What is the difference between a View and widget in Android?

Question

What is the difference between a View and widget in Android?

Answer 1

As is stated in the View class docs:

This 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.).

The ViewGroup subclass is the base class for layouts, which are invisible containers that hold other Views (or other ViewGroups) and define their layout properties.

Therefore a View is a base class for UI elements and a Widget is loosely defined as any ready to use View.

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Let's emphasize these concepts a little more.

View

A View is a base class for all UI elements. It, therefore, covers many different classes and concepts, including widgets, ViewGroups and layouts. There is a root View attached to a Window instance which forms the basis of the View hierarchy. In general, the word View is usually used to describe UI elements in general, or to refer to abstract or base UI classes such as ViewGroups.

Widget

There are various definitions for this term, but most refer to a "ready to use" UI element, be it a Button, ImageView, EditText, etc. Note that some people consider widgets to be UI elements that are complete (not abstract) and are not containers (such as ViewGroups (layouts/ListViews)). It's also worth noting that "widget" is a package name (android.widget) where the docs mention the following:

The widget package contains (mostly visual) UI elements to use on your Application screen.

Therefore, it is reasonable to consider non-visual UI elements to also be widgets, as well as any class defined under the widget package. See here for a full list of classes in the widget package: http://developer.android.com/reference/android/widget/package-summary.html

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App Widget

Not to be confused with a UI element widget, an App Widget is a remote View hierarchy which is most commonly displayed on the user's home screen. As defined by the docs:

App Widgets are miniature application views that can be embedded in other applications (such as the Home screen) and receive periodic updates. These views are referred to as Widgets in the user interface, and you can publish one with an App Widget provider. An application component that is able to hold other App Widgets is called an App Widget host.

ViewGroup

A ViewGroup is a subclass of View and provides the ability to parent and position child Views, such as in the case of Layouts.

Layout/View Containers

Much as with Widgets, there is no Layout base class, therefore it could be loosely defined as any class which extends ViewGroup and provides the ability to define the positioning of child Views within it. Usually, only ViewGroup subclasses which are appended with the word "Layout" (as in LinearLayout, RelativeLayout) are referred to as "layouts", other classes extending ViewGroup are usually just referred to as "view containers".

Finally, I'd like to suggest that whenever you mention Views, widgets or any other important term, to make it clear your intended definition so that people can better understand what you're referring to.

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Further Reading

• What is the difference between Views and widgets?

Answer 2

A Widget is a View. A Layout is a ViewGroup. To create a widget, you extend a View.

Answer 3

I had your same confusion about it, above all for the two packages android.view and android.widget. I ended up thinking of widgets as "ready to use" views, and views as just elements to build widgets. If I make a custom view that will be directly used in a layout, I would consider that a widget.

Answer 4

Just some quotation from "The Busy Coder's Guide to Android Development", Ch 6:

All widgets, including the ones shown above, extend View, and as such give all widgets an array of useful properties and methods beyond those already described.

Answer 5

Views are concerned with layouts, placeholders.

Widgets are concerned with data, UI behaviors (ex Sliders). Views contain widgets.

Answer 6

I don't believe any of the earlier answers are really correct. Different UI toolkits use different terminology for what is often essentially the same thing, and it is true that an Android View is pretty similar to a .NET Control or a Qt widget.

But "widget" also means something very specific in Android. If you long press on the home screen, you get an "Add to home screen" dialog that offers to add Widgets (among other things). If you touch the Widgets line, you get a menu of widgets like Analog Clock 1 through 4.

According to developer.android.com/guide/topics/appwidgets, these are special entities that lets your process display content in another process's View. Like the home screen. There is a special broadcast protocol that you inherit for free, but you also interact with the Views in your developer.android.com/reference/android/widget/RemoteViews.html host via a special protocol that appears to involve marshaling. I have just started to look into writing one (which is how I found this question) but the docs do say that you can only use FrameLayout, LinearLayout, and RelativeLayout layouts, and that they can only contain AnalogClock, Button, Chronometer, ImageButton, ImageView, ProgressBar',TextView, andViewFlipper` "widget classes" - "Descendants of these classes are not supported."

This is just a bit restrictive!