you saved my life man! thank you soo much this is perfect i understood everything, you're such a great teacher!!! i'm gonna be recommending memberships for your website to _EVERYONE_
Lot of respect for you sir! I want to switch to Kotlin and try to find some good tutorials. I must say no one is better than you in android here on UA-cam! Thank you soo much for these videos.
Just like your teaching skill a lot, U r a great teacher, the most imp thing in this video is how you build a repository class...Thanks again for the great stuff.
Timestamps: 00:00 - Intro 01:51 - What is a singleton? 04:26 - Practical example of a simple singleton in code 06:09 - Actually writing the singleton class 09:45 - A real, much more practical example 10:26 - Dependencies required 11:03 - Start of coding after dependencies are done 15:20 - Diagram on MVVM (explanation on MVVM and a bit on MVI) 16:55 - End of explanation on MVVM (and MVI) back to coding 31:58 - End of coding, wrap up and talk about the upcoming courses
@@codingwithmitch No, you are the real MVP for providing us with all this quality free (and quality paid xD) content. I just thought I'd help out some of my fellow learners :)
Thank you Mitch!!! I love your videos. The subject is very interesting and you speak very clearly with an easy to understand explanation. My English is very basic but I can understand everything that speaks perfectly. Thank you so much!
Hey, I love your videos! Just for the record , I do care about the little bits of over information you give such as the description of Gson. Every little bit helps paint a picture when I am trying to determine best practices and important libraries. Thanks for the video.
Mitch thats really fascinating. I dont know when I am goanna go with your all courses. Really good stuffs.!!! And its like day by day new libraries and new architecture are showing up. Got so many things to learn man!!! I wish one day i will complete all your courses.
Great video Mitch. One quick note (apologies if people already pointed this out): hashCode is not the object address/reference in memory (unless you didn't override it, in which case, it's default implementation actually is - Kotlin overrides hashCode() for data classes). hashCode() returns hash value of the fields of the instance of the class; in fact, by design, two instances of the same class with the same field values should hash to the same hash code or "equals" wouldn't work. What you are looking for is System.identityHashCode(Object) -- docs.oracle.com/javase/6/docs/api/java/lang/System.html#identityHashCode%28java.lang.Object%29
Instead of putting cancelJobs function into onDestroyed wouldn't it be better if we put it into onCleared in viewModel ? Thanks for the great tutorial.
As always amazing video and great explanations. Quick question: Isnt that way to set LiveData in the Repository a little bit weird? Wouldnt you normally use methods like postValue for that? I've never seen this done like that in Java so I am confused why it is done like this in Kotlin. Thanks in advance.
In the documentation it says that the instance of a Singleton is created the first time you uses it; So, is not created right when you declare it, and this implicitly means that it is lazy initialization. Therefore, isn't redundant to initialize the Singleton by lazy?
Your videos would be THE best video if you could teach us to use the design patterns in different scenarios like, login logout session, filling and submitting forms, network check and load content for placeholder, recyclerview with actions, etc
The viewModelScope is bounded to ViewModel’s lifecycle. It has created to automatically handle cancellation when the ViewModel’s onClear() is called. So if we are going to use that I think we don't need the viewModel.cancelJobs(), Right?
Loving the work you do, thanks. Just a suggestion. You should cancel jobs on the ViewModel onCleared method. It triggers when activity destroyed, basically same thing you do on activity onDestroy method.
First of all Thank you for the video! I will become a member as soon as possible. I have a question, What if my getUser method needs two parameters? What can I do?
In ApiService, you can change function return type from User to Response and inside Repository set value = user.body, before that you can check if user.isSuccessfull() and also you can wrap the whole thing inside try/catch for exception,
HI, for some reason when I initialize job = Job() I get build errors , no matter how many time I try android studio calls it Unresolved , what might be the issue?
Yeah you can handle with coroutines. If there's an error just return an error state. ex: github.com/mitchtabian/Open-API-Android-App/blob/master/app/src/main/java/com/codingwithmitch/openapi/ui/DataState.kt. If you want to see examples watch this course: codingwithmitch.com/courses/powerful-android-apps-with-jetpack-architecture/
Hey Hi Mitch, I really love the way you explain the things... So can you please help us on how to handle network errors like 'No Internet', response with error code 404,500 etc in CoroutineScope... currently I am getting below error FATAL EXCEPTION: DefaultDispatcher-worker-2 retrofit2.HttpException: HTTP 404 Not Found
great video but why in Repository.kt you used this method override fun onActive() {} why you not use liveData{} block and emit() function and why in viewmodel you not use Repository as DI thanx
this is really great thanks. however one thing - how can/do we pass an error message back to the UI using this pattern ? eg. the Retrofit API call fails for whatever reason. can you add this to the example ?
That's what the powerful android apps course is for. Showing you a more detailed use case. There will be an offline cache, error handling, everything you need. codingwithmitch.com/courses/powerful-android-apps-with-jetpack-architecture/
shouldn't the co routine be written in viewmodel coroutine scope so that when activity or fragment gets destroyed the coroutine gets cancelled automatically but in your case the network repository coroutine is still running or waiting for the data?? may be i am wrong
I prefer to do it in the repository because I like to create a new job for each event. If I canceled the ViewModelScope it would cancel all jobs instead of just the single event.
Thank you, it is very helpful. Can you show the error handling with this example like 404 or No Internet connection and Progress loader, so that it will a complete solution? waiting for the tutorial.
Hi Mitch: i have one question in callback what is mean this part "Code that heavily uses callbacks can become hard to read and harder to reason about" developer.android.com/courses/extras/multithreading#callbacks
Hi Mitch your tutorial is very awesome i will subscribe in you website asap but i need to ask you about if u are using usecase pattern or not and koin for DI and TTD Thank you again for awesome explanation
@@codingwithmitch You can see this article and you will understand me “Android clean architecture with ViewModel, UseCases and Repositories: Part 1” by Antoni Castejón García proandroiddev.com/android-clean-architecture-with-viewmodel-usecases-and-repositories-part-1-b9e63889a1aa
What will happen when you call another getUser while previous is not completed? Don't you should call job.cancel() in the beginning of Repository.getUser?
Actually I missunderstood what you were asking. You don't need to because of the switchmap. The unique properties of a switchmap ensure only one observable is emitted at any given time. So if you searched again it would be terminated already through the switchmap.
Discord channel. But it's for members only. codingwithmitch.com/enroll/ With a membership you get access to all my courses and offline downloads codingwithmitch.com/courses/
I like your video's very much, but hashCode is NOT a memory address in any way. For that you will have to do something like sun.misc.Unsafe.getAddress(..)
You are giving a bad example of using singletons everywhere. I guess it's just to show that they exist, but you forgot to mention how bad it will be fot testing everything when only singletons are used. And in Repository.kt if you call getUser twice, you will be able to cancel only last job since you overwrite your job variable. And simple fix like canceling job before rewriting it won't work either cuz u may use this function all over your app and it's not ok to expect it not to work sometimes. This place need some refactoring. A guess this is, again, for demonstration purposes but the devil is in the details. You had to at least mentioned it. Apart from those small but very important details, great vid.
CodingWithMitch , please have a look what does "hashCode" really mean, how it is generated and then eventually use it to prove your theories. As in your example the hashcode is the same. before and after the rotation, because of the properties of the singleton object not because of the address of the singleton in the memory. Please edit your video, so the people that are going to watch the video, won't be misguided. Good luck :)
@@codingwithmitch hashcode is generated based on the values of the object members. For example if you create another singleton object with the same object property values, the hashcode would be the same. The rule is that objects with equal property values have the same hashcode,and that's why if you'd like to have equals working you have to have equal hashcodes for the objects you are comparing.
@@slavromanov1637 Interesting. Thanks for clearing that up. Just to make sure I understand correctly. Consider this example: I have a singleton POJO with two string parameters. If I set the two string parameters to some values (call them "val1" and "val2"). Then do a config change or however you want to force the object to be destroyed. If I create another singleton and set the values to the exact same ("val1" and "val2"), it will have the same hashcode?
Hello Mitch I am new to your videos. Can you possibly sometime do video on viewmodelscope available in androidx.lifecycle:lifecycle-viewmodel-ktx:2.1.0?
I don't think this is the best approach to use Singletons with LiveData. your LiveData from repository is always creating a new Singleton Object. Kinda defeats the purpose
@@codingwithmitch No, it is not. your method always returns a newly created singleton. try asking someone else for a 2nd opinion if you don't believe me
Yes it still returns the same instance. Use this code for the Repository and MainActivity and look at the log output for the hashcode of the ApiService. It's the same location in memory. gist.github.com/mitchtabian/f7e152b0ca2881e5238a96f8177f7eca
Just revisited this video, and rewatched and found the very same issues. I am referring to the object created in Repository.kt that is returned by the `getUser(userId: String)` method. It is always a new object. An object is only considered a singleton, when it is nested in a class, not as an inner object but just as an object or when it is a top level object. Constructing an anonymous object (regardless it extends another class/entity), wont return a singleton. Also, class properties that are assigned to objects (anonymous or not) will always have a different addresses for different instances of the class To prove my point, try calling Repository.getUser(userId: String) twice, you will realize that the two instances are different and they are from different memory addresses as well. Although, they will probably serve the same content but as I said earlier, it does defeat the purpose
you saved my life man! thank you soo much
this is perfect i understood everything, you're such a great teacher!!!
i'm gonna be recommending memberships for your website to _EVERYONE_
Lot of respect for you sir! I want to switch to Kotlin and try to find some good tutorials. I must say no one is better than you in android here on UA-cam! Thank you soo much for these videos.
Just like your teaching skill a lot, U r a great teacher, the most imp thing in this video is how you build a repository class...Thanks again for the great stuff.
Your smooth and clear voice is making the tutorial more enjoyable. You're talented 👏
0 Dislikes...That is just evidence of how amazing this video is!
So far
Thanks for taking an effort to teach us in the easiest way.
I'm waiting for your new course, i'm excited to learn MVI architecture
Timestamps:
00:00 - Intro
01:51 - What is a singleton?
04:26 - Practical example of a simple singleton in code
06:09 - Actually writing the singleton class
09:45 - A real, much more practical example
10:26 - Dependencies required
11:03 - Start of coding after dependencies are done
15:20 - Diagram on MVVM (explanation on MVVM and a bit on MVI)
16:55 - End of explanation on MVVM (and MVI) back to coding
31:58 - End of coding, wrap up and talk about the upcoming courses
You the real MVP
@@codingwithmitch No, you are the real MVP for providing us with all this quality free (and quality paid xD) content. I just thought I'd help out some of my fellow learners :)
Thank you Mitch!!!
I love your videos. The subject is very interesting and you speak very clearly with an easy to understand explanation. My English is very basic but I can understand everything that speaks perfectly. Thank you so much!
Hey, I love your videos! Just for the record , I do care about the little bits of over information you give such as the description of Gson. Every little bit helps paint a picture when I am trying to determine best practices and important libraries. Thanks for the video.
Mitch thats really fascinating. I dont know when I am goanna go with your all courses. Really good stuffs.!!! And its like day by day new libraries and new architecture are showing up. Got so many things to learn man!!! I wish one day i will complete all your courses.
Yeah it's tough to keep up
13:18 Yes I absolutely cared about that quick bit of information! It saved me from having to look it up myself!
Amazing tutorial, u are my new favorite channel. Have subcribed and liked,
Keep working hard Mr Mitch :D
Great video Mitch. One quick note (apologies if people already pointed this out): hashCode is not the object address/reference in memory (unless you didn't override it, in which case, it's default implementation actually is - Kotlin overrides hashCode() for data classes). hashCode() returns hash value of the fields of the instance of the class; in fact, by design, two instances of the same class with the same field values should hash to the same hash code or "equals" wouldn't work.
What you are looking for is System.identityHashCode(Object) -- docs.oracle.com/javase/6/docs/api/java/lang/System.html#identityHashCode%28java.lang.Object%29
yeah I gave the incorrect description. Someone already pointed that out. But thanks
Instead of putting cancelJobs function into onDestroyed wouldn't it be better if we put it into onCleared in viewModel ? Thanks for the great tutorial.
As always amazing video and great explanations.
Quick question: Isnt that way to set LiveData in the Repository a little bit weird? Wouldnt you normally use methods like postValue for that? I've never seen this done like that in Java so I am confused why it is done like this in Kotlin. Thanks in advance.
Great job explaining Singletons!
30:32 I think you could've cancel the jobs in the onClear method on viewmodel, that way it would cancel automatically when the activity is destroyed.
In the documentation it says that the instance of a Singleton is created the first time you uses it; So, is not created right when you declare it, and this implicitly means that it is lazy initialization. Therefore, isn't redundant to initialize the Singleton by lazy?
Your videos would be THE best video if you could teach us to use the design patterns in different scenarios like, login logout session, filling and submitting forms, network check and load content for placeholder, recyclerview with actions, etc
Hi Mitch great video... Why you did'nt use moshi..? Instead of Gson
The viewModelScope is bounded to ViewModel’s lifecycle. It has created to automatically handle cancellation when the ViewModel’s onClear() is called. So if we are going to use that I think we don't need the viewModel.cancelJobs(), Right?
Very helpful Mitch, as always
Why don't you execute "Repository.cancelJobs()" in the MainViewModel.onClear() method?
What if I don't use lazy? If I just initialize the variable, what will be the problem?
Loving the work you do, thanks. Just a suggestion. You should cancel jobs on the ViewModel onCleared method. It triggers when activity destroyed, basically same thing you do on activity onDestroy method.
Great video 👍 one question is if Retrofit already runs in background thread, why use coroutines?
Looks nicer and more control over what's happening.
to avoid callback hell
First of all Thank you for the video! I will become a member as soon as possible.
I have a question, What if my getUser method needs two parameters? What can I do?
Hi, I'm developer from India. I'm wondering that, how do I handle retrofit errors by following this code?
I am also looking for the same...
TL;DR : Put it in a try catch block.
Check kotlin coroutine 101 from Android developers channel to learn more.
In ApiService, you can change function return type from User to Response and inside Repository set value = user.body, before that you can check if user.isSuccessfull() and also you can wrap the whole thing inside try/catch for exception,
HI, for some reason when I initialize job = Job() I get build errors , no matter how many time I try android studio calls it Unresolved , what might be the issue?
Very useful Mitch. Thanks a lot.
Hi Mitch,
To handle network related exception do we need to go with Rx or we can handle that through coroutine as well??
Yeah you can handle with coroutines. If there's an error just return an error state. ex: github.com/mitchtabian/Open-API-Android-App/blob/master/app/src/main/java/com/codingwithmitch/openapi/ui/DataState.kt.
If you want to see examples watch this course: codingwithmitch.com/courses/powerful-android-apps-with-jetpack-architecture/
@@codingwithmitch
Great
Thanks a lot :)
Thanks to the author, great video.
@codingwithmitch Tq for the tutorial why can't we use .build() inside retrofitBuilder lazy function it give some error of inline functions
Hey Hi Mitch,
I really love the way you explain the things...
So can you please help us on how to handle network errors like 'No Internet', response with error code 404,500 etc in CoroutineScope...
currently I am getting below error
FATAL EXCEPTION: DefaultDispatcher-worker-2
retrofit2.HttpException: HTTP 404 Not Found
Very good session thanks for c cool video 👌
great video but why in Repository.kt you used this method override fun onActive() {} why you not use liveData{} block and emit() function
and why in viewmodel you not use Repository as DI
thanx
Amazing video, learned so much. Can't wait for more videos, thank you for making it!
Very nice content!!! Lots of thing in single video great!! Thanks #YouRock
I needed that One. Thanks Mitch
Awesome tutorial mitch
When are you planning to release your next course on your website?
The MVI course prob in 1-2 weeks then the powerful android apps course
This time I noticed Kodein written on the board in the back. Any plans on making videos on that?
Ya eventually. Not sure when tho
Is it a good practice to use live data in repository for a very large code base app
I wouldn't use live data in a repository at all. Suspend functions are the way
Can you create a full course on Retrofit with Put, Patch and delete functions?
I have lots codingwithmitch.com/courses/powerful-android-apps-with-jetpack-architecture/
34:53 definitely me lol
come back here from MVI course for practice more about kotlin to keep up with the course.
this is really great thanks. however one thing - how can/do we pass an error message back to the UI using this pattern ? eg. the Retrofit API call fails for whatever reason. can you add this to the example ?
That's what the powerful android apps course is for. Showing you a more detailed use case. There will be an offline cache, error handling, everything you need. codingwithmitch.com/courses/powerful-android-apps-with-jetpack-architecture/
Thanks Mitch. This video is very helpful for me
What if we have an error? For example, no internet connection. This case our app will crash
How do you handle retrofit chain calls with coroutine ?
shouldn't the co routine be written in viewmodel coroutine scope so that when activity or fragment gets destroyed the coroutine gets cancelled automatically but in your case the network repository coroutine is still running or waiting for the data?? may be i am wrong
You could use the viewmodelscope. I've been putting the job in the repository.
Great video Mitch. Can you please make a video about MVI architecture. Thanks a lot!
Yep I will
@@codingwithmitch Please we need one more MVI architecture using coroutines + retrofit. Thanks.
@@aks4125 I got a course brother codingwithmitch.com/courses/model-view-intent-mvi-architecture/
You could as well override OnColeared on the ViewModel to call cancel jobs
Hi Mitch,
Awesome turorial as always ...
Could ie be possible to make a tutorial about unidirectional data flow as a best practice ?
What is @Expose for?
Thank you! your video is easy to understand
Really your awesome sir
Can't we cancel job in viewmodelScope like
override fun onCleared() {
//
I prefer to do it in the repository because I like to create a new job for each event. If I canceled the ViewModelScope it would cancel all jobs instead of just the single event.
Mitch you are love.
thanks love you too bro
thanks, here is your comment for the youtube algoritm
Lol thanks
Thank you, it is very helpful. Can you show the error handling with this example like 404 or No Internet connection and Progress loader, so that it will a complete solution? waiting for the tutorial.
Y it's right here man codingwithmitch.com/courses/model-view-intent-mvi-architecture/
The other courses I have are also complete solutions
Hi Mitch:
i have one question
in callback what is mean this part
"Code that heavily uses callbacks can become hard to read and harder to reason about"
developer.android.com/courses/extras/multithreading#callbacks
Awesome tutorial!
Hi Mitch
your tutorial is very awesome i will subscribe in you website asap
but i need to ask you about if u are using usecase pattern or not and koin for DI and TTD
Thank you again for awesome explanation
I don't know what usecase pattern is
@@codingwithmitch
You can see this article and you will understand me
“Android clean architecture with ViewModel, UseCases and Repositories: Part 1” by Antoni Castejón García proandroiddev.com/android-clean-architecture-with-viewmodel-usecases-and-repositories-part-1-b9e63889a1aa
Thank you for this awesome tutorial!
How to use retrofit service callback class
What will happen when you call another getUser while previous is not completed? Don't you should call job.cancel() in the beginning of Repository.getUser?
What you would actually want to do is have a job object inside the NetworkBoundResource. That way it's unique to the request
Actually I missunderstood what you were asking. You don't need to because of the switchmap. The unique properties of a switchmap ensure only one observable is emitted at any given time. So if you searched again it would be terminated already through the switchmap.
you know me so well 😙
How can I show and hide progress dialog on api request and response with this example?
By watching my mvi course my friend codingwithmitch.com/courses/model-view-intent-mvi-architecture/
I want to know how to handle 401,404,500 error using kotlin coroutines
You are amazing man... 🙏🙏🙏
Funny things Id 2 will not work 😁😁
Great mitch 👍
Thank you so much!, If I could I doin a lot of likes for you.
Do you have any slack channel where we can ask questions??
Discord channel. But it's for members only. codingwithmitch.com/enroll/
With a membership you get access to all my courses and offline downloads codingwithmitch.com/courses/
Have you got a tutorial with viewModelScope?
Not on that specifically.
Thank you🙏 Dhanyawad
real help man!
Great 36 minutes video. Learn something good.
Awesome. Thank you.
great tutorial 👌
Why mvvm is used only in kotlin, is it not possible for java developent??
yes you can use java or kotlin
Is good to change to Kotlin or to maintain in java in android app development.?
@@kumarraja93 I would switch to kotlin
@@codingwithmitch thank you mitch
Great tutorial!!
How to use coroutine scope in Android service
Amazing
Awesome thanks
Can you make a complete lecture on Room Persistence Library ?? :(
I have a free course codingwithmitch.com/courses/sqlite-room-persistence-android/
@@codingwithmitch Thank You
i don't know why but when i use only IO or Main, it gives an arror. So i have to use Dispatchers.IO
Prob wrong import
I've never seem Room plus Firebase using MVVM structure.
I like your video's very much, but hashCode is NOT a memory address in any way. For that you will have to do something like sun.misc.Unsafe.getAddress(..)
hey mitch i realy like to give u money for course but i dont have: ... WISH i could reach to your member required Courses in your site
I think you should cancel job in ViewModel when onCleared fun called
Should I have separate repositories for each of my view models?
Yes
Thank you
Please make video for kotlin flows
Thanks for it
You are giving a bad example of using singletons everywhere. I guess it's just to show that they exist, but you forgot to mention how bad it will be fot testing everything when only singletons are used.
And in Repository.kt if you call getUser twice, you will be able to cancel only last job since you overwrite your job variable. And simple fix like canceling job before rewriting it won't work either cuz u may use this function all over your app and it's not ok to expect it not to work sometimes. This place need some refactoring. A guess this is, again, for demonstration purposes but the devil is in the details. You had to at least mentioned it.
Apart from those small but very important details, great vid.
CodingWithMitch , please have a look what does "hashCode" really mean, how it is generated and then eventually use it to prove your theories. As in your example the hashcode is the same. before and after the rotation, because of the properties of the singleton object not because of the address of the singleton in the memory. Please edit your video, so the people that are going to watch the video, won't be misguided. Good luck :)
So the hashcode will only change if the properties of the object change? I always thought (new hashcode) = (new object instance)
@@codingwithmitch hashcode is generated based on the values of the object members. For example if you create another singleton object with the same object property values, the hashcode would be the same. The rule is that objects with equal property values have the same hashcode,and that's why if you'd like to have equals working you have to have equal hashcodes for the objects you are comparing.
@@slavromanov1637 Interesting. Thanks for clearing that up. Just to make sure I understand correctly. Consider this example:
I have a singleton POJO with two string parameters. If I set the two string parameters to some values (call them "val1" and "val2"). Then do a config change or however you want to force the object to be destroyed. If I create another singleton and set the values to the exact same ("val1" and "val2"), it will have the same hashcode?
@@codingwithmitch Instead of asking me why don't you check it in the IntelliJ Idea IDE?
@@codingwithmitch Their's hashcodes will be the same.
Hello Mitch
I am new to your videos. Can you possibly sometime do video on viewmodelscope available in androidx.lifecycle:lifecycle-viewmodel-ktx:2.1.0?
Probably. I don't usually use it because I usually do asynchronous work in the repository.
great
I don't think this is the best approach to use Singletons with LiveData. your LiveData from repository is always creating a new Singleton Object. Kinda defeats the purpose
No. It's accessing the Singleton. Not creating a new one.
@@codingwithmitch No, it is not. your method always returns a newly created singleton. try asking someone else for a 2nd opinion if you don't believe me
@@andy_lamax I will check tomorrow
Yes it still returns the same instance. Use this code for the Repository and MainActivity and look at the log output for the hashcode of the ApiService. It's the same location in memory.
gist.github.com/mitchtabian/f7e152b0ca2881e5238a96f8177f7eca
Just revisited this video, and rewatched and found the very same issues. I am referring to the object created in Repository.kt that is returned by the `getUser(userId: String)` method. It is always a new object.
An object is only considered a singleton, when it is nested in a class, not as an inner object but just as an object or when it is a top level object. Constructing an anonymous object (regardless it extends another class/entity), wont return a singleton. Also, class properties that are assigned to objects (anonymous or not) will always have a different addresses for different instances of the class
To prove my point, try calling Repository.getUser(userId: String) twice, you will realize that the two instances are different and they are from different memory addresses as well. Although, they will probably serve the same content but as I said earlier, it does defeat the purpose