Singleton vs Transient - What's the Difference in .NET Dependency Injection?

Singleton... Transient... When should you use what when building client apps and web apps with .NET? Registering your dependencies correctly has import implications when it comes to lifecycle events and how you users will interact with your application. I break down what you need to know.
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Chapters:
00:00 - Introduction
00:30 - What is the dependency injection service?
01:36 - What is a singleton dependency?
02:20 - What is a transient dependency?
03:00 - Demo app walkthrough
04:20 - Singleton View, Singleton ViewModel
04:50 - Transient View, Singleton ViewModel
05:50 - Transient View, Transient ViewModel
06:30 - Singleton View, Transient ViewModel
07:50 - Wrap-up & thoughts
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#dependencyinjection #dotnet #dotnetmaui #aspnetcore

[@JamesMontemagno]

Want to learn about Scoped dependencies? Checkout my followup! kzbin.info/www/bejne/fn6xY2mthp19a5Y

[@bkaankose]

Simple explanation James, thank you! One thing to note here is that (since it may not be clear with View-ViewModel example), avoid injecting transient into singletons. Because the object you define as 'short living or stateless' is now living in an object you define as 'global'. Your transient will live inside this singleton for the whole application lifetime and it may create thread safety issues.

[@vickyfikriachri2311]

Thank for the video James. Super helpful.

[@jewersp]

Great video. Nothing new to me, but it's great to actually see the differences in this way, it helps and confirms existing practices.

[@faranahmadk7401]

Excellent. It cleared all the doubts. Thanks James.

[@candidodmv]

Congrats James as always is comming awesome content!

[@lindomagaye8729]

Thanks for such a great explanation, James. Since I started following you I'm learning a lot!

[@kopilkaiser8991]

Shared, subscribed, and liked. You deserve it. All of it brother. Best wishes to you for your progression and may you excel to your very best.

[@MotherOfTony]

very good explanation of dependency injection, thank you james!

[@rikudouensof]

Will add this in next weeked side project.

[@sam14032]

Thanks ! Very easy to understand and super interesting.

[@yeica]

Finally an example without GUIDs, thank you

[@4Asteria]

Very clear to the point. Thank you very much for your effort

[@Namco78]

Very good explanation, thank you for clarifying this. Great example, astonishing app 🙂

[@christianzaragoza7575]

Que gran maestro James, te felicito por la excelencia de tus tutoriales

[@hwod44]

Great explanation. You could talk about STATIC variables inside Transient injections too. Thx James

[@DavidDanosTech]

Smooth. Nice!!!!

[@JamesMontemagno]

Thanks!

[@breula]

Awesome! In the last example where the page was defined as single and model as transient if cliqued on increase button certainly the number goes from 5 to 1. James should have done this.

[@PierreBritoM]

Amazing explanation!

[@michael_azzer]

Amazing explanation 👌

[@mojoojoseph8145]

Very concise.😁

[@codingdave]

Great video @james. When would you use scope in a WPF/MAUI application? Maybe when you open a file the application can work on?

[@JamesMontemagno]

Never, for web apps only docs.microsoft.com/en-us/dotnet/core/extensions/dependency-injection#scoped

[@letsdoit7630]

Thanks for the explanation. I am used to c# windows application designs and familiar with binding the UI with a database like SQL or mySQL directly or via background code, but am struggling to understand the structure when it comes to MVVM and .net MAUI and linking to a hosted sql DB. I would appreciate if this is something you could give your opinion about. Thanks for the good content.

[@jamesleonmiller4504]

Thanks for explanation, James. Nice video. I am curios, what is practical difference between Get() and Resolve() when using introduced in Xamarin Forms, DependencyService?

[@amnshumansunil3371]

Hi James can you please make a video on unit testing

[@sheilainglin863]

AWESOME 👌 🆒️ 🙌 👍👍👍😁

[@mattrobb3566]

Thanks James. Was Using Maui for Windows App. Was using Transient for a Page which used Events (Events were enabled on appearing and disabled on disappearing). But noticed that the previously used transient Pages remained in memory and their event triggers triggered events in the New Page, so after leaving and returning to this page 3 or 4 times I was receiving 3 or 4 events when I should have received one!! Indicating the transient pages are remaining in memory! By switching the ViewModel and the the Page to Singletons this issue disappeared as would be expected. What I didn't understand is when transient pages are no longer being used why are they retained in memory?

[@BJBEAR989]

Great explanation of singleton and transient. What would you recommend in order to handle Android screen rotations in Maui? When using Xamarin a screen rotation caused the activity to be recreated which effectively destroyed the data in the view. I suppose my real question is does Maui preserve the contents of the view when the screen is rotated?

[@JamesMontemagno]

It preserves the screen state automatically. Android does by default now

[@bernhardtarmann1254]

Thanks James! I really understand Singeltons and Transients but I’ve got problems with the third type. What’s the secret of the Scoped instances?

[@JamesMontemagno]

Gotta wait until next week to find out tehehehe

[@oktjona]

can you do a video on how to connect netmaui app to sqlserver

[@michaelrogers6935]

So when you register a class with a dependency injection service, and somewhere in the app an instance is being instantiated, does it automatically consult the service to see if there's an object? And does that apply to *any* object that's being created? And is the dependency injection service just storing the objects to be injected (the dependencies) or does it also store the objects that will be the recipients of the dependencies? So, if MainPage depends on a View Model, do you need to store both the Main Page and View Model, or just the View Model? [I feel like I am soooo close to understanding this 😀

[@sakabas28]

JamesMontemagno => GEMSMontemagno ♥

[@aslanamca8225]

Hello, I want to ask something I'm curious about. I create an instance of another class in a service registered as a singleton, with its new keyword. There will be only one instance of the singleton service within the application, but it will create another class inside it each time it is called. For example, if it is called 100 times, it will create 100 class instances. The last sample can be used but what about the previous 99 samples? Does the garbage collector detect and clean them or is this a memory leak issue? It's not the lifetime of the service I'm wondering about, it's what will be the class instances created in the singleton service.

[@sfuentesojeda]

how do I get back to a previous page but when a button is clicked?

[@dfmf1982]

Hi James do you have a course in Udemy?

[@amrosalah01]

does Xamarin packages still work with Maui ? things like Macha for background tasks for example

[@JamesMontemagno]

Some may be backwards compatible and some may to be updated, it depends on the package. On nuget you can see if it targets net6 then you know it is updated

[@AdamsTaiwan]

Still to early in the day for me to get this. What I've been doing lately is creating ViewModels that function as services. I instance them using a script and keep the instance reference in a Dictionary. Every instance contains a GetView(string name) which can return any bound named view and a Process(string command) which allows me to script the object.

[@HackelSchorsch]

Transient pages loaded from the shell do not behave transient. This is a bug which is already open for months.

[@pablomontesmorquecho5388]

Have you find any workaround to this?

[@gwisekor]

6:40 어렵지만 중요한 내용. 난 그냥 new를 쓰고 싶다. ㅎㅎ

[@knockout4907]

Is Singleton per user or global for everyone?

[@JamesMontemagno]

Singleton will return the same instance when requested.

[@FabioGomesCG]

And AddScooped ?

[@JamesMontemagno]

For web projects only really docs.microsoft.com/en-us/dotnet/core/extensions/dependency-injection#scoped

[@kishant4565]

Need to create a pdf / printable page like receipt printing /barcode stickers printing using .Net Maui, please help.

[@JasonPurkiss]

just fyi when I want to create pdf's in Xamarin I open a web page from the app and send the app data to the web page and then save as pdf, a lot simpler, let me know if you find a better and cheaper way :) as not the fastest and easiest solution :( I tried all the other solution's on the net but couldn't get on with any of them

[@NK-xw4uu]

By "request" do you mean a http request or do you mean request for an object?