We are getting in the design phase of using MvvmCross for our application platform and we are trying to figure out if we can use the MvvmCross Plugin to broadcast messages between multiple MvvmCross applications? These applications will be running on the same machine in parallel, and on an internal network.
I did consider using RabbitMQ for this but found out that you cannot add RabbitMQ to a Portable Class Library Project. So that's out of the question.
I watched this video : https://www.youtube.com/watch?v=HQdvrWWzkIk and the speaker says the Messenger can be used within an application, but I would like to know if it can enable communication between different applications.
Any help would be greatly appreciated.
My guess is that it probably creates an instance and uses that for communication, making it less ideal (if possible) for across applications.
You should be able to create a program that listens to a port and redirects accordingly, creating the same functionality though.
What I ended up doing was creating a Windows Service Hosted, WCF service (NET TCP) which enabled me to do cross process communication. Then when a process received a message via WCF, it relayed the message internally using the MVVMCross Messenger.
Seems to work pretty well so far, although it's only been used with 3 processes. So not sure about the scalability of this solution.
Related
I am working on a project requiring communication between the Presentation layer (MVVM based client) and the Business layer. The application is to be installed on a single machine, and as such could have been executed using a .net remoting based approach. However, I have been suggested to use WCF since .net remoting is deprecated and WCF is the way to go.
So I implemented WCF Service as a WCF library project. I added a service reference (using visual studio tool by discovering services in the solution), which was successfully added on the client side. All works well, since during debug session visual studio launches the service library and the client can connect to it successfully.
Now Since the client and service host will be installed on same machine, I was thinking of using named pipes transport and self hosting for the WCF service. Here is where this gets very confusing to me:-
Since the MVVM client is the "main" app (since it is the application frontend), the client will be launched first. I am unable to come up with a solution to launch the service host "on-demand" when the client needs the same.
What are the solution I can use to do what I require for 1? I am not sure of using a continuous service through windows service for something that will be required "on-demand".
Please suggest clean approach to implement a way to launch "on-demand" service.
Thanks in advance.
I'm not quite following you here. MVVM is cake and really doesn't have anything to do with your problem. Using a servicebased architecture is a must today, I just want to smack every old guy/gal sticking to direct SQL on the client side, and don't see the dangers with that.
Well anyhow, you may solve this different ways. WCF is BIG, to big in my opinion. One way to use it, common on small applications like apps(WP8.1, 8.1 apps++), is just to connect, call the method you need and the close the connection. Case solved, given that I understand your needs. The otherway is to keep the session alive for each service... (ugh, loadbalancing etc).
I've been working on large LOB applications the last 4 years my self, what I can tell, is that if I were in charge, I would have done it very differently. For once I would used JSON endpoints with SSL over HTTP, and the json.net serializer. The datacontract serializer which is the default in WCF, is not good news at all. JSON allows easy communication with JavaScript based applications, and the serializer doesn't break like porcelain as the datacontract serializer does. Address/baseaddress may be stored in your config file, so it may be changed upon deployment(you probably have many servers, for different environments).
This is a really old post covering the subject(supporting SOAP aside JSON); REST / SOAP endpoints for a WCF service
Don't be stupid and just call your services directly now! Use the interface(Wrap if necessary) and feed it to your viewmodels for proper TDD! It will also allow you to completely replace WCF with another form of communication.
There also are alternatives to WCF.
IIS? Hosting WCF in IIS rather than a proper service? No way, flush that idea down the waterloo ;) (internal joke)
EDIT:
BTW: Your service must ofc already be running for your client to connect to it! Or nothing will be listening to your configured port. If you are selfhosting, you can use parameters to start in debug mode, that is start your service like a regular application you may debug. In Program.cs;
if (args.Length > 0 && String.Equals(args[0],"debugmode", StringComparison.OrdinalIgnoreCase)
{
Service1.Create(); // Debugging!
}
else
{
// Hosting
service = new Service1{ServiceName="YourService"};
ServiceBase.Run(new ServiceBase[] {service};);
}
Hope it helps,
Cheers,
Stian
I have a WPF application, that I want to port to Linux/Mac. The most logic way seems to split the application in two parts: client and server, and use Silverlight for the client UI, and run the server-part (as an invisible console-app) in Mono.
But what's the best way to let those two parts communicate? Silverlight 4 supports COM interop, but I cant use that because it will fail in Moonlight. So I was thinking about socket-connection to localhost, and use JSON or something similar. Or is there a better way which doesn't require me to write dozens of wrappers for all the function contained in the server-dll? Because communication will be between Mono<>Moonlight, maybe i can use something similar as COM interop that is cross-platform?
maybe you can consider to use Eneter Messaging Framework.
It allows to implement the communication between Silverlight and standalone application based on Tcp. The low level communication is hiden and the framework is very easy to use.
You can see the following example:
http://eneter.blogspot.com/2010/07/silverlight-interprocess-communicatin.html
You're on the right track.
You should create a web server application and the Silverlight app would communicate with it over http://localhost via REST or SOAP.
Joshua - I'm a bit confused (and I don't mean that in a negative way). If the app runs on the users machine then isn't there's no "server" to connect with?
What's the nature of the server-side components? - what do they do? Can't you just run the whole thing from within SilverLight?
SilverLight is providing the runtime host for .Net, in that sense it can contain your whole app - which can still be layered like a "conventional" web-based solution, so you can still have separate assembilies for Business Logic, etc.
I need to grab information between two instances of my WPF app (the contents of a public collection, to be precise). Any help?
You'll need to use some form of Interprocess Communication.
Since you're using WPF, and hence .NET, I'd recommend using Windows Communication Foundation. If these instances are running on the same system, using pipes via WCF is a great option.
Do you mean between two processes or app domains? I'd look up AppDomain and see if that works for your situation. If you need to communicate between two processes, I'd use named pipes through WCF.
I am trying to work on a home project so I can get some practice working on WPF & WCF applications. Can anyone give out suggestions on a sample WPF and or WCF applications that I can develop?
A project I was thinking about was to help regulate my teenage son's internet usage.
Windows has a UI-based tool to control logon times. A WPF front-end would be nice to duplicate or improve on that tool, but use it to set network usage times. This way, kids could do school work (not prohibited from logging on their computer) but not be distracted by facebook.
The WCF portion would be a WCF service on your computer and WCF client on the kids' computers. The kids' computers would periodically check for restriction updates. If network access is current OFF, then the client (on the kids' computer) would turn off the network adapters (both ethernet and Wifi), turn them on every few minutes to check for updates, then turn them off again.
Just define a data contract for whatever structure/class you want to represent usage, and the service would have an operation contract with a single call, like:
[ServiceContract]
interface INetworkControl
{
[OperationContract]
NetworkRestriction GetNetworkRestriction();
}
Maybe it would need more; that would be up to you (i.e., pass the computer name as a parameter, or perhaps logged on user if you wanted to control by user, who knows).
Maybe a peer to peer program ?
Not sure...I learned the 2 technologies by writing a facebook API based on WCF and writing a WPF frontend to browse the albums of my friends. My reasoning was that if WCF can do form-encoded POSTs with bare XML responses then it should be up for a lot of things.
I have bought an excellent program/tutorial here :
http://www.dofactory.com/Framework/Framework.aspx
I includes a program where WCF services are consumed by WPF (as well as by Windows Forms and a ASP.NET website).
It's about design patterns basically, but using services as datasupplier is a design pattern too of course.
(for the record : I really am not advertising for this company :-))
I think this might give you plenty ideas for your own programs, and if the aim is getting to know both technologies, it would be an excellent choice.
I am creating a Silverlight 2 user interface to a remote instrument. There are two concurrent users at different sites interacting with the instrument (operator at the instrument and remote scientist) and any number of observer users not interacting with it, just watching. However, whenever one of the two active users changes something these changes must be immediately reflected in the UIs of all users, e.g. panning or zooming an image or annotating or selecting part of an image, adding items to a collection displayed in a listbox. Within the client I use observable collections which easily reflect changes made by that user, but it is harder seeing changes made by another user. I can poll for changes from each client but something like push notifications would be better. I have extensively Googled for examples but not found anything which is quite what I need. There are all sorts of security issues with Silverlight interacting with WCF services which mean many potential examples just don't work. I have essentially run out of time on this project and need help fast. Does anyone have any suggestion of a suitable simple example which illustrates how to do this? I am an experienced developer but have had to teach myself Silverlight and WCF services and there is noone in my area who knows anything about these. Even tho' I have done a fair amount of ASP.NET work I am not a web/Javascript guru. Thanks.
Push notification is supported in Silverlight 2 using the new WCF PollingDuplexHttpBinding support. There are two assemblies installed with the Silverlight SDK (one for Silverlight app one for WCF server).
I have a few blog posts and a full sample application that demonstrate how to 'push' Stock updates from a Console Application server that self-hosts a WCF service to connected clients. It also shows how each client can add notes against a Stock and have those notes synchronized (pushed from server) to all other connected clients.
The latest version of the sample (Part 4) shows how to synchronize pushed updates between both Silverlight and WPF clients using two server endpoints as follows:
using System;
using System.ServiceModel;
using System.ServiceModel.Description;
namespace StockServer
{
public class StockServiceHost : ServiceHost
{
public StockServiceHost(object singletonInstance, params Uri[] baseAddresses)
: base(singletonInstance, baseAddresses)
{
}
public StockServiceHost(Type serviceType, params Uri[] baseAddresses)
: base(serviceType, baseAddresses)
{
}
protected override void InitializeRuntime()
{
this.AddServiceEndpoint(
typeof(IPolicyProvider),
new WebHttpBinding(),
new Uri("http://localhost:10201/")).Behaviors.Add(new WebHttpBehavior());
this.AddServiceEndpoint(
typeof(IStockService),
new PollingDuplexHttpBinding(),
new Uri("http://localhost:10201/SilverlightStockService"));
this.AddServiceEndpoint(
typeof(IStockService),
new WSDualHttpBinding(WSDualHttpSecurityMode.None),
new Uri("http://localhost:10201/WpfStockService"));
base.InitializeRuntime();
}
}
}
WPF clients connect to the WSDualHttpBinding endpoint and Silverlight clients connect to the PollingDuplexHttpBinding endpoint of the same WCF service. The app also shows how to handle the Silverlight client access policy requirements.
Clients (Silverlight or WPF) can add notes against a Stock in their UI and these notes propagate back to the server to be pushed to all other clients. This demonstrates communication in either direction and hopefully performs all of the necessary communication required for your app.
You can see a screenshot of the demo application running here.
Not that am pushing Flex in fan boy fashion, but matter of factly this is the kind of architecture we build into all our Flex-based applications routinely. Here is what we do on Flex - no doubt it could be suitably translated to Silverlight:
We take three ingredients and integrate them together to accomplish this capability:
Comet pattern (an HTTP compatible way to do server push notifications - look on Wikipedia for more info)
JMS messaging topics (publish/subscriber queues)
The Adobe BlazeDS servlet
The latter item implements the Comet pattern, supports AMF object marshaling (Adobe's binary serialization format for ActionScript3 objects), and bridges to a JMS queue or topic. When bridging to a topic, then multiple Flex clients running in a browser can be proxied in as subscribers to a JMS topic. So if any client publishes a message (or the server-side code publishes into the topic), all client subscribers will have the message pushed to them via BlazeDS and the Comet Pattern implementation.
Effectively you need to locate or write a component that accomplishes what BlazeDS does. You might also need to implement some client code that interacts with the Comet pattern of this server-side component.
Does WCF support the Comet Pattern and bi-directional messaging? Especially where complies to HTTP and port 80 or port 443 for SSL. Looks like you've already looked into that and not found anything for bi-directional messaging. So you may need to roll your sleeves up and do some coding.
Some things to note about doing server push to a web app:
BlazeDS supports two primary modes of implementing the Comet pattern (there's actually a 3rd polling option but am ignoring it):
long-polling
HTTP streaming
The long-polling one you should find to be more universally supportable to most web browsers. So you might streamline to just supporting that initially. Or you could spend the time to make your client code try HTTP streaming first and switch to long-polling if necessary.
As to a message broker that can provide publish/suscribe capatibility, you might consider using ActiveMQ JMS. It is open source and free with active community support (you can buy support too). Plus you can use NMS to integrate as a .NET client.
Having a message broker sitting in the middle-tier is actually important because it will be a place for messages to be placed safely. If your clients are doing long-polling, you wouldn't want them to miss any new message during an interval when they're not actually connected.
Another thing to consider in high traffic volume scenarios (hundreds or thousands of clients, such as a web site on the Internet), you need to have an approach to the Comet Pattern that is scalable.
In the Flex/Java world, the BlazeDS servlet (which is open source) has been modified to work with asynchronous model. In Java a socket listener can be built to use NIO channels and Java Concurrency Executor thread pools. The Tomcat web server has a NIO listener and support for asynchronous Servlet 3.0 events. BlazeDS in particular has been modified, though, to work with the Jetty web server. The bottom line is that the scalability of this asynchronous approach means a single physical web server can be enhanced to support up to around 20,000 concurrent Comet-style client connections.
It's been a while since I've done serious .NET programming but used to the io capabilities were much like Java 1.1 except with an asynchronous result handler capability. This, though, is not the same thing as creating asynchronous socket listeners via Java NIO channels. A NIO channel implementation can support hundreds to thousands of socket connections with a relatively small thread pool. But C# and .NET has gone through two or three significant revs - perhaps there have been new io capabilities added that are comparable to NIO channels.
I just wanted to clarify that the PollingDuplexHttpBinding doesn't implement 'true' push notifications, as reveals its name (polling). From the msdn documentation:
When configured with this binding, the Silverlight client periodically polls the service on the network layer, and checks for any new messages that the service wants to send on the callback channel. The service queues all messages sent on the client callback channel and delivers them to the client when the client polls the service.
However it is more efficient than the traditional way of polling a web service, since after each poll, the server will keep the channel open for a certain time (say 1 minute), and if a message arrives in that time it will directly 'push' the message to the client. The client has to repeatedly renew its connection, it so to say polls the service.
If you want to implement real push notifications with silverlight I believe you need to work with sockets, and I recommend reading some of Dan Wahlin's blog posts on the subject.
Alternatively,
if you want a native silverlight API with no proxies, bridges or webservers involved you could use Nirvana from my-Channels as your messaging middleware. Check out Nirvana from my-Channels and their showcase site. (sorry i am a new user and cant submit links):
Alex
EDIT: it's actually working fine. I got badly bitten by the "hidden variable" in a closure :(
I used the PollingDuplex for SL2 and I think that it's not ready for production yet.
My main issue is the fact that it doesn't discriminate on the clients on the same machine. If I run 2 clients then one of them won't be able to poll the server anymore and will die of timeout. There is a SessionId that is different for the 2 clients but it's just ignored on the client side.
Likewise, if I kill a client and then create a new one afterwards then the new client will get the push updates from the previous client for a while.
Did anyone encounter the same issues or are they fixed in SL3?
Actually I ran some more demo codes and realised that for some reason you have to specify the InstanceContextMode and InstanceMode so that the service is session based and not a singleton (as far as I can tell). There are clear performance issues in the simple demo code that I pulled.
It is quite unfortunate that this behaviour wasn't documented.
My organization found the Silverlight 2.0/WCF push implementation to be a little "not ready for prime time", at least for what we were planning to use it for.
We ended up going with XMPP/Jabber, because it is a more well formed beast, and you can implement it fairly easily in Silverlight, by just getting some resources off the internet.
I do believe that Silverlight 3.0 will implement a newer/more well formed push implementation, from what I can tell from publicly available information.
The PollingDuplexHttpBinding is probably the most elegant way to do it.
One possilby less involved alternative is to use a TCP socket from your Silverlight client. Whenever one of the Silverlight clients needs to have an update pushed you can send it a TCP message which contains the name of the WCF service it needs to call or some other light weight piece of information.
I use this approach for an application and it works well.
One much simpler and more powerful solution at the site http://www.udaparts.com/document/Tutorial/slpush.htm