Select File -> New -> Other -> Android -> Android Project and create the Android project "de.vogella.android.temperature". Maintain the following.

Press "Finish". This should create the following directory structure.

While "res" contains structured values which are known to the Android platform the directory "assets" can be used to store any kind of data. In Java you can access this data via the AssetsManager and the method getAssets().

The Android SDK allows to maintain certain artifacts, e.g. strings and UI's, in two ways, via a rich editor and directly via XML. The following description tries to use the rich UI but for validation lists also the XML. You can switch between the two things the the tab on the lower part of the screen. For example in the Package Explorer select "res/layout/main.xml".

Android allows you to create attributes for resources, e.g. for strings and / or colors. These attributes can be used in your UI definition via XML or in your Java source code.

Select the file "res/values/string.xml" and press "Add". Select "Color" and maintain "myColor" as the name and "#3399CC" as the value.

Add also the following "String" attributes. String attributes allow to translate the application at a later point.

Switch to the XML representation and validate that you maintained the values correctly.

				
<?xml version="1.0" encoding="utf-8"?>
<resources>
	<string name="hello">Hello World, Convert!</string>
	<string name="app_name">Temperature Converter</string>
	<color name="myColor">#3399CC</color>
	<string name="myClickHandler">myClickHandler</string>
	<string name="celsius">to Celsius</string>
	<string name="fahrenheit">to Fahrenheit</string>
	<string name="calc">Calculate</string>
</resources>
			

Select "res/layout/main.xml" and open the Android editor via a double-click. This editor allows you to maintain the UI via drag and drop or directly via the XML source code. You can switch between both representations via the tabs at the bottom of the editor. For changing the postion and grouping elements you can use the outline view.

Delete the "Hello World, Hello!" via a right mouse click. From the "Views" bar, drag in an "EditText". Add from the layout a "RadioGroup" with two RadioButtons (you may have to delete one RadioButton), add one "Button". The result should look like the following and the corresponding XML is listed below. Make sure that your code is the same as listed below.

Switch to "main.xml" and verify that your XML looks like the following.

				
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
	android:orientation="vertical" android:layout_width="fill_parent"
	android:layout_height="fill_parent">
	<EditText android:layout_height="wrap_content" android:id="@+id/editText1"
		android:layout_width="match_parent" android:text="EditText"></EditText>
	<RadioGroup android:layout_height="wrap_content" android:id="@+id/radioGroup1"
		android:layout_width="match_parent">
		<RadioButton android:text="RadioButton"
			android:layout_width="wrap_content" android:id="@+id/radio0"
			android:layout_height="wrap_content" android:checked="true"></RadioButton>
		<RadioButton android:text="RadioButton"
			android:layout_width="wrap_content" android:id="@+id/radio1"
			android:layout_height="wrap_content"></RadioButton>
	</RadioGroup>
	<Button android:text="Button" android:id="@+id/button1"
		android:layout_width="wrap_content" android:layout_height="wrap_content"></Button>
</LinearLayout>

			

If you select a UI element you can change its properties via the properties view. Most of the properties can also be changed via the right mouse menu. Select the EditText field, right mouse click on it, select Properties-> Text and delete the content. This means no text will be initially shown in the text field.

Delete the text property in the EditText ()

Assign the "celsius" string attribute to your "text" property of the first radio button and "fahrenheit" to the second.

From now on I assume you are able to use the properties menu on the UI elements. Set the property "Checked" to true for the first RadioButton. Assign "calc" to the text property of your button and assign "myClickHandler" to the "onClick" property. Set the "Input type" property to "numberSigned" and "numberDecimal" on your EditText.

Select the backgroud (your ViewGroup / LinearLayout) and set the property "Background" to the color attribute "@color/myColor".

Switch to the "main.xml" tab and verify that the XML is correctly maintained.

				
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
	android:orientation="vertical" android:layout_width="fill_parent"
	android:layout_height="fill_parent" android:background="@color/myColor">
	<EditText android:layout_height="wrap_content" android:id="@+id/editText1"
		android:layout_width="match_parent" android:inputType="numberDecimal|numberSigned"></EditText>
	<RadioGroup android:layout_height="wrap_content" android:id="@+id/radioGroup1"
		android:layout_width="match_parent">
		<RadioButton android:layout_width="wrap_content"
			android:id="@+id/radio0" android:layout_height="wrap_content"
			android:text="@string/celsius" android:checked="true"></RadioButton>
		<RadioButton android:layout_width="wrap_content"
			android:id="@+id/radio1" android:layout_height="wrap_content"
			android:text="@string/fahrenheit"></RadioButton>
	</RadioGroup>
	<Button android:id="@+id/button1" android:layout_width="wrap_content"
		android:layout_height="wrap_content" android:text="@string/calc"
		android:onClick="myClickHandler"></Button>
</LinearLayout>

			

Change your code in "Convert.java" to the following. Note that the "myClickHandler" will be called based on the "On Click" property of your button.

				
package de.vogella.android.temperature;

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 Convert extends Activity {
	private EditText text;

	@Override
	public void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);
		setContentView(R.layout.main);
		text = (EditText) findViewById(R.id.editText1);

	}

	// This method is called at button click because we assigned the name to the
	// "On Click property" of the button
	public void myClickHandler(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)));
			} else {
				text.setText(String
						.valueOf(convertCelsiusToFahrenheit(inputValue)));
			}
			// Switch to the other button
			if (fahrenheitButton.isChecked()) {
				fahrenheitButton.setChecked(false);
				celsiusButton.setChecked(true);
			} else {
				fahrenheitButton.setChecked(true);
				celsiusButton.setChecked(false);
			}
			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;
	}
}

			

To start the Android Application, select your project, right click on it, Run-As-> Android Application Be patient, the emulator starts up very slow. You should get the following result.

Type in a number, select your conversion and press the button. The result should be displayed and the other option should get selected.

If you press the Home button you can also select your application.