Develop Reference

Is there a way to add Xamarin.forms to a Universal Windows App(UWP)?

I have a UWP application and I want it to be able to run into Android and also IOS using Xamarin.forms. Is there anyway to port it and run it on both of them?

Short answer: no.
Long answer: Xamarin Forms is "Xaml" too, but works on top of a completly different framework.
If you have used a good architecture, you can use all your viewmodels (or whatever your ui logic is called) and just put a Xamarin.Forms UI on top of that. With a little luck, you can reuse a lot of the structure from your existing xaml, but as most names are different, it is almost a complete rewrite. Or you could put a native UI with Xamarin.Plattform UI on top of your code.
So if you want to go cross platt form, you have to add at least one completely new UI.

Android - App with layouts only - without controllers

I'm programming an app in Android.
My client needs a 'dummy' like application, I mean, an app with all layouts but just navigable, without the actual controllers or activities, just navigate through layouts. By clicking buttons, but just pass to the other layouts without executing java or whatever code.
My question is, is this possible in AndroidStudio?
Or should I generate another kind of graphical app in order to accomplish this?
Any ideas?
Thanks in advance!

The short answer to your question (as I understood it) is no. You have to have activities to have an android app that will function. You could create a very rudimentary set of activities to do what you want.
However, if you are simply trying to create a mockup of what the app will look like for your client, I suggest using a tool like FluidUI. This will allow you to layout the general look and feel of your app without any actual code required.
Let me know if this helps!

Multi Window App Development

I want to develop an android application which has to run two other applications on the device with one app on upper half of the screen and the other in lower half of the screen. Any clues/suggestions to start developing this ? Thanks in advance !

it's not possible multi-pane-layout two other apps.
if u want your app with multiple activities follow this tutorials for your references:
it's called named as multi-pane-layouts and offical introduction about multi-pane-layouts below link:
http://developer.android.com/design/patterns/multi-pane-layouts.html
and it's shows how to implement multi-pane-layouts on your project below link from android official side:
http://developer.android.com/guide/practices/tablets-and-handsets.html
and you can download example project from github below link:
https://github.com/faisalgeek/MultiPaneAndroidApp

This is not possible, except via custom device firmware or ROM mods. In standard Android, only one app can be used at a time.
However:
You are welcome to support multi-window apps on some Samsung devices, as they have extended their firmware to support this concept
You are welcome to have an activity's theme set up to not fill the screen, though anything else around the activity will at most be visible and will not respond to touch events
If all of these applications are yours, combine them into one app, and then you can display elements of that app alongside other elements of that app however you wish.

If you are looking for a feature for your app which supports multi-window then Latest Android version N has a new cool feature called Multi-window support, you can let your app support multi-window which can be resized and scaled which is exactly your requirement. you can find the reference link here

mobile multiplatform development with native UI

i have developed an app, running on iphone and android, using phonegap and jquery mobile.
The combination of them is really great.
To support multi platform, I have also evaluated some other platforms too, but the problem that i have is that the UI does not feel native (and although not a problem for most apps performance cannot be compared with native).
The only solution so far giving acces to native UI seems to be monotouch.
Do you have any suggestions on platforms offering native ui at least on iphone and android, regardless of language used?
Thanks.

The only way to have native UI response is to write native apps.

The native UI is a puzzle indeed. You need read HIG firstly, cook UI with color and images to get close with system default ones. But if you are using PhoneGap thing, why do you even worry about it? Just rely on framework to get close the look and feel. Get your app really useful is more attractive than looking accustomed for user.
But it is important to adjust interactive design to avoid conflict. For example iOS navigation bar has return button in left most part, don't put it at right. And Android user will get disappoint if there is no response for long pressing or context menu key pressing.

for now i will go with a mixed on js based on phonegap and native controls plugin which i will extend as needed.

Is there Android Intent concept in iPhone SDK

Just switching from Android to iPhone. In Android I can make several apps and use a tabView to call each app as intent.
In iPhone, I can make several apps. I need a tab to call each apps or app views. Is there similar concept as intent in iPhone? Just switched to iPhone, copying all the other projects into the tabbar does not work out. If you have other methods to solve, I really appreciate. Thanks,

Android and iOS are very different in this regard. Android is very open about letting you use intents to mix and match activities from other apps. iOS isn't like that; each app runs in its own private space and generally cannot even see other apps' data, let alone use their services. It is possible to cause other apps to run via custom URLs, but that's not the same thing.
What you'll need to do is to copy or move the code for the view controllers, views, etc. of your various iOS apps into your tab bar app project. You'll build them all into a single application, and the tab bar will switch between the view controllers.

With iOS 8 you will have something similar to Android Intents. Using App Extensions you can reach similar behavior.
In a close future Apps will start expose their "extension" (as you do in Android Framework declaring Intent Filters in the manifest) that will be used by application who need.The extension areas allowed in this first version are:
Today
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Action
Foto Editing
Document Provider
Custom Keyboard
It's great finally apple release this functionality!

Intent in Android covers a lot of functions. There is no iOS equivalent to that.
But if your objective is to launch a different app, and pass parameters to it, you can try out URL Schema.
Let's say you have app AAA with URL schema aaa:// and app BBB with URL bbb://
You can launch app AAA, and call bbb://v=1&c=2 for example, to launch BBB and get the parameters. you can even take these parameters to control what view to show, so you can have a similar concept in Android, to call different Activity with Intents.
You have to register URL schema in Info.plist

The closest concept to an Intent on iOS is the handling of certain URLs by the system applications. See here. It was possible to register your own application URL schemes at one point (see this article), but I must admit I haven't tried this in recent SDKs (IIRC Glympse links can be opened in the Glympse app, so this technique probably still works).

As of 2016, Apple has added an Intents framework that is similar to Android's, albeit much more restrictive. Expect Apple to add more Intents in the future, but for now it is quite limited. https://developer.apple.com/reference/intents

Since iOS 8, you can use App Extensions.