Introduction to Guide On Android Layouts
The Activity class offers a core collection of six callbacks for handling transitions between stages of the activity lifecycle: (onCreate), (onStart), (onResume), (onPause), (onStop), (and (onDestroy); as an activity enters a new state, the system invokes each of these callbacks.
Figure 1. A simplified illustration of the activity lifecycle.
The system calls methods to dismantle the activity as the user starts quitting the activity. This dismantling is only partial in certain cases; the operation remains in memory (such as when the user moves to another app), so it can also come back to the foreground.
If the user returns to that activity, it resumes the activity from where the user left off. The likelihood of the system killing a given process — along with the activities in it — depends on the activity status at the time.
Memory operation status and ejection provide more information about the relationship between state and susceptibility to ejection.
You probably do not need to implement all the lifecycle methods, depending on the complexity of your activity. It is crucial, though; that you understand each other and enforce those that make sure your app behaves the way users expect.
App Manifest Overview
- Every software project has to have an AndroidManifest.xml file at the root of the project source set (with precisely that name). The manifest file outlines important details for the Android development software, the Android operating system, and Google Play for your project.
- The manifest file is expected to declare the following amongst several other things:
- • Package name of the app, which usually matches the namespace of your code. Android build tools use this to decide where application entities are located when constructing your project. When the application is packaged, the build tools substitute this value with the application ID from The app’s modules that cover all operations, services, broadcast receivers, and content providers. That part may define basic properties such as its Kotlin class name or Java class name. It can also announce capabilities such as which system configurations it can manage, and filters of purpose that explain how to start the component.
- • The permissions the device needs to access secure machine sections or other applications. This also specifies any permissions other applications need to have if they wish to access content from this program.
- • The hardware and software specifications that the application needs, influencing which devices can access the Google Play app.
Android Layouts Complete Guide
A layout determines the user interface structure of your app for example in an operation. All elements within the model are built using the View and ViewGroup objects hierarchy.
A View usually sketches something with which the user can see and communicate. Whereas a ViewGroup is an invisible container specifying the layout structure for View and other objects in the ViewGroup, as shown in Figure 1
The View objects are generally referred to as “widgets,” and maybe one of several subclasses such as Button or TextView. Typically, the ViewGroup objects are called “layouts” and maybe one of several types that have a particular layout structure, like LinearLayout or ConstraintLayout.
A layout that arranges certain views in a single column, either horizontally or vertically in a single row.
A layout that organizes its children into a single vertical or horizontal band. This produces a scrollbar if the window length is greater than the screen length.
Allows you to specify the location of child objects relative to each other (child A to child B’s left) or to the parent (aligned to the parent’s top).
RelativeLayout is a group of views, which display views of children in relative positions. The location of either view may be defined either as relative to the sibling elements (such as the left-of or below another view) or as relative to the parent RelativeLayout area (such as aligned to the center, left, or center.
RelativeLayout lets views of the child determine their location relative to the view of the parent or to each other (specified by ID). Therefore, by the right border, you can align two elements, or make one below another, centered in the screen, centered left, etc.
Both child views are drawn at the top-left of the layout by default, so you have to determine the location of each view using the different layout properties available from RelativeLayout. LayoutParams.
The value for each layout property is either a Boolean to require a layout location relative to the parent RelativeLayout, or an ID to refer to another view in the layout to which the view should be placed
Displays web pages.
FrameLayout is designed to block out a single object region on the screen. In general, FrameLayout should be used to hold a single view of the child, since it can be difficult to organize child views in a way that can be scaled to different screen sizes without the children overlapping.
However, by assigning gravity to each child, you can add multiple children to a FrameLayout and monitor their location within the FrameLayout, using the attribute android: layout gravity.
Android GridView is a ViewGroup that shows objects in a scrollable, two-dimensional grid.CoreGridView interface is one of Android’s most popular configurations.
GridView is mainly useful if we want to view data in grid form, such as images or icons. This layout can be used to construct applications such as image viewer, audio, or video player to display elements in grid form In general, GridView elements are not predefined and the data can be inserted into the layout using
Adapters such as ListAdapter.
A LayoutManager is responsible for calculating and arranging views of objects within a RecyclerView and deciding the strategy for recycling views of objects that are no longer available to users. A RecyclerView can be used by modifying the LayoutManager to enforce a regular vertically scrolling chart, a uniform grid, staggered grids, collections that scroll horizontally and more. A variety of stock model managers is made available for general use.
A LayoutManager is responsible for calculating and arranging views of objects within a RecyclerView and deciding the strategy for recycling views of objects that are no longer available to users.
A RecyclerView can be used by modifying the LayoutManager to enforce a regular vertically scrolling chart, a uniform grid, staggered grids, collections that scroll horizontally, and more. A variety of stock model managers is made available for general use
Android ListView is a view that groups many items and shows them in a scrollable vertical list. The list items are inserted into the list automatically using an Adapter that extracts content from a source, such as an array or database.
In reality, an adapter bridges between UI components and the data source which fills data into the UI component. The adapter keeps the data and transfers the data to the view of the adapter, the view takes the data from the view of the adapter and shows the data on different views such as spinner, view of the chart, view of the grid, etc.
The ListView and GridView are AdapterView subclasses and can be filled in by binding them to an Adapter, which retrieves data from an external source and creates a View representing each data entry
A ConstraintLayout is a ViewGroup that helps you to flexibly place and scale the widgets. ConstraintLayout is available as a software library starting with API level 9 (Gingerbread) that you can use on Android systems.
There are currently various types of constraints that you can use:
- Relative positioning
- Centering positioning
- Circular positioning
- Visibility behavior
- Dimension constraints
- Virtual Helpers objects
One of the basic building blocks of layout formation in ConstraintLayout is relative positioning. These constraints allow you to place a given widget in relation to another. Along the horizontal and vertical axis, you can constrain a widget:
- Horizontal Axis: Sides of left, right, start and finish
- Vertical Axis: top, bottom, and foundation text
The general principle is to restrict a given side of a widget to a different side of some other widget.
For example, to place button B on the right-hand side of button A (Fig . 1):
AppBarLayout is a vertical LinearLayout that is usually the first child inside a CoordinatorLayout and in most cases serves as a wrapper for the ToolBar.
Use the ToolBar as a CoordinatorLayout direct child will work fine but it would not be able to communicate with other child views present. This is where AppBarLayout’s value comes in. Using the parameter, it allows child views to achieve the desired scrolling behavior.
AppBarLayout is a vertical LinearLayout that is usually the first child inside a CoordinatorLayout and serves as a ToolBar wrapper in most instances.
Using the ToolBar as a direct child CoordinatorLayout would work well but it will not interact with other child views present. It is here where the meaning of AppBarLayout comes in. It helps the child views to achieve the desired scrolling behavior by using the parameter.
Further android related best facts: 5 Apps That Help You To Customize Your Android Phones
DrawerLayout acts as a window content top-level container that allows interactive “drawer” views to be pulled out from one or both vertical edges of the window.
Drawer positioning and layout is managed using the android: layout gravity attribute on child views corresponding to which side of the view you want the drawer to emerge from left or right (or start/end on platform versions supporting layout direction) Note that for each vertical edge of the window, you can only have one drawer view. When the model configures more than one drawer view per vertical edge of the window, then a runtime exception will be thrown.
Place your primary content view as the first child with match parent width and height, and no layout gravity > to use a DrawerLayout. After viewing the main content, add drawers as child views, and set the layout gravity appropriately. For heights with a set width, drawers usually use match parent
Navigation Drawer is the sliding menu with a hamburger menu icon in the ActionBar, which appears on the android screen. Building it requires placing multiple views inside the DrawerLayout navigation portion.
A ViewGroup is a special view that can hold other views (called kids) the view group is the container base class for templates and views. This class also describes class ViewGroup. LayoutParams that serves as the base class for parameters for layouts.
Containers, as the name itself implies, hold together objects and widgets, depending on which specific items are required and in what specific arrangement is desired. Containers can, for example, carry labels, fields, buttons or even containers for children. Containers used to organize the layout
The Android platform takes advantage of the user-based protection provided by Linux to identify and isolate app resources. This isolates apps from one another, protecting apps and the system against malicious apps. To do this, Android assigns each Android application a unique User ID (UID) and runs it in its own process.
Android uses this UID to set up an Application Sandbox at the kernel level. The kernel enforces process-level security between apps and the system through standard Linux facilities, such as app-assigned user and group IDs.
Apps cannot communicate with each other by default and have restricted access to the OS. For instance, if application A attempts to do something illegal, such as reading data from application B or dialing the phone without authorization (which is a different program), then the operating system protects against this action because program A does not have the user rights that are necessary.
The sandbox is simple, auditable, and based on a user separation of processes and file permissions in decades-old UNIX-style.
Because the Application Sandbox is in the kernel, this protection model applies to native code and software on the operating system. Within the Application Sandbox, all the software above the kernel, such as operating system libraries, application framework, application runtime, and any applications run. Platforms to enforce security, developers are limited to a particular development system, set of APIs, or language.
.The Android Application Sandbox that isolates data from your device and executes code from other apps the most common security issues for an Android application is that the data you are saving on the computer is open to other applications. There are three simple ways to store data on your device:
- Internal storage.
- External storage.
- Content provider