Yea, trying to communicate between any two Androids, or any devices
for that matter, using their IP address is probably going to be next
to impossible, in the general case.
It would work OK inside an intranet where IP addresses are less
volatile (like the way controllers communicate with robots over a
local wireless LAN). Even then the devices are configured to have
predetermined, unchanging IP addresses.
Like Bob Kerns says you may way to consider using a server as
intermediary, much the same way that instant messaging works. A
reasonably dependable connection can be established between a server
and the Android and then the server can pass messages between the two.
If the Androids are in close proximity, like in the same small room,
take a look at Bluetooth for establishing a connection. That works
really well in such cases.
BTW, you can determine an Android's IP address like this:
public String getLocalIpAddress() {
try {
for (Enumeration<NetworkInterface> en =
NetworkInterface.getNetworkInterfaces(); en.hasMoreElements();) {
NetworkInterface intf = en.nextElement();
for (Enumeration<InetAddress> enumIpAddr =
intf.getInetAddresses(); enumIpAddr.hasMoreElements();) {
InetAddress inetAddress = enumIpAddr.nextElement();
if (!inetAddress.isLoopbackAddress()) {
return inetAddress.getHostAddress().toString();
}
}
}
} catch (SocketException ex) {
}
return null;
}
But it is mostly useless as it is usually known only to the nearest
DHCP server and not outside that sphere.
On Jan 28, 7:44 am, Bob Kerns <[email protected]> wrote:
> The IP addresses will be whatever the DHCP server on that subnet says
> they should be. Often, the DHCP server role will be handled by your
> router to the internet, but in a corporate environment, things may be
> more complicated.
>
> When a device connects to an IP network, it usually broadcasts "who am
> I?", and a DHCP server then tells it basic stuff like it's IP address.
> This can be a pre-allocated address assigned to that device, or it can
> be allocated dynamically from a pool of addresses.
>
> I would guess you don't want to require pre-assignment, because,
> typically, users would not be able to do so.
>
> So how do the devices discover each other's IP addresses?
>
> Well, there are a lot of options there. You can have each user type in
> the IP address. You can register the device dynamically under a DNS
> server, and have them type in the DNS name. You can use a service
> discovery protocol (like Apple's Bonjour service). You can roll your
> own using broadcast or multicast messages. You can register each
> device on a server -- and then even talk to each other THROUGH the
> server. This last has the great advantage that it allows two devices
> on incompatible networks to communicate. (I presume the disadvantages
> are obvious).
>
> About the only thing I can say for sure is -- you're going to need to
> know more about networking than you do today. It's learnable, and
> there are resources out there to help. Most of what you need to know
> is information that is not specific to the Android platform, so there
> will be a wide array of sources of information. Google searches are
> you friend.
>
> You can probably accomplish everything you're trying to do entirely
> with the classes in the java.net package. So you can develop your
> approach in any connected Java environment.
>
> On Jan 28, 1:56 am, Tony <[email protected]> wrote:
>
> > Hello ,all!
>
> > If I connect two android pwer real-devices to a LAN through wifi,
> > then what are their IP adress???
>
> > How can then find each other by IP address???
>
> > are their IP address 192.168.0.* ??
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