Shoeb's musing on code and craft

First I have a class called GPSTracker that handles all the functionality related to location tracking.

package com.example.gpstracking;

import android.app.AlertDialog;
import android.app.Service;
import android.content.Context;
import android.content.DialogInterface;
import android.content.Intent;
import android.location.Location;
import android.location.LocationListener;
import android.location.LocationManager;
import android.os.Bundle;
import android.os.IBinder;
import android.provider.Settings;
import android.util.Log;

public class GPSTracker extends Service implements LocationListener {

 private final Context mContext;

 // flag for GPS status
 boolean isGPSEnabled = false;

 // flag for network status
 boolean isNetworkEnabled = false;

 // flag for GPS status
 boolean canGetLocation = false;

 Location location; // location
 double latitude; // latitude
 double longitude; // longitude

 // The minimum distance to change Updates in meters
 private static final long MIN_DISTANCE_CHANGE_FOR_UPDATES = 10; // 10 meters

 // The minimum time between updates in milliseconds
 private static final long MIN_TIME_BW_UPDATES = 1000 * 60 * 1; // 1 minute

 // Declaring a Location Manager
 protected LocationManager locationManager;

 public GPSTracker(Context context) {
  this.mContext = context;
  getLocation();
 }

 public Location getLocation() {
  try {
   locationManager = (LocationManager) mContext
     .getSystemService(LOCATION_SERVICE);

   // getting GPS status
   isGPSEnabled = locationManager
     .isProviderEnabled(LocationManager.GPS_PROVIDER);

   // getting network status
   isNetworkEnabled = locationManager
     .isProviderEnabled(LocationManager.NETWORK_PROVIDER);

   if (!isGPSEnabled && !isNetworkEnabled) {
    // no network provider is enabled
   } else {
    this.canGetLocation = true;
    if (isNetworkEnabled) {
     locationManager.requestLocationUpdates(
       LocationManager.NETWORK_PROVIDER,
       MIN_TIME_BW_UPDATES,
       MIN_DISTANCE_CHANGE_FOR_UPDATES, this);
     Log.d("Network", "Network");
     if (locationManager != null) {
      location = locationManager
        .getLastKnownLocation(LocationManager.NETWORK_PROVIDER);
      if (location != null) {
       latitude = location.getLatitude();
       longitude = location.getLongitude();
      }
     }
    }
    // if GPS Enabled get lat/long using GPS Services
    if (isGPSEnabled) {
     if (location == null) {
      locationManager.requestLocationUpdates(
        LocationManager.GPS_PROVIDER,
        MIN_TIME_BW_UPDATES,
        MIN_DISTANCE_CHANGE_FOR_UPDATES, this);
      Log.d("GPS Enabled", "GPS Enabled");
      if (locationManager != null) {
       location = locationManager
         .getLastKnownLocation(LocationManager.GPS_PROVIDER);
       if (location != null) {
        latitude = location.getLatitude();
        longitude = location.getLongitude();
       }
      }
     }
    }
   }

  } catch (Exception e) {
   e.printStackTrace();
  }

  return location;
 }
 
 /**
  * Stop using GPS listener
  * Calling this function will stop using GPS in your app
  * */
 public void stopUsingGPS(){
  if(locationManager != null){
   locationManager.removeUpdates(GPSTracker.this);
  }  
 }
 
 /**
  * Function to get latitude
  * */
 public double getLatitude(){
  if(location != null){
   latitude = location.getLatitude();
  }
  
  // return latitude
  return latitude;
 }
 
 /**
  * Function to get longitude
  * */
 public double getLongitude(){
  if(location != null){
   longitude = location.getLongitude();
  }
  
  // return longitude
  return longitude;
 }
 
 /**
  * Function to check GPS/wifi enabled
  * @return boolean
  * */
 public boolean canGetLocation() {
  return this.canGetLocation;
 }
 
 /**
  * Function to show settings alert dialog
  * On pressing Settings button will lauch Settings Options
  * */
 public void showSettingsAlert(){
  AlertDialog.Builder alertDialog = new AlertDialog.Builder(mContext);
     
        // Setting Dialog Title
        alertDialog.setTitle("GPS is settings");
 
        // Setting Dialog Message
        alertDialog.setMessage("GPS is not enabled. Do you want to go to settings menu?");
 
        // On pressing Settings button
        alertDialog.setPositiveButton("Settings", new DialogInterface.OnClickListener() {
            public void onClick(DialogInterface dialog,int which) {
             Intent intent = new Intent(Settings.ACTION_LOCATION_SOURCE_SETTINGS);
             mContext.startActivity(intent);
            }
        });
 
        // on pressing cancel button
        alertDialog.setNegativeButton("Cancel", new DialogInterface.OnClickListener() {
            public void onClick(DialogInterface dialog, int which) {
            dialog.cancel();
            }
        });
 
        // Showing Alert Message
        alertDialog.show();
 }

 @Override
 public void onLocationChanged(Location location) {
 }

 @Override
 public void onProviderDisabled(String provider) {
 }

 @Override
 public void onProviderEnabled(String provider) {
 }

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

 @Override
 public IBinder onBind(Intent arg0) {
  return null;
 }

}

Now comes my android activity

package com.example.gpstracking;

import android.app.Activity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.Toast;

public class AndroidGPSTrackingActivity extends Activity {
 
 Button btnShowLocation;
 
 // GPSTracker class
 GPSTracker gps;
 
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        
        btnShowLocation = (Button) findViewById(R.id.btnShowLocation);
        
        // show location button click event
        btnShowLocation.setOnClickListener(new View.OnClickListener() {
   
   @Override
   public void onClick(View arg0) {  
    // create class object
          gps = new GPSTracker(AndroidGPSTrackingActivity.this);

    // check if GPS enabled  
          if(gps.canGetLocation()){
           
           double latitude = gps.getLatitude();
           double longitude = gps.getLongitude();
           
           // \n is for new line
           Toast.makeText(getApplicationContext(), "Your Location is - \nLat: " + latitude + "\nLong: " + longitude, Toast.LENGTH_LONG).show(); 
          }else{
           // can't get location
           // GPS or Network is not enabled
           // Ask user to enable GPS/network in settings
           gps.showSettingsAlert();
          }
    
   }
  });
    }
    
}

Now comes my layout, main.xml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:orientation="vertical" >
    
    <Button android:id="@+id/btnShowLocation" 
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Show Location"
        android:layout_centerVertical="true"
        android:layout_centerHorizontal="true"/>

</RelativeLayout>

Finally, this is my android manifest

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.example.gpstracking"
    android:versionCode="1"
    android:versionName="1.0" >

    <uses-sdk android:minSdkVersion="8" />

    <application
        android:icon="@drawable/ic_launcher"
        android:label="@string/app_name" >
        <activity
            android:name=".AndroidGPSTrackingActivity"
            android:label="@string/app_name" >
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
    </application>
    
 <uses-permission android:name="android.permission.ACCESS_FINE_LOCATION" /> 
 <uses-permission android:name="android.permission.INTERNET" />

</manifest>

Javascript has no classes. Everything is an object in Javascript. Even functions. And objects can inherit other objects.

In this post, I will show how to use this unique inheritance feature of Javascript, aka prototypal inheritance, to customize built in Javascript objects like arrays. Particularly, I will show how to add a custom method to the Javascript Array object so that any array you use in your javascript app can use that method.

Whenever you create a new array in Javascript, it is an object inheriting from the Array object. Our target is to add a search method to the Array object. Wouldn’t it be convenient to be able to search arrays like

var result = myArray.find("Mango"); Well, wouldn’t it?

You bet it will be. But Javascript arrays do not come with a find method. Let us put it into the Array object so that all arrays can use it.

Array.prototype.find = function(key, value)
{
   var i;

   if(!key && !value)
   {
      return this;   //return the whole array since no parameters are passed
   }

   for(i = 0; i < this.length; i++)
   {
      if(!value)
      {
         //if only one parameter is passed, it will be found as key, value will be null

         value = key;

         if(this[i] == value) return this[i];
      }
      else
      {
         if(this[i][key] == value) return this[i];
      }
   }

   return null;
}

The code has been generalized to work for both complex objects in the target array, as well as simple arrays like an array of strings. If your array has complex objects then obviously you have to pass an extra parameter to the search function telling which property of an object will be searched for a matching value.

The use of the keyword prototype in the function declaration makes this function available to all sub-objects of Array, i.e. all arrays in your Javascript app. In the same way, you could add a variable to Array. And you can put any object before the prototype keyword. That is the beauty of Javascript’s prototypal inheritance; the hierarchy can start from anywhere.

If you have ever worked with ArrayLists or Vectors in C# or Java (these are expandable arrays, for those who do not know), you will have noticed that ArrayList or Vector class comes in with lots and lots of helper methods like toString(), find() for manipulating the arrays. Javascript does not give you so many helper methods built-in. But using prototypal inheritance, you can very easilly add helper methods like these and make your arrays more fun to use.

Shoeb's musing on code and craft

Monday, March 21, 2016

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