus"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="@string/minus"
            android:onClick="onMinus" />

        <Button
            android:id="@+id/divide"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="@string/divide"
            android:onClick="onDivide" />

        <Button
            android:id="@+id/multiply"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="@string/multiply"
            android:onClick="onMultiply" />
    </TableRow>

    <TextView
        android:id="@+id/result"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignParentLeft="true"
        android:layout_alignTop="@android:id/tabs" />

</RelativeLayout>

Implementation

Now navigate to “Calculator” -> “src” -> “de.duckout.calculator” -> “MainActivity.java”. See the following coding which is commented a lot and implements the calculation logic.

package de.duckout.calculator;

import android.app.Activity;
import android.os.Bundle;
import android.view.Menu;
import android.view.View;
import android.widget.EditText;
import android.widget.TextView;

public class MainActivity extends Activity {

	private EditText inputNumber;
	private TextView outputResult;

	public void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);
		setContentView(R.layout.activity_main);

		// These Button have been initialized in the activity_main.xml
		inputNumber = (EditText) findViewById(R.id.number);
		outputResult = (TextView) findViewById(R.id.result);
	}

	@Override
	public boolean onCreateOptionsMenu(Menu menu) {
		getMenuInflater().inflate(R.menu.activity_main, menu);
		return true;
	}

	// This handles the click of the plus button
	// we specified this method in the activity_main.xml
	public void onPlus(View view) {
		float res = this.getInputNumber() + this.getCurrentResult();
		this.outputResult.setText(String.valueOf(res));
	}

	// This handles the click of the minus button
	// we specified this method in the activity_main.xml
	public void onMinus(View view) {
		float res = this.getCurrentResult() - this.getInputNumber();
		this.outputResult.setText(String.valueOf(res));
	}

	// This handles the click of the divide button
	// we specified this method in the activity_main.xml
	public void onDivide(View view) {
		// you shouldn't divide with 0
		if (this.getInputNumber() > 0) {
			float res = this.getCurrentResult() / this.getInputNumber();
			this.outputResult.setText(String.valueOf(res));
		}
	}

	// This handles the click of the multiply button
	// we specified this method in the activity_main.xml
	public void onMultiply(View view) {
		float res = this.getInputNumber() * this.getCurrentResult();
		this.outputResult.setText(String.valueOf(res));
	}

	// returns the input number
	private float getInputNumber() {
		if (this.inputNumber.getText().length() == 0) {
			return 0;
		}

		// the input is given through the .getText() method of the Edittext
		return Float.parseFloat(this.inputNumber.getText().toString());
	}

	// returns the current result
	private float getCurrentResult() {
		if (this.outputResult.getText().length() == 0) {
			return 0;
		}

		// the result is given through the .getText() method of the TextView
		return Float.parseFloat(this.outputResult.getText().toString());
	}
}

Sources: Android Developers

Der Beitrag Android Calculator erschien zuerst auf Duckout.