Android app development - Temperature Converter

We displayed our "Hello world!" message in our last post. Now, we'll get our hands on some basic coding. We'll be doing our very own converter app that converts temperature from degree Celsius to Fahrenheit and vice-versa.

We'll start off with a New Android Application.

Create some custom icon for the launcher, like the one below.

Use a blank template for the app and click finish.

We will now create some static attributes for the elements that are going to hold our temperature values. We can also add the static attribute for color, to change the background color of the app.
To add an element, open the file res/values/strings.xml and press the add button.

Now select the Color entry as shown.

Edit the attributes for the Color attribute.

Similarly, create three more String attributes with the following values.

The below image shows the created static attributes placed besides the automatically generated xml code.

Now switch to layout editor by double clicking the activity_main.xml and then switching to Graphical Layout. Right click on the "Hello world!" text and select delete option to delete it. Now add a text field by dragging and dropping the text field box into the layout of the application. Also, drag a RadioGroup and one push button from the Form Widgets tab as shown. Delete one of the radio buttons, as we'll require only two of the three buttons.

Next, we'll proceed by assigning the static attributes which we had previously created to these user interfaces. We'll begin by right clicking on the first radio button and selecting the edit text option.

Select the string attribute "celsius" in the Resource Chooser and click OK.

Similarly assign the attributes "fahrenheit" and "calc" to the second radio button and the push button respectively. Set the checked property of the first radio button to true by right clicking on it.

Set the Input type property of the text input field to numberSigned and numberDecimal.

Now, we'll create the main program. Open the MainActivity.java from the src folder. Type the following code and save the program.

package com.example.temperatureconverter;

import android.app.Activity;
import android.os.Bundle;
import android.view.View;
import android.widget.EditText;
import android.widget.RadioButton;
import android.widget.Toast;
public class MainActivity extends Activity {
private EditText text;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
text = (EditText) findViewById(R.id.editText1);
}
// This method is called at button click because we assigned the name to the
// "OnClick property" of the button
public void onClick(View view) {
switch (view.getId()) {
case R.id.button1:
RadioButton celsiusButton = (RadioButton) findViewById(R.id.radio0);
RadioButton fahrenheitButton = (RadioButton) findViewById(R.id.radio1);
if (text.getText().length() == 0) {
Toast.makeText(this,"Please enter a valid number",
Toast.LENGTH_LONG).show();
return;
}
float inputValue = Float.parseFloat(text.getText().toString());
if (celsiusButton.isChecked()) {
text.setText(String.valueOf(convertFahrenheitToCelsius(inputValue)));
celsiusButton.setChecked(false);
fahrenheitButton.setChecked(true);
} else{
text.setText(String.valueOf(convertCelsiusToFahrenheit(inputValue)));
fahrenheitButton.setChecked(false);
celsiusButton.setChecked(true);
}
break;
}
}
// Converts to celsius
private float convertFahrenheitToCelsius(float fahrenheit) {
return ((fahrenheit - 32) * 5 / 9);
}
// Converts to fahrenheit
private float convertCelsiusToFahrenheit(float celsius) {
return ((celsius * 9) / 5) + 32;
}
}