Android App Development 201 1st tutorial; Android and Web Service, Multi Threading using AsyncTask and More

In this tutorial, we will look at multi threading in android using Async Task as well as how to integrate web service with your android application. We will look at new API's such as location manager to get the location information using the GPS sensor. We will then convert the location information to a Json Object and pass that object to a url using Http POST request. Here is the code:


package com.example.locationtest;

import java.io.IOException;
import java.io.UnsupportedEncodingException;
import java.util.Timer;
import java.util.TimerTask;
import org.apache.http.client.ClientProtocolException;
import org.apache.http.client.HttpClient;
import org.apache.http.client.methods.HttpPost;
import org.apache.http.entity.StringEntity;
import org.apache.http.impl.client.DefaultHttpClient;
import org.json.JSONException;
import org.json.JSONObject;
import android.location.Location;
import android.location.LocationListener;
import android.location.LocationManager;
import android.os.AsyncTask;
import android.os.Bundle;
import android.os.Handler;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;
import android.widget.Toast;
import android.app.Activity;
import android.content.Context;
import android.content.Intent;


public class MainActivity extends Activity implements LocationListener{
private TextView textView =null;
LocationManager locationManager=null;
Location location=null;
protected String url;
protected JSONObject jsonData=null;
private EditText urlText=null;

@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
locationManager = (LocationManager)getSystemService(Context.LOCATION_SERVICE);
final boolean gpsEnabled = locationManager.isProviderEnabled(LocationManager.GPS_PROVIDER);
if(gpsEnabled!=true) {
Toast.makeText(getApplicationContext(), "GPS Disbled! Please Enable to Proceed!", Toast.LENGTH_SHORT).show();
        startActivity(new Intent(android.provider.Settings.ACTION_LOCATION_SOURCE_SETTINGS));
}

textView = (TextView)findViewById(R.id.textView);
locationManager.requestLocationUpdates(LocationManager.GPS_PROVIDER, 0, 1, this);
urlText = (EditText)findViewById(R.id.urlTextbox);
Button submitButton = (Button)findViewById(R.id.submitUrl);

submitButton.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View view) {
if (urlText.getText()!=null) {
url=urlText.getText().toString();
System.out.println(url);//for testing only, not required
Toast.makeText(getApplicationContext(), "Url Submitted, Sending data to Web Service at url: " + url, Toast.LENGTH_SHORT).show();
}
}
});




}

@Override
public void onLocationChanged(final Location location) {
this.location=location;
final Handler handler = new Handler();
 Timer ourtimer = new Timer();
 TimerTask timerTask = new TimerTask() {
 int cnt=1;  
 public void run() {
                 handler.post(new Runnable() {
                         public void run() {
                       
                        Double latitude = location.getLatitude();
                      Double longitude = location.getLongitude();
                      Double altitude = location.getAltitude();
                      Float accuracy = location.getAccuracy();
                      textView.setText("Latitude: " + latitude + "\n" + "Longitude: " + longitude+ "\n" + "Altitude: " + altitude + "\n" + "Accuracy: " + accuracy + "meters"+"\n" + "Location Counter: " + cnt);
                      try {
                      jsonData = new JSONObject();
jsonData.put("Latitude", latitude);
jsonData.put("Longitude", longitude);
jsonData.put("Altitude", altitude);
jsonData.put("Accuracy", accuracy);

System.out.println(jsonData.toString());//not required, for testing only
if(url!=null) {
new HttpPostHandler().execute();
}
} catch (JSONException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
                     
                      cnt++;
                         }
               
                });
         }};
     ourtimer.schedule(timerTask, 0, 120000);

}

@Override
public void onProviderDisabled(String provider) {


}

@Override
public void onProviderEnabled(String provider) {


}

@Override
public void onStatusChanged(String provider, int status, Bundle extras) {


}





public class HttpPostHandler extends AsyncTask<Void,Void,Void> {

@Override
protected Void doInBackground(Void... arg0) {

HttpClient httpClient = new DefaultHttpClient();
HttpPost httpPost = new HttpPost(url);
StringEntity dataEntity = null;
try {
dataEntity = new StringEntity(jsonData.toString());
} catch (UnsupportedEncodingException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
httpPost.setEntity(dataEntity);
httpPost.setHeader("Content-Type", "application/json");
try {
httpClient.execute(httpPost);
} catch (ClientProtocolException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();

}
return null;


}

@Override
protected void onPostExecute(Void result) {
// TODO Auto-generated method stub
super.onPostExecute(result);
try {
this.finalize();
} catch (Throwable e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}

}

}

Here is the layout code:

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical" >
 
    <EditText
        android:id="@+id/urlTextbox"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:hint="Web Service Url"
    android:layout_gravity="top"
        />
    <Button android:id="@+id/submitUrl"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Submit"
        android:layout_gravity="right"
/>
 
    <TextView
        android:id="@+id/textView"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text=""
        android:layout_gravity="center"/>
 
</LinearLayout>

As you can see in the code, at first it makes sure the GPS is turned or it will launch the activity to the location settings menu. Once it makes sure the GPS is enabled, it starts getting location and displaying them in the textview. Once we enter the url to send the post information in the edit text, it starts sending location information to the url using Http POST. Remember to add following permissions to your android manifest file.

<uses-permission android:name="android.permission.ACCESS_COARSE_LOCATION" />
<uses-permission android:name="android.permission.ACCESS_FINE_LOCATION" />
<uses-permission android:name="android.permission.INTERNET" />

Complete source code is available here

Android App Development 101 5th tutorial; Android and Web, Turn your Web Site into an Android App!

In this tutorial, I will be using Android WebView to display my blog in our android app. Web View is very straight forward and offer several features. We will be looking at few of them. At first we need to make a layout in xml with our WebView object, then we will load our url into the layout.

activity_main.xml


<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"

    android:layout_width="match_parent"
    android:layout_height="match_parent"
 android:orientation="vertical"
 >

    <WebView
        android:id="@+id/webview"
        android:layout_width="fill_parent"
        android:layout_height="fill_parent"
      />

</LinearLayout>


MainActivity.java


package com.example.webview;

import android.os.Bundle;
import android.app.Activity;
import android.view.KeyEvent;
import android.webkit.WebView;
import android.webkit.WebViewClient;

public class MainActivity extends Activity {
WebView ourwebView;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
loadWeb();
}

public void loadWeb() {
WebView webView = (WebView)findViewById(R.id.webview);
ourwebView=webView;
this.setTitle("Android Happenings");
ourwebView.setWebViewClient(new WebViewClient());
String url="http://androidhappenings.blogspot.com/";
ourwebView.canGoBack();
ourwebView.loadUrl(url);

}


public boolean onKeyDown(int keyCode, KeyEvent event) {
if (keyCode==KeyEvent.KEYCODE_BACK && ourwebView.canGoBack()) {
ourwebView.goBack();
return true;

}
return super.onKeyDown(keyCode, event);
}


}

As we can see in the above java code, the onKeyDown method checks for back presses and move our web view one page back in each back press whenever possible. Also make sure that you add internet permission in your manifest or it will display web page not found error.
<uses-permission android:name="android.permission.INTERNET" />

Android App Development 101 4th tutorial; Developing Android StopWatch/Timer

In this tutorial, i will be making a stop watch for android. We will create a text view to display the time elapsed and two buttons one to start the timer and second to stop the timer. We will be using more xml attributes and new java concepts such as runnables and handlers. In addition we will be using android Timer class. Here is our layout:

main.xml


<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"

    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:orientation="vertical" >

      <TextView
        android:id="@+id/androidtimer"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:gravity="center"
        android:text="Android Timer"
        android:textSize="40sp"
        android:textStyle="bold"
        android:textColor="#FF0000"/>
   
    <LinearLayout
        android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="horizontal"
    android:gravity="bottom|center" >
    <Button
        android:id="@+id/start"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:background="#FF0000"
        android:text=" start "
        android:textSize="35sp"
        android:textColor="#FFFFFF"
        android:onClick="startTimer"
/>
    <View
        android:layout_width="20dp"
        android:layout_height="1dp"/>
       <Button
        android:id="@+id/stop"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:background="#FF0000"
        android:text=" stop "
        android:textSize="35sp"
        android:textColor="#FFFFFF"
        android:onClick="stopTimer"
       
/>
       </LinearLayout>
</LinearLayout>

The View objects are used just to create some space between two buttons. Also you can see that we have used a new linear layout within a linear layout to display two buttons in a horizontal row.

TimerActivity.java


package com.example.timer;

import java.util.Timer;
import java.util.TimerTask;
import android.os.Bundle;
import android.os.Handler;
import android.app.Activity;
import android.view.View;
import android.widget.TextView;

public class TimerActivity extends Activity {
TimerTask timerTask;
int n=0;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
}

public void startTimer(View view) {
final Handler handler = new Handler();
Timer ourtimer = new Timer();
timerTask = new TimerTask() {
       public void run() {
               handler.post(new Runnable() {
                       public void run() {
                  TextView timer = (TextView)findViewById(R.id.androidtimer);
               
                  timer.setText(n + " Seconds");
                      n++;
                       }
              });
       }};


   ourtimer.schedule(timerTask, 0, 1000);

}
public void stopTimer(View view) {
timerTask.cancel();
timerTask=null;
n=0;
}

}