Develop Reference

Android | ScrollView | height wrap_content

How does Android think about ScrollViews?
I come from webdev background, so that is my paradigm for implementing a scrolling element.
Yet on Android, official tutorials and docs say, I should use height="wrap_content" for the ScrollView. But why?
From my understanding(webdev), ScrollView should be the container, in which it's content scrolls. Meaning ScrollView being the height restriction (therefore match_parent) and it's content should be higher than that (therefore scrolling).
If I set ScrollView height to wrap_content, and Android would actually honor that... it should not be scrollable (by my webdev paradigm) (unless Android does not add additional layout containers (outside those defined in layout file).
So how is it done?

A view group that allows the view hierarchy placed within it to be scrolled. Scroll view may have only one direct child placed within it. To add multiple views within the scroll view, make the direct child you add a view group, for example LinearLayout, and place additional views within that LinearLayout.
Here is a Link that helps you to know more about it
https://developer.android.com/reference/android/widget/ScrollView
and also here
https://www.javatpoint.com/android-scrollview-vertical

What is the point of a FrameLayout for single element

I understand the advantage of a FrameLayout when you need to add multiple children to it. But what is the point of adding a FrameLayout as your root element when you only have one child (lets say a TextView)? I mean why wouldn't you simply set that single child (e.g. the TextView) as the root of your layout?

A FrameLayout is - as the name implies - a Layout. It inherits from ViewGroup which is used for positioning and aligning child views.
Of course you would be able to set a TextView alone in your Layout xml. But what are you going to do if you want it to be centered?
Then it would make sense to use a FrameLayout as a sort of "Wrapper" around your TextView which lets you position it the way you want.

Fragment Transactions with scrollview

You have an Activity A --> display a fragment B (scrollView), on next button you have fragment C replaced with relative Layout. But the view is not replaced.

ScrollView Defines as follows :
"A view group that allows the view hierarchy placed within it to be scrolled. Scroll view may have only one direct child placed within it. To add multiple views within the scroll view, make the direct child you add a view group, for example LinearLayout, and place additional views within that LinearLayout."
-ScrollView is not a base view hence wrapping the scrolling in base views like (Linear Layout,RelativeLayout Can solve your problem

What does child mean in an android layout?

I am new to Android Development, so what is meant by child in the below paragraph....
A ScrollView is a FrameLayout, meaning you should place one child in
it containing the entire contents to scroll; this child may itself be
a layout manager with a complex hierarchy of objects. A child that is
often used is a LinearLayout in a vertical orientation, presenting a
vertical array of top-level items that the user can scroll through.
https://developer.android.com/reference/android/widget/ScrollView.html

In android (and most other technologies), views can have subviews, aka "children". Most views can have children and can be a child of a parent view. It's kind of like a "tree".
The most obvious feature of being a child of some other view is that the child moves with the parent view. Another feature is that the child is in the coordinate space of the parent view.
Your paragraph here basically says you can only put one child view in ScrollView and it is usually a LinearLayout. But don't be fooled! This child can have its own child views.

Gaurav i think this is what you looking for, you need to use only one LinearLayout tag inside ScrollView tag, if you are using more than one LinearLayout than it will show error. If you want to use more LinearLayout tag you can use them inside LinearLayout tag which is inside ScrollView tag. May be this will help you.

You need to understand the general concept of child and parent . Simply you can think of the real life relation between parent and child.on the hierarchy parents are toplevel and child is below.so when you come to android layout parent is container and child is the content.

What are the differences between LinearLayout, RelativeLayout, and AbsoluteLayout?

I am confused about the difference between LinearLayout, RelativeLayout, and AbsoluteLayout.
Could someone please tell me the exact differences between them?

LinearLayout means you can align views one by one (vertically/ horizontally).
RelativeLayout means based on relation of views from its parents and other views.
ConstraintLayout is similar to a RelativeLayout in that it uses relations to position and size widgets, but has additional flexibility and is easier to use in the Layout Editor.
WebView to load html, static or dynamic pages.
FrameLayout to load child one above another, like cards inside a frame, we can place one above another or anywhere inside the frame.
deprecated - AbsoluteLayout means you have to give exact position where the view should be.
For more information, please check this address https://developer.android.com/guide/topics/ui/declaring-layout#CommonLayouts

Definitions:
Frame Layout: This is designed to block out an area on the screen to display a single item.
Linear Layout: A layout that arranges its children in a single column or a single row.
Relative Layout: This layout is a view group that displays child views in relative positions.
Table Layout: A layout that arranges its children into rows and columns.
More Information:
FrameLayout
FrameLayout is designed to block out an area on the screen to display a single item. Generally, FrameLayout should be used to hold a single child view, because it can be difficult to organize child views in a way that's scalable to different screen sizes without the children overlapping each other. You can, however, add multiple children to a FrameLayout and control their position within the FrameLayout by assigning gravity to each child, using the android:layout_gravity attribute.
Child views are drawn in a stack, with the most recently added child on top. The size of the FrameLayout is the size of its largest child (plus padding), visible or not (if the FrameLayout's parent permits).
RelativeLayout
A RelativeLayout is a very powerful utility for designing a user interface because it can eliminate nested view groups and keep your layout hierarchy flat, which improves performance. If you find yourself using several nested LinearLayout groups, you may be able to replace them with a single RelativeLayout.
(Current docs here)
TableLayout
A TableLayout consists of a number of TableRow objects, each defining a row (actually, you can have other children, which will be explained below). TableLayout containers do not display border lines for their rows, columns, or cells. Each row has zero or more cells; each cell can hold one View object. The table has as many columns as the row with the most cells. A table can leave cells empty. Cells can span columns, as they can in HTML.
The width of a column is defined by the row with the widest cell in that column.
Note: Absolute Layout is deprecated.

LinearLayout : A layout that organizes its children into a single horizontal or vertical row. It creates a scrollbar if the length of the window exceeds the length of the screen.It means you can align views one by one (vertically/ horizontally).
RelativeLayout : This enables you to specify the location of child objects relative to each other (child A to the left of child B) or to the parent (aligned to the top of the parent). It is based on relation of views from its parents and other views.
WebView : to load html, static or dynamic pages.
For more information refer this link:http://developer.android.com/guide/topics/ui/layout-objects.html

LinearLayout - In LinearLayout, views are organized either in vertical or horizontal orientation.
RelativeLayout - RelativeLayout is way more complex than LinearLayout, hence provides much more functionalities. Views are placed, as the name suggests, relative to each other.
FrameLayout - It behaves as a single object and its child views are overlapped over each other. FrameLayout takes the size of as per the biggest child element.
Coordinator Layout - This is the most powerful ViewGroup introduced in Android support library. It behaves as FrameLayout and has a lot of functionalities to coordinate amongst its child views, for example, floating button and snackbar, Toolbar with scrollable view.

Great explanation here:
https://www.cuelogic.com/blog/using-framelayout-for-designing-xml-layouts-in-android
LinearLayout arranges elements side by side either horizontally or vertically.
RelativeLayout helps you arrange your UI elements based on specific rules. You can specify rules like: align this to parent’s left edge, place this to the left/right of this elements etc.
AbsoluteLayout is for absolute positioning i.e. you can specify exact co-ordinates where the view should go.
FrameLayout allows placements of views along Z-axis. That means that you can stack your view elements one above the other.