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.
What is the difference between a View and a ViewGroup in Android programming?
View
View objects are the basic building blocks of User Interface(UI) elements in Android.
View is a simple rectangle box which responds to the user's actions.
Examples are EditText, Button, CheckBox etc..
View refers to the android.view.View class, which is the base class of all UI classes.
ViewGroup
ViewGroup is the invisible container. It holds View and ViewGroup
For example, LinearLayout is the ViewGroup that contains Button(View), and other Layouts also.
ViewGroup is the base class for Layouts.
Below image is the answer. Don't take it too complex.
A ViewGroup is a special view that can contain other views (called children.) The view group is the base class for layouts and views containers. This class also defines the ViewGroup.LayoutParams class which serves as the base class for layouts parameters.
View class represents the basic building block for user interface components. A View occupies a rectangular area on the screen and is
responsible for drawing and event handling. View is the base class
for widgets, which are used to create interactive UI components
(buttons, text fields, etc.).
Example : ViewGroup (LinearLayout), View (TextView)
Reference
View is a basic building block of UI (User Interface) in android. A view is a small rectangular box which responds to user inputs. Eg: EditText, Button, CheckBox, etc..
ViewGroup is a invisible container of other views (child views) and other viewgroups. Eg: LinearLayout is a viewgroup which can contain other views in it.
ViewGroup is a special kind of view which is extended from View as its base class. ViewGroup is the base class for layouts.
as name states View is singular and the group of Views is the ViewGroup.
more info:
http://www.herongyang.com/Android/View-ViewGroup-Layout-and-Widget.html
ViewGroup is itself a View that works as a container for other views. It extends the functionality of View class in order to provide efficient ways to layout the child views.
For example, LinearLayout is a ViewGroup that lets you define the orientation in which you want child views to be laid, that's all you need to do and LinearLayout will take care of the rest.
Viewgroup inherits properties of views and does more with other views and viewgroup.
See the Android API: http://developer.android.com/reference/android/view/ViewGroup.html
in ViewGroup you can add some other Views as child. ViewGroup is the base class for layouts and view containers.
View is the SuperClass of All component like TextView, EditText, ListView, etc..
while ViewGroup is Collection of Views(TextView, EditText, ListView, etc..), somewhat like container.
A View object is a component of the user interface (UI) like a button or a text box, and it's also called widget.
A ViewGroup object is a layout, that is, a container of other ViewGroup objects (layouts) and View objects (widgets). It's possible to have a layout inside another layout. It's called nested layout but it can increase the time needed to draw the user interface.
The user interface for an app is built using a hierarchy of ViewGroup and View objects. In Android Studio it is possible to use the Component Tree window to visualise this hierarchy.
The Layout Editor in Android Studio can be used to drag and drop View objects (widgets) in the layout. It simplifies the creation of a layout.
In simple words View is the UI element which we interact with when we use an app,like button,edit text and image etc.View is the child class of Android.view.View
While View group is the container which contains all these views inside it in addition to several othe viewgroups like linear or Frame Layout etc. Example if we design & take the root element as Linear layout now our main layout is linear layout inside it we can take another view group (i.e another Linear layout) & many other views like buttons or textview etc.
A ViewGroup describes the layout of the Views in its group. The two basic examples of ViewGroups are LinearLayout and RelativeLayout. Breaking LinearLayout even further, you can have either Vertical LinearLayout or Horizontal LinearLayout. If you choose Vertical LinearLayout, your Views will stack vertically on your screen. The two most basic examples of Views are TextView and Button. Thus, if you have a ViewGroup of Vertical LinearLayout, your Views (e.g. TextViews and Buttons) would line up vertically down your screen.
When the other posters show nested ViewGroups, what they mean is, for example, one of the rows in my Vertical LinearLayout might actually, at the lower level, be several items arranged horizontally. In that case, I'd have a Horizontal LinearLayout as one of the children of my top level Vertical LinearLayout.
Example of Nested ViewGroups:
Parent ViewGroup = Vertical LinearLayout
Row1: TextView1
Row2: Button1
Row3: Image TextView2 Button2 <-- Horizontal Linear nested in Vertical Linear
Row4: TextView3
Row5: Button3
So I really have two related questions on ViewGroups:
Is a LinearLayout and instance of ViewGroup? Meaning, can I call getChildAt(index) when using a LinearLayout?
Can I detect when a ViewGroup child is at the "top" of the screen (right below the action bar) after scrolling? For example, when the 3rd child is scrolled to the top
I'm working on an app that utilizes Parallax Scrolling and I'm using an open source library that has a custom View with a LinearLayout as a child and 4 TextViews as the LinearLayouts children. In their custom View class they are calling getChildAt but I can't seem to find documentation on that related to LinearLayouts so I wanted to check. And essentially I want to check if one of these TextViews are at the top of the screen. Any clairfication would be much appreciated
question 1 { Is a LinearLayout and instance of ViewGroup? Meaning, can I call getChildAt(index) when using a LinearLayout? }
answer = yes... A ViewGroup is a special view that can contain other views (called children.) The view group is the base class for layouts and views containers .. so your linear layout is a view because it extends view, and if it contains other sub views called children then it's a viewgroup.. viewgroup extends view.. Meaning YES you can call getChildAt(index) when using linear layout..
question 2 { Can I detect when a ViewGroup child is at the "top" of the screen (right below the action bar)? }.
answer YES , you can check the Z order of the children in a viewgroup(a view containing other sub views) to know its position, so probably your first child is the child below the actionbar, that's if your viewgroup (that is the linear layout) is the view content of your activity - which is always the case right? - yea..
if you want a documentation on getChildAt and viewgroups in general then look here ..
hope it helps.. let me know anything that's arising..
What is the difference between a view and a subview in Android?
there is no such thing called a 'subview', its just used to refer to a view inside another view.
View is the base class for widgets, which are used to create interactive UI components (buttons, text fields, etc.). and if we insert a view inside the another the its become Subview like a linear Layout containing a button view, here button is a subview
Like Vinay said, there is no such a thing. But you have ViewGroup that contains other Views. For example, LinearLayout, RelativeLayout etc are derived from that class.
If you wish, you can read more about it here:
http://developer.android.com/reference/android/view/ViewGroup.html
I understand that View overlapping has been addressed for background images with components on top. However, what if I had the following, where the image from a button overlaps another view, outside of its container?
Example 1
View are not allowed to overlapped in LinearLayouts. It is used to arange child views in either vertical or horizontal manner. When views are bigger than its parent, it renders in the bounds of its parent and the rest is cut of.
You can stack child views on top of each other by using the framelayout. But from seeing your buttun, I think you can achieve it using a Relative layout. And telling the arrow to stay below button using layout_below attribute.