"Douglas Peterson" <Tergiver@nospam.msn.com> wrote in message
news:%23tb$hFZ7GHA.1188@TK2MSFTNGP05.phx.gbl...
>I created the following code:
>
> private struct StackItem
> {
> public EventHandler theEvent, theHandler;
> public StackItem(EventHandler theEvent, EventHandler theHandler)
> {
> this.theEvent = theEvent;
> this.theHandler = theHandler;
> }
> }
>
> protected void AddHandler(EventHandler theEvent, EventHandler theHandler)
> {
> theEvent += theHandler; // add handler to event
> stack.Push(new StackItem(theEvent, theHandler)); // note the fact that we
> did so
> }
>
> public virtual void Dispose()
> {
> while (stack.Count > 0)
> {
> StackItem si = (StackItem)stack.Pop();
> si.theEvent -= si.theHandler; // remove the handler from the event
> }
> }
>
> So that my derived classes can register for various events of various
> controls on my form without having to make certain to add both the
> subscribe and unsubscribe lines of code. However, the following code:
>
> AddHandler(form.listView.SizeChanged, new
> System.EventHandler(this.listView_SizeChanged));
>
> gives the following error:
>
> "The event 'System.Windows.Forms.Control.SizeChanged' can only appear on
> the left hand side of += or -="
>
> I assume this is some attribute of the SizeChanged member of the various
> stock controls. Is there any way around this?
>
> Why do I need to unsubscribe? Because I'm using objects to implement
> various states in my application. When the app changes states it needs to
> unhook the current state object from all events so that the new state can
> take over.
>
>

>I created the following code:
>
> private struct StackItem
> {
> public EventHandler theEvent, theHandler;
> public StackItem(EventHandler theEvent, EventHandler theHandler)
> {
> this.theEvent = theEvent;
> this.theHandler = theHandler;
> }
> }
>
> protected void AddHandler(EventHandler theEvent, EventHandler theHandler)
> {
> theEvent += theHandler; // add handler to event
> stack.Push(new StackItem(theEvent, theHandler)); // note the fact that we
> did so
> }
>
> public virtual void Dispose()
> {
> while (stack.Count > 0)
> {
> StackItem si = (StackItem)stack.Pop();
> si.theEvent -= si.theHandler; // remove the handler from the event
> }
> }
>
> So that my derived classes can register for various events of various
> controls on my form without having to make certain to add both the
> subscribe and unsubscribe lines of code. However, the following code:
>
> AddHandler(form.listView.SizeChanged, new
> System.EventHandler(this.listView_SizeChanged));
>
> gives the following error:
>
> "The event 'System.Windows.Forms.Control.SizeChanged' can only appear on
> the left hand side of += or -="
>
> I assume this is some attribute of the SizeChanged member of the various
> stock controls. Is there any way around this?

>
> Why do I need to unsubscribe? Because I'm using objects to implement
> various states in my application. When the app changes states it needs to
> unhook the current state object from all events so that the new state can
> take over.
>

"Christof Nordiek" <cn@nospam.de> wrote in message
news:esDiTYd7GHA.4604@TK2MSFTNGP03.phx.gbl...
> possible solutions:
> 1. for every Event make a static method, wich is subscribed once and calls
> the appropriate handler on the actual stateobject.
>

> 2. make two methods wich do all the subscribing and unsubscribing of the
> event.
>

> 3. store the old state object, and for every event make a method or
> codeblock wich does the subscribing and the unsubscribing:
> if (olsState != null)
> control.Event -= oldState.Handler();
> control.Event += newState.Handler();
>

> 4. in the StackItem store the MemberInfo of the event.