Command Pattern - Design Patterns (ep 7)
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- Опубліковано 13 лип 2017
- Video series on Design Patterns for Object Oriented Languages. This time we look at the Command Pattern.
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2023 and still one of the best Design Pattern Playlists.
Student: Can we do this one by one?
Christopher: Yes, let's do it one by one by one by one.
Your design pattern playlist is one of the best explanations about patterns ever. The last video of this playlist is over 4 years old and there are many patterns left (visitor, chain of responsibility, flyweight, builder, etc.). Are there any plans to cover these ones? It would round this awesome playlist more up :)
It's been more than 5 years for this video yet no one has ever touched your level of explaining things. Simply a gem. It's high time now , please make more such videos.
In my youtube browsing career of 9+ years,this is the first channel/video where I am commenting and liking.
You really deserve this.Hats off to you Christopher Okhravi
Thank you for sharing. I very much appreciate you taking the time to punch out that comment. I am humbled.
At around 25:20, Chris mentions that command pattern is similar to strategy pattern, and he wasn't sure what the technical difference was. To me, the difference is that in the strategy pattern, the object that gets passed around is an algorithm (i.e. HOW to do something). On the other hand, in the command pattern, the object that gets passed around is a command (i.e. WHAT to do).
For example, let's say we have a list of elements. If we already know that we want to sort the list, we might use the strategy pattern to determine how to sort the list. On the other hand, we might use the command pattern to determine what operation to apply to the list, such as to sort the list, or to add an element, or to remove an element, etc.
I agree with this. And I see how the Command can then use the Strategy pattern within itself, to "execute" and "unexecute" depending on what that is.
Well... in the simplest of terms, both are encapsulating BEHAVIORS. In one context (Strategy), you calling the behavior ALGORITHMS, and in this context (Command), the algorithm is the message or command. The only difference I see is that, for Strategy there is no requirement to undo something that was done in the past. You could say that the Command Pattern is an EXTENSION of the Strategy Pattern.
I kinda agree with Professor F here. Command Pattern just feels like Strategy Pattern with an Undo operation.
I can also see that a subtle difference might be the way the client (Invoker in this case) is using the commands. For instance the order of commands generally matters, so the Invoker would keep track of the commands if they wanted to Undo commands in the order of which they were last executed. While in the Strategy Pattern, clients typically do not need to maintain a collection of strategies where order matters. Of course this is all depending on the scenario. Of course you could create composite hierarchies for both commands and strategies, and then again commands can contain a strategy. So it really all depends on the scenario, but I think in the simplest example we are keeping track of what to either do or undo in relation to the order in which the commands were executed.
Strategies aren't really meant to be passed around, stored, sent over the network, reversed etc. Commands are.
It's the data the command contains, sometimes just the command itself, that defines _what_ should be done and the execute function defines _how_ it should be done.
You deserve more subs man. One of the few people I can actually stomach when talking and design patterns.
Hahah I much appreciate being stomach:able :) :) Thank you very much for watching and for sharing :)
I totally agree !
totally agree
Totally agree
Boring as hell
I wish I had these videos back when I studied CS.
You show off everything about the patterns. The What, the How and the Where. Some of these patterns I fully understand now, 8-10 years later.
This is "Mr Bean" 30 years younger teaching Design patterns! Good job on your videos 💯
Christopher in 2017: One half is the office part and other half is the leisure part of your room.
2020: Yes
haha :(
I'm from Argentina, and I'm studying Information Systems Engineering , and in systems design subject my partners and me are studying Desing Patterns. Your explanations are great for us. Thanks a lot!
I could listen to you talk about Design Patterns forever!
Trough out the years i always come back to this channel when it comes to patterns. Noone explains it close as well as you do. Thank u alot
THis is really, really good content. I love how you discuss your own opinions on how these patterns are constructed.
I was really struggling to wrap my head around this one, just because there is a lot of verbiage thrown around very quickly, making it hard to latch onto anything in every other explanation. I really needed the time you took to break out down, rephrase sentences, etc. It's much simpler than everything else made it seem! Thank you so much for making this!
I studied few patterns from your video only and they were asked in an interview...followed your style of explaining the patterns and I got selected..thanks man. Your knowledge inspires and motivates me to learn more. ✌
Normie
I knew you won't fail us man! I was waiting for the next one since the last dp video :)
Thanks for sticking around :)
This was so good I feel genuinely mind-blown! The command pattern is crazy powerful
The beginning of these videos always makes me giggle with that goofy entry of yours 😂😂
Спасибо большое Christopher. У тебя хорошо получается объяснять такие сложные темы простыми примерами из жизни. Как раз то что я искал. Удачи тебе.
I've been waiting for the next instalment in the design pattern series. Love and appreciate your videos!
21:09 you alright my man? :D
Thank you Chris. I was afraid of tackling design patterns as a self taught but you have made this portion of the journey so much easier. Keep going man. Your amazing!
Only of the super rare videos that I watch at normal speed, which tells you a lot. :)
I really love your way of explaining man, it's simple and you cover all the important stuff. I subbed!
"Wi-Fi connected coffee machines?" - I'd never let my wi-fi drink my coffee!
I am impressed by the way you make us understand 'Design patterns'. Thanks a lot Christopher Okhravi
Not a problem. I’m glad to have been useful :) Thank you for watching and for your comment :) :)
Great explanation! I have been watching this series and so far this one is the first to make me actually laugh out loud :D 21:09
Heheh :) It was actually worse but I felt too much like a buffoon and had to cut the rest of the fall out :D
Once this entire patterns episode done. You could post that videos as bloopers :P
he just showed the feature of redo. "so the command ..." redo() "so the command..."
@@Ivo68 HAHAHHAHAHHAAHA
thanks man really helped me out. Really chill way of explaining things
Thanks, Christopher, it was a wonderful explanation. I have started this Design Patterns playlist a few days ago and I got addicted to it as you made them so easy to understand.
I am about to start my next semester learning all these patterns. Thank you for covering them! Also 21:10 was seriously hilarious! You're comedic skills are on point!
Wonderful! I'm trying to learn to program and I was deferring learning about design patterns because they seemed too complicated. Your videos have changed my mind and I am managing to understand every single one of them.
Your way of teaching is simply superb! :D Keep up the good work! :)
A great approach to explanation, MR Okhravi!
Thanks for the video!
I really appreciate this series. I prefer this before any other series in Netflix 😎 You make me laugh loud and in the same time give me understandable patterns ✌🏽
I have an exam tomorrow about all the design patterns you helped me a lot!
The kapuuusshh always gets me after the definition.
Best series on Design Patterns. Binge-worthy. Thanks a lot.
Thank you man, never had time to finish reading this, book and yeah, you explain it will enough that I can follow and not trail off.
A more frequent variant of the Command Pattern, which is more prominent in business application development, is one which implments the methods `canExecute()` and `execute()`. For example if you have a UI with context buttons. Each button holds the action of a particular item in the menu and whether it can be executed. And according to the canExecute state the item is either greyed-out (not pressable) or active and ready to be pressed.
I built an AT Command Builder in order to build specific routines to program a network module. I didn't know that was a design pattern. My head exploded with this awesome video! :) Thank you, Christopher! amazing videos!
awesome! I begin to love design patterns after seen your good explanations! great job!
You saved my life. Thank you for the series on design patterns. You are really good at explaining things
Love your videos and way of explaining it. I have confidence that now I can also learn design patterns.
Thank you so much for all your videos. They are VERY helpful along with reading the book
+Callerooo Thank you. I'm glad to hear that the videos help support the literature :) Thank you for watching and for commenting! :D
Thank you! Thank you! Thank you! I am an auditory learner which is a very serious challenge to learning programming. I've read the books, read the sites, and watched a few other videos to try to understand this pattern to no avail. Within 5 minutes of watching this I understood more than all those other resources combined. Don't change a thing! I know visual learners may not appreciate your work the way I do but I also know that the resources out there are hand made for them.
Videos like yours make me wonder why I even bother with most of my uni classes where the explanations are often unclear.
This is so well explained and it probably saved me a few hours of studying. Thanks!
I'm pretty late to comment, but just saw these videos. WONDERFUL! one of the best I've even come across. Thank you so much Sir.
Another example would be building a calculator:
We have multiple Commands: Add, Subtract, Multiply, Divide, Redo, Undo
We have a Calculator which has buttons that invoke these commands.
Then our receiver which is the display, shows the results of those commands.
I'm loving these videos! Starting to see the world in a brand new way! Thank you so much!
I'm new to design pattern and at the end I was like, "yoooooooo!!! This is amazing!!! Where do I start 👀👀? “ Your episodes on these are awesome. I love how you explain these in several examples and in different view points along with real world applications and most of all the example of code. This is how I learn and I wish I had someone to explain things to me in the way you do. Thanks 😉👌👍👍
When they print a new edition of the book they should reference to this series :)
Very well explained. Like the way you present the topics. Respect.
Can't wait for the next one...
I've been watching 20+videos these days to get this pattern, this is the one that made me understand what it is !!! thank you so much
I really want to say thank you so much. I don't learn from just reading books very well but I can learn great from fantastic lecturers such as yourself. I've actually read this book but my understanding of design patterns has increased so much from your videos. Thank you. Really I mean it, thank you so much. You have helped me become a much better developer.
Please complete all design patterns not only the ones covered in Head First Design Patterns, but your videos are also so good I really love these design pattern videos a lot
I like your way of teaching. Thanks a ton for making things simpler. You rock!!
This is the super easy to grasp man.... I'm watching this now, after learning Design patterns before 10+ years back.. I worry, I didn't have UA-cam and videos like yours in those days.
Second time i watch this. Great explanation and real example !! :) Like i heard good material always should be inspected twice, because you want to get all information clear.
at least twice* :)
Another excellent explanation of design patterns. Thanks for these videos. By the way that 21:09 was amazing. I just rolled back to see that again :)
Man I'm really amazed with this explanation!! Mind blowing!!! If I could put all my former university teachers to give a class like that, they wouldn't be capable to do it... Congrats Christopher, you are doing an amazing work...
Thank you for the AWESOME videos! Really helped me a lot!
You are just awesome....I'm very new to design patterns...and this video really helped me understand...Thanks alot...😊😊
Thanks so much for this video. I just started working through Head First Design patterns and you are helping me expodite the process (I'm not a big fan of reading to learn programming simply because audio is more efficient)
you ll most likely make me pass my exams with these clear explanations! Thank you
I’m glad to hear! Best of lucks! :)
Very well explained. Able to understand the command pattern with clarity. Thanks a lot.
For me this series is extremely useful. Thank you!
Best series on design patterns on youtube
It's finally up. Liked before watching.
Christopher, you are an awesome tutor, great explanation, and feels having discussion realistic and face to face, Thanks... Please keep it up
Was struggling with the Command pattern until I found your video, very clear explanation. Thank you so much!
no man, you are TOTALLY AWESOME!!
Make more videos! Loved your design pattern series, in fact all of the codewalks too
Thanks for this playlist. I find it extremely useful
Please continue the series man. great explanations.
21:10 scared the shit out of me I thought someone in my room fell. Also: you should make videos again! I've been watching quite a few of your design pattern videos the past week and I've really been enjoying them.
I think the same kind of videos but with data structures and algorithms would be super super cool!
Amazing tutorial! Don't stop uploading : ) Subscribed!
Your videos are great! They got me an A in my programming exam about Design Patterns :D! Well explained, easy to follow, and entertaining. Thank you
After watching this video I went smart home 🤣
Excellent video as usual. The Hue control is a fantastic real world example!
A crystal clear explanation, well done! Videos length don't matter when video is rich in content
Great Explanation Christopher! Thank you very much for this video!
Hey Christopher, I'm new to C# and wanted to say a huge thanks for this video, its entertaining as well as educational - I can now follow some code at work and understand better - top job my friend !
Thank you for the amazing video series -:) This was pretty awesome.Having said that,i felt the way this scenario was implemented in HeadFirst book(using setCommand method to map a particular slot to an implementation of ICommand interface) seemed a bit better /made a bit more sense
Spent 30 seconds on this and immediately Subscribed.
Thank you so much for the explanation. Great work.
Love these videos! They are very clear and useful
Thank you for this film and every other. Great job 😊
Regarding the Undo & Redo via the Command pattern, you would have 2 stacks. When you perform an action you push it onto the Unto stack and clear the Redo stack. If you undo something you pop it off the Undo stack, undo it, and push it onto the Redo stack. If you redo something you pop it off the Redo stack, do it, and push it back onto the Undo stack.
+Chris Just Thanks for the clarification! Excellent idea. Makes perfect sense. That would be much easier than using an index variable that keeps track of where we are in the "undoing" which is kind of what I was alluding to. Thanks again and thanks for watching :)
I'm not convinced that Command Pattern would be a good tool for implementing a undo/redo functionality. I'd rather use immutabe state objects and store older instances in an undo list. You'd have some memory overhead but you wouldn't have to actually calculate undo and redo. Instead you just link to a different state.
@@ChristopherOkhravi Photoshop and most similar software use the state machine to manage workflows and the command pattern is one component of it. I am not 100% sure, but they use a single "stack" because it represents the "state" and can be rolled back and forward.
If you are really curious, check parametric modeling.
Thanks a lot for your videos, they are superbly helpful!
@@shobhit0shri Very interesting! Thanks :)
Christopher Okhravi , Shobhit Shrivastava , Tekay37, There is a talk by Sean Parent (the guy behind the Photoshop) called ``Run-time Polymorphism...'' where he explains the undo/redo model of Photoshop. They make some kind of copy of each state. Just watch the video, he demonstrates all the crazy things you can do, like slightly modifying one operation somewhere in the history without rolling back to that operation. He also explains how you achieve such kind of things.
Nice explanation, thank you for sharing with book titles in order to study it thorougher .
you definitely are the best lecturer/teacher I have ever seen .... so brilliant
Was watching and watching. Scrolled down to subscribe, and I already am...
great work bro.. I am an experienced developer without much knowledge on design pattern. I tried many tutes, but yours is the best. thank you very much
Fantastic, Wonderful explanation , Thumps up. Waiting for another Design patterns
best series on patterns online
Thank you very much been tryna understand this command but I feel this is the first time I actually got a good hang off it plus I think i am more likely a visual learner
awesome video ! It really helped me out understand the command pattern. Thank you very much !
Superb explanation! Thank you so much!
Thank you very much for the lucid explanation!
Thank-you sir for the series.
Now I don't need to get bored with the book.I get the point fast and furiously:) OK, I play the video in 1.5x speed sometimes, but you've done a GREAT JOB here. Thank you!
this is so very enjoyable, I am having a great time reading this book and watching your videos. thanks!
Best explanation I have come across. Hope you do similar videos for Head First OOAD book as well.