Category: .net (c#)

Example by Parable and Analogy

I have a secretary. At the end of the day, I ask her to: (i) take the firm’s outgoing mail and to drop it off at the post office, and in addition to that, after she has dropped the mail off, I ask her to do something else: (ii) whatever task I wrote for her on one of those sticky notes. Now, what is the task on the sticky-note? It depends on the day. Sometimes it might be to: (i) purchase some stationary. Other times it might be to: (i) file some papers, (ii) send some emails, (iii) print some documents etc.

Suppose on this particular day, I require her to print off some documents. In summary, first, she needs to drop off the mail and immediately after that is done, she needs to print off some documents.

Applying the story to some techno-computer geek speak

The method name in this case is: DropOffMail. And the call back function is: PrintOffDocuments. The PrintOffDocuments is the call back function because we want the secretary to do that, only after PrintOffDocuments has run.

So I would “pass: PrintOffDocuments as an “argument” to the DropOffMail method. Now the DropOffMail method must be able to accept functions in its method signature. After the DropOffMail is run, then the call back function, PrintOffDocuments would be called and would run.

So in short, the mail would be delivered, and she would run a print job (which would be the call-back function).

I hope that was simple enough for you!

For those wanting a simple answer without the geek-speak, I’ll try to explain:

Normal Collections

Every now and then I go to NYC and my friend asks me to buy stuff for him. So I take a shopping list with me. The list has a lot of things on there like:

1. Hugo Boss jacket
2. Clive Christian’s Imperial Majesty ($215,000/16.9 oz.)
3. Mont Blanc – pen. $500.
4. Fur coat. ($4500)
5. Ferrari ($750,000)

Well I”m not buying that stuff. Way tooo expensive! So I cross them off and remove them from the list and I add in:

1. 12 dozen Titleist golf balls.

The ObservableCollection

So I come home and my friend is not pleased. But that was in the old days, now he’s got onto this whole smart phone thing – and he now has an Iphone with an IShoppingList app that’s on the cloud. Here’s how it works: whenever you remove something from the online shopping list on the cloud: he gets a notification on his phone (i.e. an sms or email etc) and in addition to that stuff happens. What happens exactly? Usually a phone call asking me to put the stuff back on the list.

The observable collection works just the same way. If you add or remove something to or from it: someone is notified. And when they are notified, they do stuff. What stuff exactly? Well whatever you want! they can sing, dance, do the hokey-pokey etc.

That sums it all up!

Synchronous Execution

My boss is a busy man. He tells me to write the code. I tell him: Fine. I get started and he’s watching me like a vulture, standing behind me, off my shoulder. I’m like “Dude, WTF: why don’t you go and do something while I finish this?”

he’s like: “No, I”m waiting right here till you finish it off”. This is synchronous

Asynchronous Execution

The boss tells me to do it, and rather that waiting right there for my work, the boss goes off and does other tasks. When I finish my job I simply report to my boss and say: “I’m DONE!” This is Asynchronous Execution.

…….it really boils down to something as simple as that!