Android apps can be developed using android studio or eclipse IDEs. For this sample, we are going to use android studio. Before we jump into project and start coding, I am going to explain few components and elements of android which are used in this project.
Each screen you interact with when you open an app is provided by an activity component. In this example, we have one screen so we will create one activity. Android system uses call back methods to inform activity about screen status changes. Activity components are defined in manifest xml file. UI layouts are defined in xml file and used in activity to set the layout for activity screens.
This example project is called distance converter. It converts distance entered into km or miles. It lets user to enter distance, select distance type and submit for conversion. Converted distance will be displayed on the same screen. If user clicks button without entering distance or selecting type, message popup will be displayed informing user about the same using Toast. Onclick event handler for the button is mentioned in the layout xml file and the event handler method is placed in the activity class.
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.firstapps.distanceconverter">
<application
android:allowBackup="true"
android:icon="@mipmap/ic_launcher"
android:label="@string/app_name"
android:supportsRtl="true"
android:theme="@style/AppTheme">
<activity android:name=".MainActivity">
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
</application>
</manifest> public class MainActivity extends AppCompatActivity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
}
public void convertDistance(View view ){
EditText editText = (EditText) findViewById(R.id.distance);
String distance = editText.getText().toString();
RadioGroup radioGroup = (RadioGroup) findViewById(R.id.rgrp);
try{
int rbid = radioGroup.getCheckedRadioButtonId();
RadioButton selectedRadioButton = (RadioButton)radioGroup.findViewById(rbid);
String disttype = selectedRadioButton.getText().toString();
String targetDistType = "";
double dist = Double.valueOf(distance);
if("Km".equals(disttype)){
dist = 0.621371 * dist;
targetDistType = getString(R.string.miles);
}else{
dist = 1.60934 * dist;
targetDistType = getString(R.string.km);;
}
TextView convertedDist = (TextView) findViewById(R.id.converted_dist);
convertedDist.setText(dist+" "+targetDistType);
}catch(Exception e){
Toast toast = Toast.makeText(getApplicationContext(), getString(R.string.errorMs), Toast.LENGTH_SHORT);
toast.show();
}
}
}
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:id="@+id/activity_main"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:paddingBottom="@dimen/activity_vertical_margin"
android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
tools:context="com.firstapps.distanceconverter.MainActivity">
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Enter Distance"
android:layout_alignParentTop="true"
android:layout_alignParentLeft="true"
android:layout_alignParentStart="true"
android:layout_marginTop="15dp"
android:id="@+id/distlable"></TextView>
<RadioGroup
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:orientation="horizontal"
android:layout_below="@+id/distance"
android:layout_marginTop="14dp"
android:gravity="center"
android:id="@+id/rgrp">
<RadioButton
android:text="Km"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:id="@+id/rb_km"></RadioButton>
<RadioButton
android:text="Miles"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:id="@+id/rb_miles"/>
</RadioGroup>
<EditText
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:inputType="number"
android:ems="10"
android:id="@+id/distance"
android:layout_marginRight="18dp"
android:layout_marginEnd="18dp"
android:layout_alignBaseline="@+id/distlable"
android:layout_alignBottom="@+id/distlable"
android:layout_alignParentRight="true"
android:layout_alignParentEnd="true"></EditText>
<Button
android:text="Convert Distance"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginTop="104dp"
android:id="@+id/convert"
android:onClick="convertDistance"
android:layout_below="@+id/rgrp"
android:layout_centerHorizontal="true"></Button>
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_below="@+id/rgrp"
android:layout_alignLeft="@+id/distance"
android:layout_alignStart="@+id/distance"
android:layout_marginTop="52dp"
android:id="@+id/converted_dist"></TextView>
</RelativeLayout>
<resources>
<string name="app_name">DistanceConverter</string>
<string name="miles">Miles</string>
<string name="km">Km</string>
<string name="errorMs">Please enter distance and select type.</string>
</resources>