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What are the pros and cons of android data-binding?

Both of my colleague and I have experience in MVVM of Web App, while we are new to native android development. Now we have contrary opinions about android data-binding -- I'm a fan of it while he is not.
My Arguments:
Reduces boilerplate code which in turns brings
Less coupling
Stronger readability
Powerful, easy to implement custom attribute and custom view
Even faster than findViewById (details)
His Arguments:
The auto-generated .class increases app size.
Harder to debug
I've made some investigation but there are not many discussions about it. Now I want to collect the pros and cons of android data-binding.
Aspects of discussion include but are not limited to:
unit test
app size
performance
learning curve
readability
coupling

I will comment on your arguments first then I will state my opinion:
1.Remove boilerplate code - it will remove some it will just move some in the xml or it will require additional classes. So you have to be careful and balance the use of data binding.
2.Stronger readability - depends if you are a new developer then you may find it easy to learn it but if you previously worked on android you will need extra time to learn it.
3.Powerful - the code has more power, you can implement whatever you like in code. Think about it like this, everything you implement using data binding has a code equivalent (it might be longer and more code to write), but the revers is not valid.
4.Even faster than findViewById - comparing the speed between these two, in my opinion is useless, you will never notice the difference, if you see some difference, then one of the implementation is wrong.
5.Auto generated class - it's true it will increase the app size, but again only if you have tons of it it will matter. It's true that on the android dev web site they state that it's kind of bad to use libraries that create autogenerated code or annotations that will generate extra code.
6.Hard to debug - depends, like readability, of what you are used to, heck debugging is hard either way for some problems, and you will get better by debugging not by using a different library.
So this is pure my opinion, I've developed many apps using different libraries and different approaches, and they all had pros and cons, but what I've learn: balance everything, don't use tons of libraries, don't waste time implementing things that are implemented already and work well, don't "decouple everything", don't "couple" everything, don't use code only, don't try to "generate" everything.
I think it's quite wrong, and you can get a wrong idea, if you ask for 'pros & cons' about some library/implementation, because usually it won't be impartial, you will get a lot of pros from somebody who used the library in a specific way and it worked and others will give you cons because they used different and it didn't work.
So in conclusion, I think you should check what the library can do for you and what can't do for you and decide if it's good for your setup. In other words, you should decide if a library is good for you not other people ;).
Update - 8 August 2018
First of all I still stand with my initial conclusion, balance is the key in these kind of situations, but in my case, data-binding speed-up a little bit the development process and also improved it. Here are a few new points that you should all think about.
Testing the UI -- with data-binding it's much more easy to test the UI, but data-binding it's not enough for that, you also need a good architecture and using the Google suggested architecture will show the actual power of data-binding.
The most visible changes were provided for points 2 & 5 from my original answer. It kind of was easier to read the code after we decided to use data-binding, and the most important thing here is: we as a team decided that we will use data-binding and after that, we kind of expected to have most of the trivial and basic UI setup in the XML file.
For the debugging part, here's a little bit tricky, Android Studio has a lot to improve on the errors and autocomplete for the data-binding but the most common errors you'll get them after the first 2-3 occurrences. Also I've learned that a "clean project" form time to time, helps A LOT.
Another point that you'll have to take in consideration is the project configuration to use data-binding, right now AS (3.1) supports by default data-binding (just set a flag in graddle) for Java, but I had some issues with Kotlin, after a bit of search here on SO, I managed to fix everything.
As a second conclusion (from my original post), if you can and the project deadline/requirements/etc allows you to try data-binding, go for it it will worth (unless you do some really stupid stuff :)) ).

I am working on a huge Android project and the team has decided to phase out Data Binding library. Why? The primary reason is that it is exacerbating build time(10+ mins), by generating a lot of classes in the build process.

Even if i like danypata's answer i would like to add/edit some of his statements to android databinding.
1.Remove boilerplate code - As written in danypatas answer it removes some code and adds some code somewhere else like in layouts. That doesnt mean that the boilercode isnt reduced because usually it is reduced.
For example you may want to create a bindingadapter, which handles several custom arrayadapters for your spinner/recyclerview/listview/.. but requires only one simple adapter. You may want to use the adapter in your layout by using e.g.
app:myCoolAdaptersData="#{model.mydata}"
Now you can create your generic adapter and (re)use your bindingadapter in all your layouts instead of using for example:
ListView lv = findViewById(...);
CoolGenericAdapter<MyModel> coolAdapter = new CoolGenericAdapter<>(...);
lv.setAdapter(coolAdapter);
This is just one simple example which recudes the code alot in larger projects. Another sample to recude code is, that you bind your model to your layout. Updating field-values of your model usually updates your model aswell (if its at least a BaseObservable/ObservableField).
That means that you dont need to find all your views, update your views, update your models, ...
2.Stronger readability - The extra time spent for learning databinding doesnt really matter. Since the layouts are not really different except that you wrap them into a layout tag and put your namespaces there, it doesnt really differs from "regular" layouts. Using bindingadapters and accessing the model in the layout may take some time, but usually you can start beginning with the basics which are easy and beautiful to use aswell. Learning new stuff always takes time, but you will easy overhaul the time when using databinding after a while.
3.Powerful - Yes, its very powerful. Its easier to reuse existing code, reuse existing bindingadapters and may lead to more generated code but thats not always true. For example you may create multiple adapters within several classes instead of creating one bindingadapter, it may be hard to "optimize" it later. Optimizing the Bindingadapter means that it gets updated everywhere. Optimizing may decrease the "lines of code" since the boilerplace is reduced anyway.
I agree to 4. and 5.
6. Hard to Debug Since AS 3.0+ outputs useful hints like syntax issues in your layout (line number and file) its easy to debug databinding generated code. If you have problems finding the issue you may also want to check for errors in the generated code. Some librarys like dagger 2 or android architecture library may confuse you because the error lines doesnt match with the real "error". This is due generated code by other annotation processors. If you know that those annotation processors may get in trouble with databindings error outputs, you can easy fix that.
7. Unit Testing Its possible like if you dont use databinding by using executePendingBindings.
8. Readability Readability may be better without databinding. Since you put some business logic into your layout, some into your real code, it may lead to spaghetti-code. Another problem is that using lambdas in your layout may be very confused if the "layout-designer" doesnt know which param may be used.
Another very big problem is that bindingadapter can be everywhere. Using BindingAdapter annotation generates the code. That means that using this in your layout may lead to problems to find the proper code. If you want to update a bindingadapter you need to "find" it.
When should you use what? For larger projects it is a really good idea to use databinding together with the mvvm or mvp pattern. This is a really clean solution and very easy to extend. If you just want to create a small simple application you'r fine using MVC Pattern without databinding. If you have existing generic bindingadapters which can be used from other projects you may want to use databinding, because its easy to reuse this code.

Data binding, concept wise looks promising to me, but I do not like the implementation part.
I would appreciate a bit more simpler and direct approach to it.
Thus I feel lot more comfortable in keeping it old school.
Model classes, mutable objects, observers feel like too much to me, if some how the data variables used for binding are received as Objects that are mutable and observable directly in a class , then that would make the process lot more cleaner, simpler and concise.

Trying to fit a "clean architecture" on an iOS app

Recently I’ve been rethinking my android architecture project, trying to adapt it to a more “clean architecture”, specifically, the kind of design suggested by “Uncle Bob”.
Which it involves several layers of abstractions, a nice isolation of responsibilities and a very strong dependency inversion achieved by dependency injection; which, ultimately, leads to a very decoupled-portable system. A perfect candidate to be tested by unit testing and integration testing.
In my android implementation I’ve ended up having three different modules or layers:
-domain: entities, interactors, presenters (pure java module)
-data: (acts as a repository to supply the data to the domain) (android library module)
-presentation: ui related stuff, fragments, activities, views, etc (android application module)
So, I’m trying to figure out what would be the best approach on the iOS ecosystem.
I’ve tried creating a project with multiple targets to achieve the same solution:
-domain: command line target (which seems very weird but I think is the most pure swift target available)
-data: cocoa touch framework
-presentation: cocoa touch framework
With this approach I can use these targets in the way I did with android modules. But the first caveat I’ve found it is that I need to add manually every new file to the dependent target.
But my knowledge is very limited in projects with multiple targets. I mean I’ve never created an iOS application with multiple targets. So I don’t know even if the solution would be use a framework (cocoa touch/cocoa) as a target instead of a command line module for the domain layer.
Any thought would be really appreciate.
Thanks!

Uncle Bob's Clean Architecture absolutely applies to iOS, Swift, and Obj-C. Architecture is language agnostic. Uncle Bob himself codes mostly in Java but in his talks he rarely mentions Java. All his slides do not even show any code. It is an architecture meant to be applied to any project.
Why am I so sure? Because I've studied MVC, MVVM, ReactiveCocoa, and Clean Architecture for 2 years. I like Clean Architecture the best, by far. I tested it by converting 7 Apple sample projects to using the Clean Architecture. I've used this approach exclusively for over a year. It works out better every time.
Some of the benefits are:
Find and fix bugs faster and easier.
Extract business logic from view controllers into interactors.
Extract presentation logic from view controllers into presenters.
Change existing behaviors with confidence with fast and maintainable unit tests.
Write shorter methods with single responsibility.
Decouple class dependencies with clear established boundaries.
We also added a router component so we can use multiple storyboards. No more conflicts.
Writing unit tests is greatly simplified too because I only need to test the methods at the boundaries. I don't need to test private methods. On top of that, I didn't even need any mocking framework because writing your own mocks and stubs becomes trivial.
I've written my experience for my last 2 years studying iOS architecture at Clean Swift I also put together some Xcode templates to generate all the Clean Architecture components to save a ton of time.
UPDATE - To answer #Víctor Albertos's question about dependency injection in the comment below.
This is a really great question and demands a long detailed answer.
Always keep the VIP cycle in mind. In this case, the doSomethingOnLoad() method is not a boundary method. Rather, it is an internal method invoked only within CreateOrderViewController. In unit testing, we test a unit's expected behavior. We give inputs, observe outputs, then compare the outputs with our expectations.
Yes, I could have made doSomethingOnLoad() a private method. But I chose not to. One of the goals of Swift is to make it easy for developers to write code. All the boundary methods are already listed in the input and output protocols. There is really no need to litter the class with extraneous private modifiers.
Now, we do need to test this behavior of "The CreateOrderViewController should do something on load with this request data" somehow, right? How do we test this if we can't invoke doSomethingOnLoad() because it is a private method? You call viewDidLoad(). The viewDidLoad() method is a boundary method. Which boundary? The boundary between the user and view controller! The user did something to the device to make it load another screen. So how do we invoke viewDidLoad() then? You do it like this:
let bundle = NSBundle(forClass: self.dynamicType)
let storyboard = UIStoryboard(name: "Main", bundle: bundle)
let createOrderViewController = storyboard.instantiateViewControllerWithIdentifier("CreateOrderViewController") as! CreateOrderViewController
let view = createOrderViewController.view
Simply calling the createOrderViewController.view property will cause viewDidLoad() to be invoked. I learned this trick a long time ago from someone. But Natasha The Robot also recently mentioned it too.
When we decide what to test, it is very important to only test the boundary methods. If we test every method of a class, the tests become extremely fragile. Every change we make to the code will break many, many tests. A lot of people give up because of this.
Or, think about it this way. When you ask how to mock CreateOrderRequest, first ask if doSomethingOnLoad() is a boundary method that you should write test for. If not, what is? The boundary method is actually viewDidLoad() in this case. The input is "when this view loads." The output is "call this method with this request object."
This is another benefit of using Clean Swift. All your boundary methods are listed at the top of the file under explicitly named protocols CreateOrderViewControllerInput and CreateOrderViewControllerOutput. You don't need to look elsewhere!
Think about what happens if you were to test doSomethingOnLoad(). You mock the request object, then assert that it equals to your expected request object. You are mocking something and comparing it. It's like assert(1, 1) instead of var a=1; assert(a, 1). What's the point? Too many tests. Too fragile.
Now, there is a time when you do mock CreateOrderRequest. After you've verified the correct CreateOrderRequest can be generated by the view controller component. When you test CreateOrderInteractor's doSomething() boundary method, you then mock CreateOrderRequest using interface dependency injection.
In short, unit testing is not about testing every unit of a class. It is about testing the class as a unit.
It is a mindset shift.
Hope that helps!
I have 3 series of draft posts in Wordpress on different topics:
In-depth look at each of the Clean Swift components
How to break up complex business logic into workers and service objects.
Writing tests in Clean Swift iOS architecture
Which one of these do you want to hear more first? Should I bump up the series on testing?

In my opinion Clean Architecture is a set of ideas, rules, principles... to make a code better.
[Android Clean Architecture]
With this approach I can use these targets in the way I did with android modules.
You are able create a target[About](application target or framework target...) but it depends on your needs
If you read Architecting Android...Reloaded from Fernando Cejas
you might have seen that I used android modules for representing each layer involved in the architecture.
A recurring question in discussions was: Why? The answer is simple… Wrong technical decision
The idea is that is not necessary to use some build components to implement Clean Architecture

Protection from reflection - android

Even a private member/function of my class can be accessed by reflection by using setAccessible(true). Is there a way to prevent this kind of access from outside code?
I read something, here on stack-overflow, that I can use SecurityManager for prevention of reflection in applets(not sure how it works, though), but is there a similar mechanism for Android as well? Maybe an annotation or clever-programming?

Taking a step back, what you're observing is a difference in security philosophy, between the Java execution model as originally embodied in JVMs at Sun and the execution model of Android.
The original Java VM design was intended for a system wherein multiple, mutually-suspicious applications (or "applets" in the Java parlance) would simultaneously inhabit a single address space, running in a single VM. Because the designers didn't want one app to be able to mess with another, they went through great pains to define an intra-VM security model that would disallow things such as one object touching the private fields of another object of a different class.
That said, the Java library ended up having various "escape hatches" out of the security model. One of those is setAccessible() on reflection objects, as you note.
Android's model is different: Android uses processes as the security boundary and unit of application isolation, instead of trying to insinuate it into the process as was done with traditional JVMs. This renders moot the entirety of the Java security model, except in that it helps an application "save it from itself." That is, it's good design to not have an object poke into another object's private parts, and the default Java security model provides just that.
Leaving aside the question of people modifying your code, with Android, as an application author, you control all the code that ends up running inside the process of your app. If you choose to include code that calls setAccessible() that's your business. You might be shooting yourself in the foot, but you certainly won't be shooting any other apps' feet, since the Android security model, running as it as at the layer of processes, inherently doesn't let that happen. Likewise, using native code will totally break you out of the Java object model, which allows for the possibility of things going totally higgledy-piggledy in the process but also allows you to express some things in a more productive manner than you could in Java. It's a trade-off, but it's a per-application-developer tradeoff and not one that particularly impacts anything else that's happening on your phone / device.
I know this doesn't directly answer your question, but I hope it provided some useful context.

Is there a way to prevent this kind of access from outside code?
Not really.
is there a similar mechanism for Android as well?
Even if there is (and I am not aware that such a thing exists), anyone can remove it, by decompiling your code (assuming they do not have your source already), getting rid of the protection, and recompiling the code.
Bear in mind that ProGuard, when used properly, will obfuscate your private classes and methods for your production APK builds. That, plus a lack of documentation, will make it tedious for anyone to gain access to those private classes and methods.

I don't believe that you can ever really 100% protect from users using reflection on your project with malicious intent. You can make it more difficult for users to do it by doing things like obfuscating your code, but it is still possible to reflect on the obfuscated code.
I don't believe SecurityManager can be used for the purpose that you are suggesting, though I could be wrong.

Model-View-Presenter and Android Application Design

The Problem: Really large and convoluted Activity classes. Hard to read/understand and modify. Hard to test.
The Possible Solution: Model-View-Presenter (perhaps with dependency injection).
And Mock Test Objects!
I'm planning on implementing Model-View-Presenter in my Android application.
This is basically a variant of the Model-View-Controller. In essence, make the Activity
a glorified layout manager and defer any business logic to the Presenter. Another way of looking at the Presenter is that its like an Helper class instantiated within an Activity to do the heavy lifting with the activity providing a interface/callback that the Presenter can use.
I would like to get some community thoughts on this. For example:
What interfaces are implied by this?
What responsibilities would the Model and View have vs. the Presenter.
For Presenter I suppose the Activity would implement the interfaces needed by the Presenter?
What kinds of things should go into the Presenter vs. Activity?
Would a presenter be one-to-one with an Activity? What about an Activity with multiple fragments displaying different widgets each with its own adapter? Do we now need multiple presenters or still just one?
What about Presenter vs. Adapter?
How should a presenter relate to say an Activity with a ListView and a ListViewAdapter?
What goes into the Presenter vs. Adapter?
Should the Presenter pick the Adapter to use? Or should the Activity make this decision?
Should the Presenter process Model Data or the Adapter? Is there a conflict between adapters and presenters? Are adapters presenters? or something less/more. Usually Adapters are just for widgets like ListViews within an Activity. They don't make the calls that get the data itself I think.
So in model-view-presenter the key thing is really to decides what goes in the presenter vs. other classes and what the communication should be between the presenter and activities, adapters and views/including fragments.
Is Model-View-Presenter just a really bad idea for Android? Or does it fit well with the Android Framework?
Keep in mind there are numerous examples outside Android of very mature SDK's that still needed a micro-architecture like MVP. In fact examples abound: eg. Flex was very mature SDK for Flash and yet it still needed MVP and MVC frameworks for almost any major app.
EJB needed Spring to simplify and organize it. MFC/Struts etc and the list goes on and on. Why should Android be any different? Why should we assume the SDK has everything needed in the case of Android without a design pattern like MVP?
Nice to know before I spend hundreds of hours on this, please feel free to comment/answer on any part of this question.

Android punishes poor MV(P|C) design more than any platform I've ever encountered. Forget the clumsy methods it provides for passing state up and down the activity stack. Get as much state and logic out of your activities as possible. Move it into Services, ContentProviders, and SharedPreferences as appropriate. Try to make your activities pure view. IMO, Services have never been given enough attention in Android tutorials. Even the O'Reilly Programming Android book only gives them a quarter page!
Be wary of extending Application. If you ever start a Service in its own process (e.g., to allow it to be shut down gracefully when an Activity crashes) then the Service will have its own copy of your Application.

Just to provide a reference for others who may be interested. I was thinking the same thing some years before. When we apply MVC/MVVM/Presentation Model to android app, what we really want is to have a clear structured project and more importantly easier for unit tests. At the moment, without an third party framework, you usually have lots of code(like addXXListener(), findViewById()...), which does not add any business value. What's more, you have to run android unit tests instead of normal JUnit tests, which take ages to run and make unit tests somewhat impractical. For these reasons, some years ago we started an open source project RoboBinding - A data-binding Presentation Model framework for the Android platform. RoboBinding helps you write UI code that is easier to read, test and maintain. RoboBinding removes the need of unneccessary code like addXXListener or so, and shifts UI logic to Presentation Model, which is a pojo and can be tested via normal JUnit tests. RoboBinding itself comes with more than 300 JUnit tests to ensure its quality. Other alternatives: Android-Binding, Bindroid and MvvmCross.

Why are many Android API classes non-final, even though they are not explicitly documented for inheritance?

Effective Java (Joshua Bloch) Item 17 says :
"Design and Document or inheritance or else prohibit it"
However, just a cursory glance through the Android APIs reveals that most of the API classes are non-final; which is OK if they are also documented for inheritance (View of Activity, for example). But there are also several non-final classes, but the documentation makes no mention about the inheritability of these classes. Just some arbitrary examples to illustrate my point:
The classes representing the System Services (WifiManager, NotificationManager ...)
Utility classes like UriMatcher.
Some hardware-specific classes like Camera.
Openness and extensibility being the philosophy of Android, is the convention reversed here? Meaning, could one assume that all of the Android API classes are designed to be inherited (whether explicitly documented or otherwise); unless declared final?

Just my €0,02: Clean OO design by the book is one thing, making things work for all possible use cases in practice is another. The principles of clean OO design sometimes are somewhat of academic nature. - And maybe a little bit of black and white.
Think for instance about who uses the Android API provided by google: It's not only app developers but also device manufacturers who need to specialize general APIs for their devices.
So, for me, SW design is neither black nor white in most cases; the shades of grey are important.
And finally: In practice I have seldom (read: never) seen problems caused by "carelessly" omitted final keywords (on classes), while unreflected overuse of final (often caused by thoughts like "my code is sooo [great | ugly], no one will actually ever want to modify it through inheritance") can be quite a pain.
"I know that I know nothing" seems to fit here: It is presumptuous to claim that one knows all the crazy, ingenious, creative, smart,... ideas of others for how one's code may be used in the future beforehand.

The Android developers went to great lengths to ensure that extensibility, while not recommended in many cases, is possible. The motivation behind this appears to be related to testing environments.
For instance, it would be much more difficult to create a faux WifiManager for the purposes of creating unit tests if it were finalized. Without the finalization, it is trivial to subclass the WifiManager (e.g. to mimic "unexpected" wifi disconnection during operation) and return an instance of this subclass from a customized testing Context.
So while you will probably never find a reason to implement a subclass of the these classes in an application that you ship to the end users, the flexibility is there to allow you to extend them if it is necessary for one reason or another.
In the case of utility classes, the answer is simply that the utility of the class is not diminished by allowing the developer to subclass; in many cases, a developer can achieve more understandable code reuse by inheritance than by aggregation and delegation.