Develop Reference

Implement camera lib with Kotlin multiplatform

I'm trying to understand what structure should have a multiplatform library. Checking on the Internet I've seen a huge number of examples explaining how to make a log or a "hello world" but there's a lack of complex examples, even in the official documentation (important to note that I'm only interested in mobile platform, iOS and Android).
So I want to create an example that simply opens the camera (as a lib, not as a multiplatform app) just to have an idea of how to work with a real feature which, also, is native. Right now I have created a project following the official example, so it has a common module (using expect) and one for Android and one for iOS (using actual), and now these are my doubts:
I've seen that the iOS module is also in Kotlin, Kotlin/Native as I understand. Should my project have also an wrapper in Swift, or will the library have no Swift code? And if it should, where should it be in the project structure?
Also in the Android module I've noticed I cannot import the class "Activity" nor the "Intent", which I will need to open the camera, why? is this code restricted to Java without the Android libs? Should it also have a wrapper to Android? If so, how can I configure this wrappers?
I know I can use the "expect" key when creating classes but, as I understand, the common and the native modules will always be separated classes. I mean, if I create a class in the common module, can I define methods of this class using "expect" and define them later in the native?
Can my lib have a Manifest?
Finally, does anyone knows a real example that really explain a more complex situation?
Thanks

Okay, let's go through your questions one-by-one.
I would recommend you to have a look at this example
The
iOS module produces an Objective-C framework as a result. It can be utilized by the Xcode project the same way as any other framework with non-Kotlin origins.
It looks like the unavailability to use
Android SDK is the result of using jvm("android") target instead
of android() one. To use the android target, one has to apply the android Gradle plugin in addition to kotlin-multiplatform one.
I
think you want to do something like that: just ordinary class
declaration in the common and extension function for it with an
expect modifier. And then actualize it in the platform-specific
code.
I think so.
I'd also recommend you to have a look at
this and this, maybe these examples will be complex enough for you.😁

NativeScript : Use platform specific native library without a multi-platform plugin?

We're trying to use ArcGIS's Android Runtime SDK in NativeScript (it has no nativescript plugin) but we have accessed that rewriting the whole library as a multi-platform plugin would take too much time.
My question is, how can we utilize the native library directly but only the android version of it?
This is the library: https://developers.arcgis.com/android/latest/api-reference/reference/packages.html
Also, is it possible to use it without a custom UI plugin? I don't understand how to add the mapView to the app .xml
For example, in their AndroidStudio tutorial they mention the following steps and I'm not sure how to translate them to NativeScript
Source : https://developers.arcgis.com/android/latest/guide/develop-your-first-map-app.htm

I'm not quite sure what you mean by re-writing the whole library, you never have to do that.
Plugins are being written to wrap the native library with simple user friendly JS api / methods, it necessarily need not to be cross (or multi) platform either.
You may even directly access any third party library within your project as soon you mark them as dependency in your app gradle file.
Here is how you access native apis.
For instance if you want to create an instance of LocatorTask, this should work once you add the library as dependency in your NativeScript project.
const locatorTask = com.esri.arcgisruntime.tasks.geocode.LocatorTask("URI_HERE");
locatorTask.loadAsync();

Is it possible to compile a Xamarin project as a library for iOS and Android?

I need to create an API library for Android and iOS. I have experience working with Android projects, but zero experties in iOS. I was wondering if I could create a Project library in Xamarin that compiles as a JAR for Android and as an... I-don't-know-which-type for iOS.

No, that isn't possible. Depending on what you are trying to accomplish there may be alternatives. If you are trying to make a library that can be used by others you could make it a Xamarin component - there is a component store you could put it on if you want it to be generally available, otherwise you can use any normal means of source or object distribution.
If you need to interact with a native app/library then you could make the C# code the "owner" of it and have it call into the native code. This works for both IOs and Android (and is used to work with e.g the play services from google).

No, it is unfortunately not possible to do that.

It seems to me that what you need is a Portable Class Library also known as PCL. It allows you to create a project which can be referenced by all Xamarin supported platforms (such as iOs and Android). There are obviously limitations to the approach like not being able to reference platform specific libraries but in your case (of writing an API) it should suffice.
You can read more in this link
Good Luck!

"Library projects" in iOS

Some time ago I created and Android app. Then I needed to create very similar app (functionality-wise) with some cosmetic, branding and small-scale functionality changes. I refactored the original app as a library project, created an app that used this library project and recreated the original functionality. Then I created a new app that used that same library project and also implemented the small-scale changes required for the second app. This worked perfectly fine. Now if a change is needed, it's very easy to implemented it in multiple apps: I just change the library project and recompile all the apps.
I also had the original application available for iOS - and need to make the second app available for iOS. I could, naturally, copy the project, make the changes and create another apps. However this would mean double work if I needed to change something in the core functionality. I'd like to be able to refactor the iOS project/app similarly to the Android one, but not sure how to go about it - or if such functionality is even available. Any suggestions are much appreciated.

You can create a Single project with differents targets.
Then, you will have target A, and B for example and CoreFile files that are common for all targets.
Let's suppose you have HomeViewController with some slightly differences.
You can create a single interface HomeViewController.h and two implementation AHomeViewController and BHomeViewController, both extending BaseViewController.
Then open AHomeViewController, and on FileInspector at 'Target Membership' mark only target A. On BHomeViewController you do the same. Image 1, illustrate what you have to do (names are differents from the example because it's a real example from one of my projects).
If for some reason you have need to know what's targets are you using you can define it using Preprocessor Macros on Target -> Build Settings. As illustrate by Image 2.
Then you can use #ifdef APP_CB to check the current target.

As was mentioned you can really regulate target membership[About] of every file which you add. But in my opinion is better to create a separate framework(library) and add it as dependency
[Swift consumer -> Swift dynamic framework]

Are there Android compatible alternatives to Property Utils?

Is there a handy-dandy equivalent to org.apache.commons.beanutils.PropertyUtils on Android?
I can't seem to use bean utils in my android app due to some dependencies on PropertyDescriptor,and IndexedPropertyDescriptor. So I'm wondering if there are any alternatives?
Basically all I want to do is use a method name as a string "someMethod" and feed that into setMethod(anObject, "someMethod", value), much like PropertyUtils does; but without having to resort to the nasties of reflection...
Or are my hands tied and I need to use Reflection?

There is bridge library which works on Android: android-java-air-bridge.jar. Just include into project path and use all apache beanutils features in your Android project as you could use in ordinary java application. Moreover, there are lot of other classes which moved to this Android supporting library. Look at the list.

There is a possibilty to use libraries or write own code depending on the PropertyUtils. But it sure isn't dandy. You can get the general idea about what has to be done in this thread.
There are apparently some projects who have successfully solved the issue, so you can study thier solution. Take a look at Drawingpad-base and libgdx. You can find PropertyUtils in the package com.madrobot.beans in the first project and com.badlogic.gdx.beans in the second.