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objectInstance.Property.Method() Invocation in C#

I'm learning ADO.NET and here is an example of method call from MS Documnetation:
workAdapter.TableMappings.Add("AuthorsMapping", "Authors");
Where workAdapter in an instance of DataAdapter class, TableMappings its property, and Add its method. I have never seen method being invoked in this way. I wasn't able to find an answer here nor in the documentation. Need help understanding this.

Properties and methods are invoked this way a lot. You can chain as many together as you like and it makes sense to do so if you only need to use each one once. Any time you could assign something to a variable and then access a member via that variable, you can access it for what you originally assigned. If you have these types:
public class Thing
{
public Stuff Stuff { get; set; }
}
public class Stuff
{
public void DoSomething()
{
// ...
}
}
then you could do this:
var s = new Stuff();
var t = new Thing { Stuff = s };
s.DoSomething();
t.Stuff.DoSomething();
In those last two lines, s refers to the same object as t.Stuff so you can call the same DoSomething method on both.

C# generic return with generic type set in the method not in the call

I am trying to setup a method that retrieves data from a database, and based on data in there it will create and hydrate a class with a generic component.
public class MyObject<T> where T : BaseMyType
{
T MyTypedObject { get; set; }
}
public class MyType1 : BaseMyType
{
string Key { get; set; }
}
public class MyType2 : BaseMyType
{
Guid Id { get; set; }
}
public MyObject<T> MyMethod<T>() where T : BaseMyType
{
if(Situation1)
return new MyObject(MyType1);
else
return new MyObject(MyType2);
}
This code complains that MyObject<MyType1> cannot be converted to MyObject<T>. Now I need to use it like this:
var myObject = MyMethod();
The call of course complains it cannot infer the type from the usage. I understand the compiler error messages, I just am not sure how to do what I need.

It can't be done, but…let's suppose for a moment that we could figure out a way for the following statement to compile in the way that you want:
var myObject = MyMethod();
Then what is the code using myObject going to look like? In this hypothetical scenario, the variable myObject will sometimes have the type MyType1 and sometime have the type MyType2. Will the code using myObject care about that?
If all that code will do is use members of the shared base type (i.e. BaseMyType), then the fix is easy. Just forget about the generic approach:
public BaseMyType MyMethod()
{
if(Situation1)
return new MyType1();
else
return new MyType2();
}
If it does care about the differences (i.e. needs to access either Key or Id depending on the type that was returned), then even if you could do the impossible, the calling code is still going to need to conditionally handle the individual scenarios based on the Situation1 variable. Which would mean that you put the check for Situation1 in the wrong place.
Instead, your caller should look more like this:
if (Situation1)
{
MyType1 myObject = MyMethod1();
// do situation 1 stuff
}
else
{
MyType2 myObject = MyMethod2();
// do situation 2 stuff
}
Where the implementation of your original MyMethod() has been split into two methods, MyMethod1() and MyMethod2(), corresponding to the two scenarios. Again, note the complete lack of generics as part of the implementation. It's not called for, and won't work.
It's even possible that you need a polymorphic implementation of the caller, i.e. so you don't have to check Situation1 more than once. But without a good, minimal, complete code example it would be impossible to comment more thoroughly on that possibility.

How to check the type of a list if inheritance is used

I'm currently working on a C# program that creates a List, of object Task, the object Task is a base class and many other inherit from it. What I want to is compare the type of one of the object within said list to see which form should be opened in order to edit it.
This is the code I have already created.
private void itemEdit_Click(object sender, EventArgs e)
{
int edi = taskNameBox.SelectedIndex;
Task checkTask = todoList.ElementAt(edi);
if(checkTask.GetType is Note)
{
noteBuilder editNote = new noteBuilder(todoList);
editNote.Show();
}
else if(checkTask.GetType is extendedTask)
{
extendedTaskBuilder editTask = new extendedTaskBuilder(todoList);
editTask.Show();
}
else if(checkTask.GetType is Reminder)
{
reminderBuilder editReminder = new reminderBuilder(todoList);
editReminder.Show();
}
else if (checkTask.GetType is Appointment)
{
appointmentBuilder editAppointment = new appointmentBuilder(todoList);
editAppointment.Show();
}
}
On a secondary note would it be easier if instead of passing the list between the forms and generating a new object of the form that display information that I instead pass a single object between forms and just update the form every time a new element is added to the list.
Many thanks

Have you tried checking like this:
if (checkTask is Note)
{
}
...

Have you considered creating a base class for all types you are now switching between and call a virtual (abstract) method?
Put all code now in the if in the overridden abstract method.
Advantages:
- The intelligence of the switch is within the classes where it belongs.
- When a new type is added you get a compiler error to also add this feature to the new type.

I suggest that instead of doing that series of ‘if’ clauses, you use inheritance to achieve what ou need. First you create a virtual method in your base class. A virtual method means it won't have any implementation in the base class, only the declaration:
public class Task
{
(...)
public virtual void ShowEditForm(IList todoList);
(...)
}
Then you create the child class methods (I'm assuming the todoList object is a IList, but just change it if it is not).
public class Note: Task
{
(...)
public override void ShowEditForm(IList todoList)
{
(new noteBuilder(taskToEdit)).Show();
}
(...)
}
public class Reminder: Task
{
(...)
public override void ShowEditForm(IList todoList)
{
(new reminderBuilder(taskToEdit)).Show();
}
(...)
}
I didn't write all the classes, but I think you've got the idea. To call the method, you just call the method from Task class, and the right method will be executed:
int edi = taskNameBox.SelectedIndex;
Task checkTask = todoList.ElementAt(edi);
checkTask.ShowEditForm(todoList);
This way, when you want to create new types of Task, you just have to create the child class, with the proper method, and the inheritance system will do the rest.
One more thing, the override keyword in the child method declaration is important, because it says to the compiler that this method should be called even if you call it from the BaseClass.

First, to your second note. What you are talking about doing is having a global object that all forms refer to in some parent. That can work, however you will need to make sure there is some mechanism in place that makes sure all of the forms are synchronized when one changes, and this can get messy and a bit of a mess to maintain. I am not necessarily advocating against it per say, but just adding words of caution when considering it :)
As to your posted code, it would probably be better to turn this into a Strategy Pattern approach, where all forms inherit from a base class/interface which has a Show method. Then all you need to do is call checkTask.Show(todoList);. If you do not want that coming from the Task, then you could have your forms all inherit from the above base and you could use a factory pattern that takes in the Task and list and returns the appropriate form on which you simply call form.Show();

Code like this is difficult to maintain, you are probably better off abstracting this out, like so (assuming Task is not the one included in .net):
public interface IBuilder
{
void Show();
}
public abstract class Task
{
// ...
public abstract IBuilder GetBuilder(TaskList todoList);
// ...
}
public class Note : Task
{
public override IBuilder GetBuilder(TaskList todoList)
{
return new noteBuilder(todoList);
}
// ...
}
// etc.
private void itemEdit_Click(object sender, EventArgs e)
{
int edi = taskNameBox.SelectedIndex;
Task checkTask = todoList.ElementAt(edi);
IBuilder builder = checkTask.GetBuilder(todoList);
builder.Show();
}
Alternately, you can use an injection pattern:
public abstract class Task
{
protected Task(Func<TaskList, IBuilder> builderStrategy)
{
_builderStrategy = builderStrategy;
}
public IBuilder GetBuilder(TaskList todoList))
{
return _builderStrategy(todolist);
}
}
public class Note : Task
{
public Note(Func<TaskList, IBuilder> builderStrategy) : base(builderStrategy) {}
}
// ...
note = new Note(x => return new noteBuilder(x));

Passing continuous data between WinForms

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.

Reference calling assembly instance in C#

.Net 3.5 sp1 available type question ...
Is it possible to "get a handle" or reference to the actual instance of an assembly that called a method? I can get the executing and calling assembly via reflection, but what I'm after is not so much the assembly, but the INSTANCE of that assembly that called method.
Simple example (maybe):
interface IBob
{
int Id { get; }
void Foo();
}
public class Bob : IBob
{
private int _id = 123;
public int Id
{
get { return _id; }
}
public void Foo()
{
new OtherAssemblyClass().Bar();
}
}
public class OtherAssemblyClass
{
public void Bar()
{
//
// what I want to do here is get a reference
// to the calling INSTANCE of IBob and determine
// Bob's Id ... so something like:
//
// int Id = (System.XXX.GetCallingAssemblyInstance() as IBob).Id;
//
//
}
}
The real situation is a bit more complex than this, and precludes the obvious passing of IBob instance as a parameter in OtherAssemblyClass.Bar(), although that may be end result.
Entirely possible I'm just being stupid too, and not seeing obvious. 2 x 4 corrections to skull also welcome.

Unfortunately you can't get the instance unless it's passed in. You can find out what's calling your method by using the StackTrace.

PostSharp is the only way I would know of to make that work. Take a look at the InstanceBoundLaosEventArgs class. Warning: this is a pretty big deal, and a serious addition to the weight and complexity of your architecture, especially at build time.

I can get you halfway there if you are willing to use extension methods. Here's an example:
public static void Bar(this IBob CallingIBob)
{
int Id = CallingIBob.Id;
}
...and calling Bar():
public class Bob : IBob
{
#region IBob Members
public void Foo()
{
this.Bar();
}
public int Id
{
get { throw new NotImplementedException(); }
}
#endregion
}
Yes, it's not the exact case you were looking for, but functionally similar. Bar can be called from any bob and it will have a reference to the calling bob without explicitly passing in the instance.
I understand that you may want to call Bar in another assembly of your choice. Maybe Bar is defined in a base class and you are calling specific implementations of it in subclasses. That's ok, use the extension method to take in information about the specific Bar you are trying to access and route accordingly.
Please update your post with a more concrete problem definition if you would like a more specific solution.