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Layouts Overview

View Layouts are a type of View class whose primary purpose is to organize and position other view controls. These layout classes (LinearLayout, RelativeLayout, etc.) are used to display child controls, such as text controls or buttons on the screen.

Android activities (screens) use layouts as a container for view controls, and layouts can actually contain other nested layouts as well. Nearly all Android activities have layout containers similar to the way that most HTML documents use "divs" to contain other content.

There are a few very commonly used layouts and then many more specialized layouts that are used in only very particular cases. The bread and butter layouts are LinearLayout, RelativeLayout, and FrameLayout.

It's important to note the class hierarchy of these View Layouts. Each of them subclass ViewGroup, which itself subclasses View. That means it is perfectly legal to pass a layout such as LinearLayout as an argument for something that takes View as a parameter. ViewGroup also contains the nested static class LayoutParams which is used for creating or editing layouts in code. Keep in mind that each subclass of ViewGroup, such as LinearLayout, has its own nested static class LayoutParams that's a subclass of ViewGroup.LayoutParams. When creating View Layouts in code, beginners will often confuse the many different available LayoutParams classes and run into hard to catch problems.