Android Tutorial Android Wifi-Direct Tutorial

Erel · Jun 20, 2013

Android 4+ devices support Wifi Direct (Wifi P2p). Wifi Direct allows you to connect two devices over wireless without an access point. It is similar to Bluetooth with a much extended range and performance.

It is recommended to use Android 4.1+ devices as there are several major known issues with Android 4.04 devices and Wifi Direct.

Establishing a connection over wifi direct is done in two main steps. First you need to discover and make a peer to peer connection. This step ends when you have the IP address of the other device.

In the second step you use the Network library (together with AsyncStreams) to create a connection with the other device IP address.

Creating the peer to peer connection

First we should find the nearby peers by calling manager.DiscoverPeers.
The PeersDiscovered event will be raised when the process completes.
This event includes a list with the discovered devices. Note that this event will also be raised during the connection process so your code should be ready to handle multiple calls of this event.

Once we have a device we can call manager.Connect with the device MAC address. The ConnectionChanged event will be raised.

This event includes the group owner IP address. If the address is "127.0.0.1" then the current device is the owner. You should use a ServerSocket to accept incoming connections.

Otherwise you need a Socket to connect to the group owner ip.

The attached example implements a wifi direct connection and then allows you to send a message from one device to the other. The implementation is done with a Service. It is easier to use a Service for such tasks as the service will not be destroyed like the activity.

BTW, I did a small test to check the maximum range until the connection broke. The result was about 40 - 50 meters (tested with Galaxy Nexus and Nexus 4).

The library is available here: http://www.b4x.com/forum/additional...ates/30410-wifidirect-library.html#post176527

Erel · Dec 25, 2013

Yes. Though there are other possible solutions that may be easier to implement / use such as Bluetooth.

anaylor01 · Jan 4, 2014

Is there a code sample of that somewhere?

Erel · Jan 5, 2014

Code sample of what? There is an example in the first post.

Paulsche · Feb 14, 2014

The connection works, how can I send a file now?

Erel · Feb 16, 2014

Once there is a socket connection you can work with the socket like working with any other socket.

For example: FileTransfer - Send and receive files with AsyncStreams

Paulsche · Feb 16, 2014

Erel said:
Once there is a socket connection you can work with the socket like working with any other socket.

For example: FileTransfer - Send and receive files with AsyncStreams

Thanks

LucaMs · Feb 16, 2014

I apologize in advance for the question asked without reading everything.

it is possible that the app accept connections automatically, without user intervention?

I was thinking of an app in which the user activates a function of listening and the app analyzes the first data received and then decides whether to continue the connection.

Erel · Feb 16, 2014

Yes. Read the tutorial to understand how it works.

LucaMs · Feb 16, 2014

ok, I did not want to start without the confirmation of the possibility.

thanks

scrat · Apr 7, 2014

The library works well, thanks.

Just 2 problems:
How to disconnect from a group to connect to another.
I have to manually delete the connection in the wifi parameters to be able to reconnect

When I use manager.GetCurrentStatus I have this error

B4X:

java.lang.Exception: Sub manager_connectionchanged signature does not match expected signature.

and the subis

B4X:

Sub Manager_ConnectionChanged(Connected As Boolean, GroupOwnerIp As String)

thank you

Erel · Apr 8, 2014

The signature error is a bug that happens when there is no group. It will be fixed.

About the first problem, what happens when you call DiscoverPeers again?

scrat · Apr 8, 2014

About the first problem, what happens when you call DiscoverPeers again?

the devices list is refreshed noting more.

the scenario
Three devices "A"," B"," C" in the same room
After a Discover "A" see "B" and "C", "B" see "A" and "C" etc ...
"A" connects to "B" with "B" Mac adress and exchange something.
"A" wants to disconnect from "B" and connect to "C" in a new "AC" group (without B inside)
Howto disconnect and remove "AB" group ?

In the api doc i see removeGroup and createGroup methods.
these methods may be the solution?

Erel · Apr 8, 2014

What happens when you call connect with C address?

scrat · Apr 8, 2014

Nothing.
Device A is always connected to B

before connection with C I try to disconnect

B4X:

Public Sub Disconnect
If client.IsInitialized Then client.Close
If server.IsInitialized Then server.Close
manager.CancelConnections
End Sub

Other problem
I close and kill the app on A and B
I restart app on A et B
I try to connect to C from A and the connection is alway on A and B

Erel · Apr 8, 2014

Is the ConnectionChanged event raised when you try to connect to C?

Have you tried to dim WifiManager and initialize it again?

scrat · Apr 8, 2014

Yes it works afer close server, client and redim wifimanager

B4X:

Public Sub Init
    If server.IsInitialized Then server.Close
    If client.IsInitialized Then client.Close
    Dim server As ServerSocket
    Dim client As Socket
    Dim manager As WifiManager
    server.Initialize(port, "server")
    manager.Initialize("manager")
    UpdateUI
End Sub

Yes it works.
But I must wait a long time before reconnecting (~5")
If I connect just after WifiManager_ConnectionChanged nothing works and I must cut wifi or reboot.

luke2012 · Sep 5, 2014

Erel said:
I plan to create a mini-framework based on AsyncStreams that will make it easier to send and receive objects and files.

Hi @Erel,
the mini-framework based on AsyncStreams is available now?

Erel · Sep 7, 2014

Yes: http://www.b4x.com/android/forum/pages/results/?query=asyncstreams+objects&page=1&prefix=0

antonomase · Sep 9, 2014

Hi,

I have 2 phones A and B and 2 tablets X and Y, all in the same room. The phones are used as remote controls of the tablets.
I want to connect the phone A on the tablet X and the phone B on tablet Y.

In my App on the phones, I want to display the Mac adress of the discovered devices.

Question 1: In the device list set by the method Manager_PeersDiscovered (Success As Boolean, Devices As List), how to get the deviceAddress of each discovered device ? What type of object is in the ArrayList named Devices ?
Found : Devices is an Array of WifiDevices (need to read file WifiDirect.xml to find it)
But : Why having an object which seems to have a lot of properties and just two getters (name et MacAdddress) ?

Question 2 : On each tablet, how to display the mac Address of the wifi so the user can see which phone must be connected to the tablet ?
Found : using Library ABWifi
But : on each the device, the mac address with ABWifi begins witch 5C and with Wifi direct begins with 5E (the other digits are OK). Why ?

Thanks

Erel · Sep 9, 2014

Why having an object which seems to have a lot of properties and just two getters

Not sure that I understand the question. Which property do you need to access?

About the mac address. I don't know how ABWifi is implemented however the values in the PeersDiscovered event come directly from the underlying layer.

Android Tutorial Android Wifi-Direct Tutorial

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