Develop Reference

Is there a quick and easy way to preview a layout at different screen sizes?

Is there a quick and easy way to see how my application will look on different screen sizes and shapes? Currently, I'm going into the AVD manager, editing my device definition, and then launching a fresh emulator. It takes maybe ten minutes for each one.
They layout is defined entirely from resource files. I don't actually need to execute the app. Is there a faster way to do this?
Edit: I should add: there are some custom widgets in the app.

While looking at a layout open the "Design" tab or open the "Preview" tab on the side. On the top of the window you will see a list where you can change the layout and orientation.

May not solve your entire issue, but it's a good to know.
If you want to have a preview of a static page (not rendered at runtime, like recyclerview), you could use android studio to do that.

Is it possible to customize the BottomNavBar without Icons, Change the text and Changing the selected tab background

BottomBarNavigationBar template
BottomBarNavigationBar
Note : It should follow google material design guidelines also.

Removing Bottom Navigation Bar is not possible in non-rooted android device. But you can set buttons to just above the Bottom navigation Bar,it would work fine and look nice.
For changing text style you can go through this link. It would clear your doubt.
Changing the selected tab is definitely possible. For this go through this link
And finally I am sorry that I am giving just link here, as all the questions you asked are already available on SO.
So please, next time when you ask any question, then do a detail research about it then post that here.

Creating a circular tab host in android

Firstly, I would like to mention that since i am not sure of the terminology of the view that i am looking for so I shall try and explain the behaviour.
I am looking for build a screen with multiple tabs where the tab indicators do not fit all inside the screen so it is scrollable. This is fine but i want that when the scrolling happens, after the last tab indicator, the tab widget automatically shows the first tab indicator right after it. So kind of like a circular tab widget.
Could someone please give pointers on how this could be achieved in android.
Thanks,
Sunny

I'm not sure, since you're not so clear...but i think you're looking for this:
https://github.com/astuetz/PagerSlidingTabStrip
Sliding tabs like the ones in Google Play.

setting my main project default to linear instead of relative

Everytime I follow a tutorial book or you tube video, I have also used the cheat help in eclipse. My programming always comes out with errors. here is one example why does all the tutorials main activity comes out showing linear layout and my projects default is relative layout. So how do I change the default to linear when creating new project.
I know I can open a new layout xml but all the tutorials opens a new project in linear.
I am a massive fan of android and I really want to make some apps, but all the tutorials never seem to correspond with the results I get and they all make it look so easy.

go to youre layout.xml
make sure to be in the graphical layout (check bottom bar)
top-right in 'outline' right-click on the relative layout
choose 'change layout'
choose youre desired layout, (linearlayout(vertical) probably in ur case)

I found it after digging a lot in Android Studio After visiting JetBrains and Intelij documentation and help sections i found nothing much helpful but i found way on my own, I had answered it here, With all explanation and screenshots.

Android Custom TabBar

I have seen a couple of application having a TabBar like the following here. I am talking about the widget the bottom left hand corner of the image. You can drag the circular disc and change the tab. Also an Image POP ups about the current TAB. I have tried searching about but so far no luck.
Kind Regards

This is something that HTC developed for their own usage.
it is not available openly to developers sorry.
If you want something like this you will need to develop it on your own.
You can achieve this by using a TabHost widget with TabWidget placed in a horizontal scroll view and then on tab click show some kind of custom fullscreen Toast message with the description and the image. also customize the TabWidget, you can definitely find info on the Tabhost and customizing the tabwidget either here on stackoverflow or some tutorials on google.
In any case you definitely need to do this from scratch, but its certainly possible.