I have a project and am right now at a point, where it's growing complexity forces me to think about it's structure. To explain it in a few sentences:
I have a main application as UI. It allows the user to run different tests and should display status updates and results.
I have a whole bunch of classes containing different tests on some hardware. All those classes implement an iTest interface to ensure compatibility.
Where I am right now: I want to have status updates (which I don't get right now). I need some kind of StatusUpdate-Event fired in the Test-Classes and receive those events in my UI. I'm new to delegates and event handlers so I have no clue which way is the best to choose for this. Following the answer from here "How to add an event to a class" means I'd have to add a event handler each time I instantiate one of my test classes. That would generate a whole load of redundant code that I think is unnecessary.
I'd like to have one function in my UI named sth. like "StatusUpdateEventHandler(string textToDisplay)". It should not matter, which Test-Class invokes this event.
Can anyone give me some direction where to go at? Thank's a lot :)
I'll use a base class that have common properties/methods/events to report progress back to the UI. Quickly, this is how I would approach the problem:
Create an event Handler to report progress:
public delegate void StatusChangedEventHandler(object sender, StatusChangedEventArgs e);
Create an abstract base class:
public abstract class TestBase:ITest
{
// An event that clients can use to be notified whenever the
// elements of the list change.
public event StatusChangedEventHandler StatusChanged;
protected virtual void OnStatusChanged(StatusChangedEventArgs e)
{
if (StatusChanged != null)
StatusChanged(this, e);
}
protected virtual void ReportProgress (int percentage, string step)
{
OnStatusChanged(new StatusChangedEventArgs()
{
Percentage = percentage,
Step = step
});
}
public abstract void Execute();
}
Create a EventArgs that will be used to get data from the event in your UI:
public class StatusChangedEventArgs:EventArgs
{
public int Percentage { get; set; }
public string Step { get; set; }
}
Then make sure that your tests use the base test class:
public class SimpleTest : TestBase
{
public override void Execute()
{
ReportProgress(10, "STEP 1");
ReportProgress(25, "STEP 2");
ReportProgress(55, "STEP 3");
ReportProgress(70, "STEP 4");
ReportProgress(100, "STEP 5");
}
}
Then hook up the event to your UI, here's my implementation in a console application:
class Program
{
static void Main(string[] args)
{
SimpleTest simpleTest = new SimpleTest();
simpleTest.StatusChanged += SimpleTest_StatusChanged;
simpleTest.Execute();
Console.ReadLine();
}
private static void SimpleTest_StatusChanged(object sender, StatusChangedEventArgs e)
{
Console.WriteLine($"{e.Percentage} - {e.Step}");
}
}
I couldn't say you provided a lot of info to suggest a really helpful response. :-) It seems to me you look for something like generic events, see example within the article. You'd subscribe to the events which are fired by the test units, so the relevant string is passed along with each particular event. Besides, you could consider some class hierarchy to support your test units.
Hope it brings you some fresh thoughts to find the direction.
Ok guys I'm totally new to stackoverflow, let me know if I stuff something up.
I am making a class library for sockets and then using the class library to make a server. The issue I've run into is this:
In the class library I have a class called sockets that has event handlers (you know like connection made, closed so on) and in the server I'm making, I have a class named player which inherits from sockets.
The problem pretty much comes down to this.
I use the OnConnectionMade event handler to create my player, but because I cant do instanceOfInheritedClass = intanceOfBaseClass, even when I make use of use of the event handlers, the event handlers wont trigger because instanceOfInheritedClass isn't pointing to intanceOfBaseClass event, if I pass through the parameters.
void hostManager_OnConnectionMade(object source, ConnectionArgs e)
{
Player socket = new Player(e.GetSocket());
socket.OnDataRecivedPostConvert += Socket_OnDataRecivedPostConvertLogin;
}
public Player(DDSocket socket)
{
this.Host = socket.Host;
this.Socket = socket.Socket;
//this.OnConnectionClosed += socket.OnConnectionClosed;
//this.OnDataRecivedPostConvert += socket.OnDataRecivedPostConvert;
//this.OnDataRecivedPostConvertHost += socket.OnDataRecivedPostConvertHost;
}
One of the solutions I came up with was that instead of inheriting, I can just make it a intanceOfBaseClass parameter in the player class. But that will prevent me from making proper use of object source from my event handlers which will mean I'll need to use linq or something to find the player from the socket or something like that.
The other thing I thought about doing was somehow passing the event handlers over, which you can see I tried, but don't know how to do.
Now after hours of looking it up I'm stuck. Any help is greatly appreciated
and any answer that solves this issue is fine. I'm not picky with how its solved.
Despite that your Player class is inherited from DDSocket, but in this scenario, it acts as the wrapper class of DBSocket, so there is one hack to achieve that, I think you have to do some further steps:
class DDSocket
{
public event Action OnConnectionClosed;
public void Raise()
{
if (OnConnectionClosed != null)
{
OnConnectionClosed();
}
}
}
class Player :DDSocket
{
// make new event look as the same base class
public new event Action OnConnectionClosed;
public Player(DDSocket socket)
{
socket.OnConnectionClosed += Socket_OnConnectionClosed;
}
private void Socket_OnConnectionClosed()
{
if (OnConnectionClosed != null)
{
OnConnectionClosed();
}
}
}
// test those 2 classes
static void Main()
{
DDSocket d = new DDSocket();
Player pl = new Player(d);
pl.OnConnectionClosed += () => MessageBox.Show("test");
d.Raise();
}
I'm having a bit of a problem with implementing an event architecture in C#. The basic layout is like this:
We have a network-layer(dll) that communicates with a server. This layer has made several interfaces for events of changes within the database. A database-field changes and the dll calls my implementation of the appropriate interface. I have a GUI, and within it's main method a data-object, which stores lists of temporary data I display until something gets changed by my user, in which case I'll send the changes to the database.
The problem is now that I can't implement an event-handler within the network-layer, or my implementation of it's interfaces, because my data-object(which should get the results of the events) only exists within my GUI, and it's main method, and as such is not known to the appropriate objects.
I'll make an example as pseudo-code:
namespace ClientConnection
{
public class DataListener : IDataListener
{
public delegate void SomethingReceivedHandler(object sender, SomethingData packet);
public event SomethingReceivedHandler somethingRecievedHandler;
public void SomethingReceived(SomethingData packet)
{
if (SomethingRecievedHandler != null)
{
SomethingRecievedHandler(this, packet);
}
}
Is my current implementation of the interface. The Layer has something akin to:
private void ProcessPacket(SomethingData packet)
{
if (packet == null)
return;
try
{
if (packet is SomethingData)
DataListener.SomethingReceived(packet as SomethingData);
//snip
And my main-method is:
public partial class Main : FormMain
{
Data ClientData; //Contains all temporary data within the GUI
public frmMain()
{
ClientData = new Data();
DataListener dataListener = newDataListener();
InitializeComponent();
}
And if the event fires I want to do something like:
ClientData.SomeList.Add(packet)
depending on the context.
The problem is now that I can't implement an event-handler within the network-layer, or my implementation of it's interfaces, because my data-object(which should get the results of the events) only exists within my GUI, and it's main method, and as such is not known to the appropriate objects.
Not sure I see the problem. The publisher of the event doesn't need to know anything about the subscriber of the event - that's what makes them useful.
Based on your pseudo-code, it should be as simple as:
public partial class Main : FormMain
{
Data ClientData; //Contains all temporary data within the GUI
public frmMain()
{
ClientData = new Data();
DataListener dataListener = new DataListener();
// Add an event handler
dataListener.somethingReceivedHandler +=
(object sender, SomethingData packet)
{
if (someContext) ClientData.SomeList.Add(packet);
};
InitializeComponent();
}
You probably want to elevate dataListener to a field (instead of a local) so that it stays alive outside of the ctor (and you can unsubscribe when your form closes).
I am making a personal WinForms app. In my scenario say I have a C# Form1. Form1 is constantly getting live Exchange data from the Internet. Now I click a button on Form1 and Form2 opens. Now I want some values from Form1 on Form2.
I have a timer on Form2 which can collect data from Form1 but how?
I had tried to use properties but not able to do that as it updates only once as when we initialize Form2.
Any solution?
Also, how can I pass a single instance of a class to both forms, if they are not being created at the same time?
I. Solution: Use a Common Data Source
Method 1: Data Source with Events
Well, if it were me, I would probably not be trying to directly get the data from Form1. Instead, I would set up a common datasource, and then you would even be able to eliminate the timer on Form2 and drive it by when the data comes in if you like. (Or you can leave it and just pull from the datasource as your desired intervals.)
It would be something like this:
Data Source class
public class ExchangeCommonDataSource
{
public event EventHandler NewDataReceived;
public void FireNewDataReceieved()
{
if (NewDataReceived != null)
NewDataReceived();
}
private string mySomeData1 = "";
public string SomeData1
{
get
{
return SomeData1;
}
set
{
SomeData1 = value;
FireNewDataReceieved();
}
}
// properties for any other data
}
Then, when you are opening your forms, you'll just create an instance of ExchangeCommonDataSource, and pass it to both of the forms. In the form that is receiving the data you'll want to create an event handler function, and wherever you pass it the data source, you'll hook up that event.
example: receiving class code
public void HandleDataReceived(object sender, EventArgs e)
{
// display the data
DoSomethingWith(mySource.SomeData1);
// etc...
}
private ExchangeCommonDataSource mySource;
public void SetDataSource(ExchangeCommonDataSource newSource)
{
mySource = newSource;
mySource.NewDataRecieved += new EventHandler(HandleDataReceived);
}
Then, in your first form, you just set the properties you want. You can actually have notifications that specified the actual data to load, either through separate event handlers, or by creating your own derived EventArgs and then using EventHandler<ExchangeCommonEventArgs> instead of a regular event handler.
example: main form data accessor
public void GetDataFromExchange()
{
mySource.SomeData1 = GetSomeData1FromExchange();
}
Also, this way you're not limited to having just those two forms communicate; if you decide to split it up with different forms, you could have each of them have a copy of the data source and each of them could handle the event or new events you define, and you're not tied to a model where you're expecting to communicate directly between each other. This would also allow, for instance, creating a separate class which writes some log data to disk, or whatever else you can imagine, without making significant changes to any of your existing stuff.
II. Extensibility for External Updates
The Dispatcher Base Class
So, what if you want to update to eventually send to another application or another machine even?
Well, this is actually very well accounted for since you've not got any dependencies on the forms left. So, say you wanted to support three methods: the initial, form to form method; sending via a named pipe to another app on the same machine; and TCP/IP to another machine entirely. All you would need to do is to define a class that acts as a dispatcher, hook it up as a receiver, and then you can hook up that object to take the events coming from the form and put the data wherever you want.
It should be fairly straightforward to define an abstract class or interface to do this, and then simply derive a class for any mode you want to support:
example: a notional abstract Dispatcher class
public class ExchangeDataDispatcher :
IDisposable
{
public ExchangeDataDispatcher(ExchangeCommonDataSource parDataSource)
{
myDataSource = parDataSource;
myDataSource.HandleDataReceived +=
new EventHandler(HandleDataReceived);
DispatcherInitialization();
}
private ExchangeCommonDataSource myDataSource;
private void HandleDataReceived(object sender, e EventArgs)
{
// here you could record statistics or whatever about the data
DispatcherHandleDataReceived(EventArgs);
}
protected abstract void DispatcherHandleDataReceived(e EventArgs);
protected abstract void DispatcherShutdown();
// significantly ripped from Microsoft's page on IDisposable
private bool disposed = false;
protected virtual void Dispose(bool disposing)
{
// Check to see if Dispose has already been called.
if(!this.disposed)
{
// If disposing equals true, dispose all managed
// and unmanaged resources.
if(disposing)
{
// call a function which can be overridden in derived
// classes
DispatcherShutdown();
}
// Note disposing has been done.
disposed = true;
}
}
}
see the Microsoft page on IDisposable for some great example code and more information on IDisposable...
Deriving Dispatchers for Other Communication Methods
There's no way to make the form itself derive from this class, but there's no real need since you can just hook up as before. But, as quick example (just notional, not actually implementing the protocols, and you really should really consider the best way to implement these types of things, but I wanted to give you a fairly comprehensive example of what it takes, it's not as simple as the really really naive versions tend to be. )
example: (very) notional Pipe-based Dispatcher
// add these to your using statments
using System.IO.Pipes;
using System.Threading;
// NOTE: take all the async stuff with a grain of salt; this should give you a
// basic idea but there's no way I've gotten it right without actually testing
// and debugging everything. See the link
// http://stackoverflow.com/questions/6710444/named-pipes-server-read-timeout
// for some information on why it has to be done this way: basically timeout
// is not supported for named pipe server streams.
public class ExchangeDataLocalMachineDispatcher :
ExchangeDataDispatcher
{
// see http://www.switchonthecode.com/tutorials/dotnet-35-adds-named-pipes-support
// for some info on named pipes in .NET
public ExchangeDataLocalMachineDispatcher(
ExchangeCommonDataSource parDataSource,
NamedPipeServerStream ServerPipe
) :
base(parDataSource)
{
myPipe = ServerPipe;
// do any extra initialization, etc. here, negotiation for instance
StartPipeThread();
}
private NamedPipeServerStream myPipe;
private ExchangeCommonDataSource myDataSource;
// assuming you have PipeMessage defined and that your handler
// fills them in.
private List<PipeMessage> myOutgoingMessages =
new List<PipeMessage>();
private Thread myPipeThread;
private bool EndPipeListener = false;
private AutoResetEvent myWaitEvent = null;
private AutoResetEvent myDataReadyToGoEvent = null;
// set this to something reasonable for the response timeout
private int WaitTimeout = 10000;
// example: at least every minute there should be data to send
private int WaitForDataToSendTimeout = 60000;
private void StartPipeThread()
{
IAsyncResult LastResult = null;
Action<IAsyncResult> WaitForResult =
(a) =>
{
LastResult = a;
myWaitEvent.Set();
}
myPipeThread = new System.Threading.ThreadStart(
() =>
{
try
{
myWaitEvent = new AutoResetEvent(false);
myPipe.BeginWaitForConnection(
WaitForResult, null
);
bool TimedOut = !myWaitEvent.WaitOne(WaitTimeout);
if (TimedOut || !LastResult.IsCompleted)
throw new Exception("Error: pipe operation error.");
while (!EndPipeListener)
{
byte[] Response = myPipe.BeginRead(
WaitForResult, null
);
myWaitEvent.WaitOne(WaitTimeout);
if (TimedOut || !LastResult.IsCompleted)
throw new Exception("Error: pipe operation error.");
// another assumed function to handle ACKs and such
HandleResponse(Response);
myWaitEvent.Set();
// now wait for data and send
bool TimedOut =
myDataReadyToGoEvent.WaitOne(WaitForDataToSendTimeout);
if (TimedOut || !LastResult.IsCompleted)
throw new Exception("Error: no data to send.");
// an assumed function that will pull the messages out of
// the outgoing message list and send them via the pipe
SendOutgoingMessages();
myDataReadyToGoEvent.Set();
}
myWaitEvent.Set();
}
finally
{
// here you can clean up any resources, for instance you need
// to dispose the wait events, you can leave the pipe for the
// DispatcherShutdown method to fire in case something else
// wants to handle the error and try again... this is all
// fairly naive and should be thought through but I wanted
// to give you some tools you can use.
// can't remember if you're supposed to use .Close
// .Dispose or both off the top of my head; I think it's
// one or the other.
myWaitEvent.Dispose();
myDataReady.Dispose();
myWaitEvent = null;
myDataReady = null;
}
}
);
}
protected PipeMessage[] ConstructEventMessage(e EventArgs)
{
// actually we're not using the event args here but I left it
// as a placeholder for if were using the derived ones.
return
PipeMessage.CreateMessagesFromData(
myDataSource.GetMessageData()
);
}
protected override void DispatcherHandleDataReceived(e EventArgs)
{
// create a packet to send out; assuming that the
// ConstructEventMessage method is defined
myOutgoingMessages.Add(ConstructEventMessage(e));
}
protected override void DispatcherShutdown()
{
// this is called from the base class in the Dispose() method
// you can destroy any remaining resources here
if (myWaitEvent != null)
{
myWaitEvent.Dispose();
}
// etc. and
myPipe.Dispose();
}
// you could theoretically override this method too: if you do, be
// sure to call base.Dispose(disposing) so that the base class can
// clean up if resources are there to be disposed.
// protected virtual void Dispose(bool disposing)
// {
// // do stuff
// base.Dispose(disposing);
// }
}
Phew. Note that I'm very unhappy currently with the length of the StartPipeThread function, and I would definitely be refactoring that.
So, you could also implement this for TCP/IP sockets, or whatever protocol you can imagine, and it's all handled without having to continually modify the classes from the first section.
My apologies for the quality of any of the code there; I am open to suggestion/correction/flaming about it, and I'll do my best to make corrections if you just let me know. :P
III. Putting the Data Where it's Needed
After you have this set up, you'll need to pass the same data to whatever forms are using it. If you're not creating both your forms at the same time, then you'll need some way to get each destination a reference to the same data source. (Note: the numbering of the options is in no way intended to imply these are your only choices!)
Here are a few options for doing so:
Option 1: via Property on your main Form
This method is appropriate if your main form is responsible for creating each of the child forms, for instance, through menu items. You simply create a member variable to hold the data, and wherever you create the data, store a reference to it in that member. If you have multiple instances of the source, you can store them e.g. in a dictionary that allows you to look up the one you need.
example: code for main Form
private ExchangeCommonDataSource myData { get; set; }
// you can also store in something that lets you identify multiple
// possible data sources; in this case, you could use, say, email address
// as a lookup: myData["mickey#example.com"];
//private Dictionary<string, ExchangeCommonDataSource> myData =
// new Dictionary<string, ExchangeCommonDataSource>();
public frmMyMainForm()
{
InitializeComponent();
// ... other initialization for the main form ...
// create the data here and save it in a private member on your
// form for later; this doesn't have to be in the constructor,
// just make sure you save a reference to the source when you
// do create your first form that uses the source.
myData = new ExchangeCommonDataSource();
}
// then, in the methods that actually create your form
// e.g. if creating from a menu item, the handlers
public void FirstFormCreatorMethod()
{
frmFirstForm = new frmFirstForm(myData);
frmFirstForm.MdiParent = this;
frmFirstForm.Show();
}
public void SecondFormCreatorMethod()
{
frmSecondForm = new frmSecondForm(myData);
frmSecondForm.MdiParent = this;
frmSecondForm.Show();
}
Option II: static Properties on your Data Source
This option can be used if the forms are being created externally from the main form, in which case you will not have access to its methods. The idea behind this method is that you want an easy way to find whatever item you need, independent of the main form itself, and by providing a static method, additional data consumers can find the sources on their own using properties accessible with access only to the class declaration and then some sort of key if there can be multiple sources.
example: ExchangeCommonDataSource.cs
// a dummy source class; this is just the parts that were relevant
// to this particular discussion.
public partial class ExchangeCommonDataSource
{
public string Username { get; set; }
public string OptionalString { get; set; }
public int MailboxNumber { get; set; }
public Guid SourceGuid { get; set; }
public long BigNumber { get; set; }
// these static members provide the functionality necessary to look
// retrieve an existing source just through the class interface
// this holds the lookup of Guid -> Source for later retreival
static Dictionary<Guid, ExchangeCommonDataSource> allSources =
new Dictionary<Guid,ExchangeCommonDataSource>();
// this factory method looks up whether the source with the passed
// Guid already exists; if it does, it returns that, otherwise it
// creates the data source and adds it to the lookup table
public static ExchangeCommonDataSource GetConnection(
Guid parSourceGuid, string parUsername, long parBigNumber
)
{
// there are many issues involved with thread safety, I do not
// guarantee that I got it right here, it's to show the idea. :)
// here I'm just providing some thread safety; by placing a lock
// around the sources to prevent two separate calls to a factory
// method from each creating a source with the same Guid.
lock (allSources)
{
ExchangeCommonDataSource RetVal;
allSources.TryGetValue(parSourceGuid, out RetVal);
if (RetVal == null)
{
// using member initializer, you can do this to limit the
// number of constructors; here we only need the one
RetVal = new ExchangeCommonDataSource(parSourceGuid) {
Username = parUsername, BigNumber = parBigNumber
};
allSources.Add(parSourceGuid, RetVal);
}
return RetVal;
}
}
// this function is actually extraneous since the GetConnection
// method will either create a new or return an existing source.
// if you had need to throw an exception if GetConnection was
// called on for existing source, you could use this to retrieve
public static
ExchangeCommonDataSource LookupDatasource(Guid parSourceGuid)
{
// again locking the sources lookup for thread-safety. the
// rules: 1. don't provide external access to allSources
// 2. everywhere you use allSources in the class,
// place a lock(allsources { } block around it
lock (allSources)
{
ExchangeCommonDataSource RetVal;
allSources.TryGetValue(parSourceGuid, out RetVal);
return RetVal;
}
}
// private constructor; it is private so we can rely on the
// fact that we only provide factory method(s) that insert the
// new items into the main dictionary
private ExchangeCommonDataSource(Guid SourceGuid)
{
// if you didn't want to use a factory, you could always do
// something like the following without it; note you will
// have to throw an error with this implementation because
// there's no way to recover.
//lock (allSources)
//{
// ExchangeCommonDataSource Existing;
// ExchangeCommonDataSource.allSources.
// TryGetValue(parSourceGuid, out Existing);
// if (Existing != null)
// throw new Exception("Requested duplicate source!");
//}
// ... initialize ...
}
}
now to access, the client just needs to have some sort of key to access the data:
example: frmClientClass.cs
public partial class frmClientClass
{
ExchangeCommonDataSource myDataSource = null;
public void InitializeSource(Guid parSourceGuid)
{
myDataSource = ExchangeCommonDataSource.GetConnection(parSourceGuid);
}
}
I find this a generally more compelling solution that Option 1, simply because anything that has access to the class and an ID can get the data source, and because it's fairly easy to implement, and it gives automatic support for doing multiple instances of your data source class.
It has fairly low overhead, and since getting a data source is, in most cases, something that is not going to be done in tight loops (and if it were, you would have local copies, not looking them up from a dictionary every time) any small performance loss should be worth the ease of use. And, best of all, even if you start with one data source, you can easily extend your application to more without having to rewrite any code or go to any further effort.
For instance, a very quick way to use this assuming you only have one data source would be just to use a known value for your Dictionary key, and then you just can hard code that in your second for for now. So, for the example, you could just have the empty GUID as your key, and use that for both your forms. i.e. the Main Form or your first data form would call the create method with Guid.Empty to create the data initially, and then you can just use that to access it when the time comes to open your second form.
Option 3: The 'Singleton' Pattern Class
Okay, I'm not going to spend much time or write code for this one, but I would be remiss if I didn't mention it. It's very similar to option 2, except, instead of having a static Dictionary to look up multiple data sources, you create a class that has one instance of the class stored in a static property, and you prevent (via exception) any attempts to create more classes. Then, you set all constructors to private, have them throw exceptions if the static variable already contains an object, and you create a getInstance() method which returns the single instance of the class, creating it if it's null.
Now, there are some little thread-safety trickiness issues with this that you will need to understand to write a traditional singleton, so be sure to understand those (there are questions on StackOverflow dealing with the issue). If you don't need any particular knowledge to construct the instance of the class, you can avoid the issues by simply initializing the variable where you declare it e.g. static MyClass theInstance = new MyClass();, and I highly recommend doing that if you do ever use one.
I have used Singletons in the (fairly distant) past, and it's not that they don't occasionally have their uses, especially in embedded systems. But, this is not an embedded system, and almost every time I used a Singleton in a GUI application, I regretted doing it because I ended up eventually re-writing it into something that would allow multiple instances. If you really just need one copy, all you have to do is put a member variable in the class that uses it, say, your main form, and make sure that you don't ever create but one. Doing this, you could even use the pattern by setting a static flag in the class that you can trigger an exception on; set it to true when you first create the object, and then if that's true you can throw your exception.
Anyway, my personal first rule for when to write a singleton is: don't do it unless you are certain you will never need more than one. If it passes that one, then the second rule is: you are wrong, there is a way it could happen, so just write it as a normal class and handle the singleton-ness of it in some other way. :) Seriously though, the real rule is, just don't do it unless you have get some a very solid reason or a significant benefit from doing it.
Oh, and to reiterate: it's very possible to accomplish the pattern of singleton, without writing the canonical singleton class. The pattern is fine, just do it in a way that when that need for a second instance of that class comes along, there is a very low cost to eliminate the pattern.
Option 4: A Separate Class
Option 4 is very similar to Option 2, but implemented in a second class. (In fact, if you ever think you might have multiple sources of data, it would be worthwhile to just start here, although it's a little more time to set up initially.) Instead of having your static items as members of that class, implement another class that has something like them and provides access. This is a way to decouple the class itself from the creating of it. For example, if you were writing a library, and you wanted to provide several different types of data source, you could implement a base class and then derive your other objects from the base class, and then provide creation mechanisms via a class that gives factory methods to create the different kinds.
In a situation like this you very well may not even want whatever is using your data source to have to know anything about the implementation of the data source classes at all, and only go through the base interface, and this provides an easy way to do that. If you had to write it all as base class static members, then you would be forcing a rewrite of the base every time you derived a new class, and it would also be forcing the base to know something about the derived classes, each of which is, in general, something to avoid. In other words, it's not that it's never useful, but don't do it without very good reason, and don't do it without understanding the implications.
example: code for external class
InfostoreBase.cs
// our data source base class; could do interface instead like:
// public interface IInfostoreBase
public abstract class InfostoreBase
{
public abstract int Information { get; set; }
public abstract string NameOfItem { get; set; }
public abstract decimal Cost { get; set; }
// ... etc ...
}
InfostoreEnterprise.cs
public class InfostoreHomeEdition :
InfostoreBase
{
public override int Information { get { /* ... */ } set { /* ... */ }}
public override string NameOfItem { get { /* ... */ } set { /* ... */ }}
public override decimal Cost { get { /* ... */ } set { /* ... */ }}
public void SetFeatures(string parSomething) { /* ... */ }
}
InfostoreHomeEdition.cs
public class InfostoreEnterpriseEdition :
InfostoreBase
{
public override int Information { get { /* ... */ } set { /* ... */ }}
public override string NameOfItem{ get { /* ... */ } set { /* ... */ }}
public override decimal Cost { get { /* ... */ } set { /* ... */ }}
public void SetBaseDiscount(decimal parSomethingElse) { /* ... */ }
}
InfostoreProvider.cs
public class InfostoreProvider
{
static Dictionary<Guid, InfostoreBase> allSources =
new Dictionary<Guid,InfostoreBase>();
public static InfostoreBase
GetHomeConnection(Guid CustomerKey, string HomeFeatures)
{
lock (allSources)
{
InfostoreBase RetVal;
if (!ValidHomeKey(CustomerKey))
throw new
InvalidKeyException("not valid for Home Edition");
allSources.TryGetValue(CustomerKey, out RetVal);
if (RetVal == null)
{
RetVal = new InfostoreHomeEdition();
allSources.Add(CustomerKey, RetVal);
}
var ActualVersion = (InfostoreHomeEdition) RetVal;
RetVal.SetFeatures(HomeFeatures);
return RetVal;
}
}
public static InfostoreBase
GetEnterpriseConnection(Guid CustomerKey, decimal BaseDiscount)
{
lock (allSources)
{
InfostoreBase RetVal;
if (!ValidEnterpriseKey(CustomerKey))
throw new
InvalidKeyException("not valid for Enterprise Edition");
allSources.TryGetValue(CustomerKey, out RetVal);
if (RetVal == null)
{
RetVal = new InfostoreHomeEdition();
allSources.Add(CustomerKey, RetVal);
}
var ActualVersion = (InfostoreEnterpriseEdition) RetVal;
RetVal.SetBaseDiscount(CostBase);
return RetVal;
}
}
}
code in client class
private InfostoreBase myConnectionSource;
private void Initialize()
{
// ...
myConnectionSource =
InfostoreProvider.GetConnection(
myKey, isEnterprise, myData
);
//...
}
Closing
I think that covers a very good range of possible solutions; none of them is particularly hard to implement, and each has its own benefits and disadvantages. In general I would go for Option 2 or Option 4, but [broken record] it always depends on your exact situation. I think it would be fairly easy to use extend these to handle lots of different situations. And of course if there are any problems, just let me know.
Another possible way to handle this would be to create some interfaces to represent the role of data provider and data receiver, and then you would implement those interfaces on your form. It would be very similar to doing it with a common data source, but instead of running things through an object, you would implement the interfaces and the data can go directly where it is needed. It may be a bit more efficient that doing it through a DataSource, although it's hard to say without knowing all the specifics, but if you are really transferring loads of data putting it through a separate datasource could cost you some efficiency, especially if you never have a need for all the data in one spot.
In the example code here I'm showing what it would look like if you implemented your own event args for different types of data, this also could be used in a common data source for the events if you wanted to be able to have a little more granularity over what got sent when. (Please keep in mind I've typed this all in on the webpage without trying to compile it; this is supposed to give you the idea of how to do it, but its possible (I would estimate 100% change) that I didn't get everything in perfectly. :D)
public class FirstDataKindEventArgs : EventArgs
{
public FirstDataKindEventArgs(int parID, string parName, string parOtherInfo)
{
Id = parId;
Name = parName;
OtherInfo = parOtherInfo;
}
public int ID { get; set; }
public string Name { get; set; }
public string OtherInfo { get; set; }
}
// plus other event arg definitions
public interface IExchangeDataProvider
{
event EventHandler<FirstDataKindEventArgs> FirstDataKindReceived;
event EventHandler<SecondDataKindEventArgs> SecondDataKindReceived;
event EventHandler<ThirdDataKindEventArgs> ThirdDataKindReceived;
}
public interface IExchangeDataReceiver
{
void ConnectDataProvider(IExchangeDataProvider Provider);
}
then in your data providing form you would implement the interface:
public partial class MyProvidingForm : System.Windows.Forms.Form, IExchangeDataProvider
{
// normal form stuff
// ...
#region IExchangeDataProvider
public event EventHandler<FirstDataKindEventArgs> FirstDataKindReceived;
public event EventHandler<SecondDataKindEventArgs> SecondDataKindReceived;
public event EventHandler<ThirdDataKindEventArgs> ThirdDataKindReceived;
public void FireDataReceived(EventArgs Data)
{
FirstDataKindEventArgs FirstKindData = Data as FirstDataKindEventArgs;
if (FirstDataKindEventArgs != null)
if (FirstDataKindReceived != null)
FirstDataKindReceived(FirstKindData);
//... etc.
}
public void GotSomeDataOfTheFirstKind(int TheID, string SomeName, string Other)
{
FirstDataKindEventArgs eArgs =
new FirstDataKindEventArgs(TheId, SomeName, Other);
FireDataReceived(eArgs);
}
and in your receiver form(s) or other classes you wish to receive data:
public partial class FirstDataKindReceivingForm :
System.Windows.Forms.Form,
IExchangeDataReceiver
{
// usual form stuff
// ...
private IExchangeDataProvider myDataProvider;
public void ConnectDataProvider(IExchangeDataProvider Provider)
{
myDataProvider = Provider;
myDataProvider.FirstDataKindReceived +=
new EventHandler<FirstDataKindEventArgs>(
HandleFirstKindOfDataReceived
);
}
private void HandleFirstKindOfDataRecieved (
object sender, FirstDataKindEventArgs
)
{
// do whatever with data
}
}
#endregion
}
and so forth.
edit Form2 's constructor, so that you can pass some values from Form1 while running a new Form2 with .Show or .ShowDialog
Form2 myForm = new Form2(value1, value2, value3 ...);
And on Form2.cs you shall convert (or add a new one) public Form2() to public Form2(var value1, var value 2...)
If you have to send to Form2 continuously data, you may use a shared memory or shared data file.
The answer in the db forum by Mahrous seems to be the simplest http://www.daniweb.com/software-development/csharp/threads/126879/617436#post617436
Some of the other solutions are also valid and may be appropriate depending on the design of the applicaiton.
I almost never used (advanced, or at all) graphical interfaces, or one simple form with simple controls... but this time I've got something a little more complex, and I don't have much experience with GUI.
I have one main form (and possibly more in the future) from which other sub-forms open (and they might have sub-forms of themselves) and I wonder what is, in your opinion, the best way to communicate between them?
I thought of passing the main form as a parameter to the constructors of the sub-forms, but it doesn't seem like a good way, especially if I'm going to need to communicate between other, distinct, sub-forms, not to mention I have to double check the input, or make a few methods, but it seems more like functional programming than object oriented programming...
Perhaps I can:
Create a static class (or Properties.Settings) for global settings. Cons: every change of data is needed to be copied to the class, I'm looking for something a bit more comfortable and elegant.
Use the ugly way of accessing the controls from Application.OpenForms - fixes the problem of passing the main form as parameter. Cons: not very stable.
Do something else I haven't thought of. Suggestions? Cons: don't know what it is yet.
Your constructor idea is probably the most sound method of communication back to the main form. Your sub form would do something like the following:
public class SubForm : Form
{
public SubForm(MainForm parentForm)
{
_parentForm = parentForm;
}
private MainForm _parentForm;
private void btn_UpdateClientName_Click(object sender, EventArgs e)
{
_parentForm.UpdateClientName(txt_ClientName.Text);
}
}
And then you expose public methods on your MainForm:
public class MainForm : Form
{
public void UpdateClientName(string clientName)
{
txt_MainClientName.Text = clientName;
}
}
Alternatively, you can go the other way around and subscribe to events from your SubForms:
public class MainForm : Form
{
private SubForm1 _subForm1;
private SubForm2 _subForm2;
public MainForm()
{
_subForm1 = new SubForm1();
_subForm2 = new SubForm2();
_subForm1.ClientUpdated += new EventHandler(_subForm1_ClientUpdated);
_subForm2.ClientUpdated += new EventHandler(_subForm2_ProductUpdated);
}
private void _subForm1_ClientUpdated(object sender, EventArgs e)
{
txt_ClientName.Text = _subForm1.ClientName; // Expose a public property
}
private void _subForm2_ProductUpdated(object sender, EventArgs e)
{
txt_ProductName.Text = _subForm2.ProductName; // Expose a public property
}
}
A good way is to declare delegates in the form that want to start the communication. You need a delegate and a callback function:
public delegate void SetValueDelegate(string value);
public SetValueDelegate SetValueCallback;
Another form can then attach to this delegate. At that moment both forms have to know each other, but not after that moment:
firstForm.SetValueCallback += new SetValueDelegate(secondForm.SetValueFunction);
The second form has to declare a function that matches the delegate definition:
public void SetValueFunction(string value)
{
// do something
}
Now the first form can use the delegate to use the function of the second form (and all other forms or classes that were attached to the delegate:
SetValueCallback(txtParam.Text);
Edit: made an complete example
using System;
namespace DelegateTest
{
public delegate void SetValueDelegate(string value);
public class Class1
{
public SetValueDelegate SetValueCallBack;
public void Test()
{
if(SetValueCallBack != null)
{
SetValueCallBack("Hello World!");
}
}
}
public class Class2
{
public void SetValueFunction(string value)
{
Console.WriteLine(value);
}
}
public class Launcher
{
public static void Main(string[] args)
{
Class1 c1 = new Class1();
Class2 c2 = new Class2();
c1.SetValueCallBack += new SetValueDelegate(c2.SetValueFunction);
c1.Test();
}
}
}
The most flexible, scalable (and IMHO the most professional) way to do it is to use CAB (Composite Application Block). In simple terms CAB is a set of 2-3 assemblies that implement a lot of plumbing required to make complex UI applications the right way and it exposes this plumbing to the user of the library in a nice way. Among others it has a very nice event and command (as in command pattern) system.
The downside: requires some time to learn and not very trivial to grasp.
Here is a comprehensive (but easy to understand) tutorial that will help you make the learning easier.
You can use the built in Tag property of the form which is an "object" class.
public Form1()
{
(ComplicatedDataStructure)Tag = new ComplicatedDataStracture();
}
.
.
form1 = new Form1();
.
.
form2 = new Form2();
.
.
form2.Tag = form1.Tag;
so form2.Tag is equals to "ComplicatedDataStracture" object;