[align=center]The Friend Finder - MapActivity using GPS - Part: I / II [/align]
[align=center]See also: >> Part II / II <<[/align]
[align=center]View: >> Full Source for this Tutorial <<[/align]

What is this: This tutorial shows how to create a relatively complex application, that takes advantage of LocationManager (GPS-Access), to show your contacts on a Map.

What you will learn:

• You will learn how to extend the MapActivity to create a Map-Application.
• Use the LocationManager to track your GPS-Position.
• Work with Cursors to grab data from the contents.
• Override the onFreeze(), onResume(), onXYZ()-methods which are i.e. called, when another activity gets on top of ours.
• Draw things on the MapView using an OverlayController.
• How to create menus.
• Many more.....

Problems/Questions: post right below...

Difficulty: 3.5 of 5

What it will look like:
1. Always updating Screen
2. FriendFinder-Map toggled to SatelliteView
3. FriendFinder-Map toggled to Streets-View (also updating ^^ own position got outside of the map)
[align=center]
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Description:
So the first thing as always is, to think about what we want to do and what we need for that...

• We want a ListView of our Contacts --> We need a ListView (awesome conclusion... )
• We want to do sth. with geo-Location(GPS) --> We need a LocationManager and his friends
• We want to get the location of our friends --> We need a place to define them!
• We want to display a Map --> We need a second (Map)Activity
  a. We need to register that second Activity
• We want to draw sth over the Map --> We need an OverlayController

As we need to store the GPS-Location of our contacts somewhere, I chose the Notes-Section in each Contacts-Profile. Saving a GPS-location is pretty simple, as we choose a well-structured style of data: a URI-String, which can easily found and extracted from the Notes-String using Regular Expressions. (all that is explained in details below)

[align=center] As a human you can see the format of the URI: "geo:[-]XXX.XXXXX,[-]XXX.XXXXXX#".
Simply setup two or three sample-contacts (with different GPS-Locations) just like in the image below.
Or take these:
geo:37.402346,-122.075014# (Google-Headquarters, SF, California)
geo:37.444608,-122.216034# (McDonalds, near MountainView, SF, California)
geo:37.41622,-122.089919# (Starbucks, somewhere in SF, California)
or get your own on GoogleMaps (Hover the "Link to this Page"-Link)
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[align=center]>> Part I / II <<[/align]
[align=center]GoTo: >> Part II / II <<[/align]

0. Create an new Android-Project (HowTo).
I called it "FriendFinder" as that is an extremely perfect name

As we are planning to access the Contacts of our Android-Phone, we make that public in the AndroidManifest.xml . If we wouldn't do that, our Application would 'crash'(Exception followed by App-End) right when we would try to access the Contacts for the first time.

<?xml version="1.0" encoding="utf-8"?>

We need to define all the Strings we are going to use in our application in the 'res/values/strings.xml'.
(We could hardcode them too, but that would be very bad )


We will also have a class: 'Friend' (in Friend.java) which combines a Name with a Location:


1. So lets start where all Activities start:


2. Lets dig deeper into the refreshFriendsList()-Method, which will grab our Contacts/Friends out of Androids Database using a query/Cursor.
As it is a pretty big function doing some advanced logic, we will split into pieces here.

The first thing we will do is to grab a so called Cursor. I'll try to explain that referring to relational databases and their SQL (Structured Query Language).
A Cursor is kinda like the result of a SQL-Query. In this case we make a query on 'People.CONTENT_URI' what would referr to sth. like 'SELECT * FROM 'Contacts'.
The next 3 arguments remain 'null', we could have filled them stuff like the equivalent to 'WHERE Name='Peter''...
The last field contains the Sort-Order we want to receive. Here the similarity to SQL is pretty obvious. We chose sorting the results by People.NAME in an ASCending order.

We are now going to loop through every contact that the Cursor found/'is providing' and check whether the Notes-String of that Contact somwhere contains a 'geo:XX...XX#' within.

If there was anything saved within the Notes of this contact, we now check whether there is a 'geo:XX...XX#' within the Notes-String. If we wound one, we extract the Latitude/Longitude and save it to 'friendLocation'.
[align=center]Learn about Regular Expressions in Java.[/align]

So, if the friendLocation is passed can be not null (if we found a 'geo...# within the notes), but can also be still as we found nothing. Now we close the loop to iterate over every Contact.

All of our friends are now stored to the field 'this.allFriends'.

3. Now lets hop into the next function that had been called in onCreate(...):

This method will display all contacts + their distance to ourself, as you've seen it in the animated GIF above.
The first thing we are doing with in is to get our own GPS-Location.
Question: How will that work, we are in an emulator, with no gps-receiver connected
Answer: Within the emulator there is running a pseudo-gps-receiver, that simulates a person driving/walking around in San Francisco, close to the Google-Headquarters!

So, 'this.myLocation' is of the type "Location" which now contains mainly a "Longitude and Latitude"-Value, what together is our exact location on planet earth.

Now we loop over 'this.allFriends' and determine our distance towards each and save it in a ArrayList<String>, IF they are not farer away than the static field: NEARFRIEND_MAX_DISTANCE.

Now we only have to apply that ArrayList<String> to be put into our ListView (what we can see actually) with the following lines:


We could start our Application by now but the values would not yet update. But as we want them to update like this:
[align=center][/align]
We need to do some more "System"-Stuff. Don't panic, there will be ~3x comments than Lines of real code.

4. Remembering the onCreate(..)-method from the very beginning, there was another method left within:


So lets get into that heavily commented function:

We used the following specialized IntentReceiver above, that will simply call our updateList()-method when it receives an Intent. (As we will apply our filter to it, it will only receive 'MY_LOCATION_CHANGED_ACTION'-Intents)
The following to Classes/Objects were used above and are working "as a team" :
"( registerReceiver(this.myIntentReceiver, this.myIntentFilter); ")


5. The last thing we would have to do is to overwrite the onResume() and onFreeze(...)-Functions, as we want to (un)register as the Application is the top-most or not. (Prevents unnecessary CPU-Usage and therefor Battery-Consumption).
[align=center]:idea: For further information about those onWhatEver()-Methods have a look here: Lifecycle of an Activity.[/align]


[align=center]You find the full code at the very very very end of this post.
:!: Congratulations, you've just created a auto-refreshing, gps-using Killer-Application [/align]

But this was just the first part! We want to do some Map-Stuff

[align=center]GoTo: >> Part II / II <<[/align]

[align=center]View: >> Full Source for this Tutorial <<[/align]

Regards,
plusminus

As it is a pretty big function doing some advanced logic, we will split into peaces here.

s/peaces/pieces/g

We chosse sorting the results by People.NAME in an ASCending order.

s/chosse/chose/g

Excellent tutorial, by the way. Thanks.

Tom

P.S. Not trying to be picky, just pointing out some typos...

Hello aetmos,

awww no, those typos were really painful
Definitely a result of less sleep in that time

Regards,
plusminus

Thanks plusminus for the excellent tutorial! It was really helpful.

I'd like to say thank you for that great app. I'm diving into the Android experience and you're tutorials are very helpful.

As the Interface for the contacts seems to have changed (your screenshot which shows "Notes" looks completely different) i have a few questions:
1. when adding a contact, i noticed i can add custom fields to contacts. Obviously i could just create a "Gps" field with the location. But how do i access those custom fields within a cursor? Also, i'm wondering how this is working, as some contacts may have a gps field, others may not. From the SQL point of view there are two possibilites: Android adds a new column to the contacts which could result in many unused fields on other contacts. Or it could create a foreign table.. Anyways i'm wondering how i get this data.
The line of interest would be: "int notesColumn = c.getColumnIndex(People.NOTES); "
Obviously People.GPS doesnt work..

Thank you in advance (and for this great site!)

Sebastian

Hi Sebastian

I have the same issue, I created the custom fiel Notes but the function
int notesColumn = c.getColumnIndex(People.NOTES); return 1 and the string inside is null

It does not work as you wrote, if you find the solution let me know
BR
CA

buster wrote:As the Interface for the contacts seems to have changed (your screenshot which shows "Notes" looks completely different) i have a few questions:
1. when adding a contact, i noticed i can add custom fields to contacts. Obviously i could just create a "Gps" field with the location. But how do i access those custom fields within a cursor? Also, i'm wondering how this is working, as some contacts may have a gps field, others may not. From the SQL point of view there are two possibilites: Android adds a new column to the contacts which could result in many unused fields on other contacts. Or it could create a foreign table.. Anyways i'm wondering how i get this data.
The line of interest would be: "int notesColumn = c.getColumnIndex(People.NOTES); "
Obviously People.GPS doesnt work..

Thank you in advance (and for this great site!)

Sebastian

Can you tell me where should the contacts be added for the FriendFinder application to work, i see this error .

Application Error:
com.android.friendfinder

An error has occured in com.android.friendfinder.
Unable to start activity
ComponenetInfo{com.android.friendfinder/com.andorid.friendfinder.FriendFinder}:
java.lang.SecurityException:
Permission
android.permission.READ_CONTACTS required for provider contacts.

i tried adding contacts name as the geo location but doesn thelp


thanks,
devang

you need to add the proper permission in your manifest.xml as the error already says
Open the Manifest.xml in Eclipse (you should see some good UI coming up, the Manifest Editor) and add that permission to your Activity.

Just have a Question for your Friend Nearby variable ...
I have the problem that i must now if this Locationpoint is the same location point i have in my Array. So I'm driving arround and if my position is in the radius of x meters or miles around a position which is in this array i'm doing something.

So I have
- me with a moving position and every x seconds i ask the array
- the array with a lot of saved positions
- a radius around the saved positions in the array (in this radius every request get true back)


Has anybody an idea in which way i can calculate this? How can i calculate the whole positions around the point which are accepted too?

Or some other ideas to solve it in a different way so that i don't need the array of fixed waypoints?

hi, i have a question. In my android library there isn't com.google.android.maps.OverlayController class. where can i find it? thanks!

zak wrote:hi, i have a question. In my android library there isn't com.google.android.maps.OverlayController class. where can i find it? thanks!

This has changed to:
com.google.android.maps.Overlay
and
com.google.android.maps.OverlayItem

Search this site for some samples.

CU!

I'm very new to Android app programming, so please forgive me if my question seems too basic.

I've found several apps that talk about mapping out friend locations, so I need to ask:

Is it possible for an app on my G1 phone to identify the current location of a friend who also has a G1 phone? In other words, is the "friend" location dynamic?

I think the answer is "no", since I don't know how an app on my phone would be able to detect the location of another person with a G phone. Just wanted to clarify that.

thanks.

How can I add the mock geo location of each contact in android sdk 1.0 rc2?

I don' see the 'Notes' Session in the contacts in the emulator.

Thank you.

Hello,
I am trying to access the phone book conatcts. It is working fine in SDK, but when ever I am trying to run it in actual phone the code is crashing.

Code:
private String CheckForNameFromContacts(String display_name)
{

try
{
Cursor c = getContentResolver().query(People.CONTENT_URI, null, null, null, null);

if (c.moveToFirst()) {

String name = null;

int phoneid = 0;

String phoneno = null;

do {

name = c.getString(c.getColumnIndex(People.NAME));

if(name.equals(display_name))

{

Toast.makeText(this,name,Toast.LENGTH_LONG);

phoneid = c.getInt(c.getColumnIndex(People.PRIMARY_PHONE_ID));

phoneno = c.getString(c.getColumnIndex(People.NUMBER));


return phoneno;
}

} while (c.moveToNext());

return null;
}
}
catch (Exception e) {
Toast.makeText(OpenSocial_Friends.this, "Exception: Couldn't access contacts"+ e.getMessage(), Toast.LENGTH_LONG).show();

return null;
}
return null;

}


Please help me getting it solved.

Regards,
Parimal.