Android ListView and Adapters

Adapter Overview

• An adapter acts as a bridge between a data source and a UI.
• It reads data from various sources, converts it into UI elements, and provides it to the UI component.
• Data sources include arrays, lists, and databases.

Adapter in Android

• Data source can be an Array, List, or similar object.
• BaseAdapter is the parent class for custom adapters.
• Android SDK provides ready-to-use adapters like ArrayAdapter and SimpleAdapter.
• Custom adapters extend BaseAdapter and override methods for customization.

Adapter View in Android

• Used for efficiently displaying large datasets in the UI.
• Leverages memory and CPU optimization techniques to prevent lag.
• Only renders items currently visible or about to be; reuses layouts when scrolling.

Adapters in Android

• BaseAdapter—Parent adapter for others.
• ArrayAdapter—Used for lists of single items backed by arrays.
• Custom ArrayAdapter—Used for custom list displays.
• SimpleAdapter—Maps static data to views defined in XML.
• Custom SimpleAdapter—Used for customized lists and accessing child elements.

Spinner with Array Adapter

• Demonstrates creating a spinner using ArrayAdapter.
• Extends AppCompatActivity for spinner functionality.
• Sets data, dropdown layout, and adapter for the spinner.
• Provides toast display on item selection.

Android ListView

• A scrollable list view component in Android.
• Uses an adapter to populate data from sources (e.g., arrays, databases).
• Automatically inserts items into the list.

ListView Usage

• Used for vertically scrolling lists of items (like contact lists).
• Allows users to easily browse information, with options to set dividers and item heights.
• Can display TextView, ImageView, or a mix of UI elements to represent list items.
• Leverages adapter classes to handle data efficiently for large datasets.

GridView in Android

• Two-dimensional, scrollable grid component in Android.
• Grid items insert automatically using a list adapter.
• Adapters pull data from sources (e.g., arrays, databases), convert items to displayable views, and place them in the grid.

SearchView

• An Android component providing a search interface.
• Users enter a query; the component submits to a provider and displays suggestions or results.
• Supports selecting suggestions or results.

SearchView Methods

• getQuery(): Returns the current query string.
• getQueryHint(): Returns the hint text for the search field.
• isIconfiedByDefault(): Returns the default iconified state of the search field.
• setQueryHint(): Sets the hint text for the query field.
• setOnQueryTextFocusChangeListener(): Handles focus change events in the search field.
• setOnQueryTextListener(): Listens for submit and change events in the search query.

Attributes of SearchView

• queryHint: Sets the hint text for the empty query field.
• iconifiedByDefault: Controls the initial iconified state (collapsed or expanded).
• background: Sets the background of the search view.

Custom Array Adapter

• Customizes the ArrayAdapter component.
• Overrides BaseAdapter methods to provide extended functionality for a list view or recycler view.
• Offers more complex layouts.

getCount()

• Returns the total number of items in the adapter.
• Typically used in adapters to fetch and return the size of the underlying data source.

getView()

• Called when a list item is displayed or about to be displayed.
• Used to populate list or grid elements with data.
• Retrieves data for each item & binds the data to corresponding UI views (e.g., TextView, ImageView) for the item.

SimpleAdapter

• An easy adapter to map static data to views in an XML layout file.
• Accepts data as an ArrayList of Maps, where each map represents a row's data.
• Works with XML layouts defined for your list item views.

Context parameter of SimpleAdapter

• Used to retrieve the current application context; needed for creating UI elements.

data parameter of SimpleAdapter

• Contains the data to populate the ListView/GridView, in the form of a List of Map objects.

resource parameter of SimpleAdapter

• Integer representing the resource Id of your custom layout for each row.

from parameter of SimpleAdapter

• Array String objects representing the keys for data in the rows from the Map objects.

to parameter of SimpleAdapter

• Array of integers representing the views in the layout associated with each String key (from).

Android GridView

• Used to display data in a two-dimensional grid or scrollable grid on Android devices.

Recycler View

• An advanced, efficient view for displaying lists and grids of items on Android.
• Enables display of large datasets without performance issues.
• Uses ViewHolders to improve performance when recycling and updating items.
• Requires specifying LayoutManager and Adapter to work.

Layout Managers

• LinearLayoutManager: Displays items vertically or horizontally, useful when displaying data as a list.
• GridLayoutManager: Displays items in a grid format.
• StaggeredGridLayoutManager: Displays items in a staggered grid format.

ViewHolder

• An inner class within the RecyclerView Adapter for reusing and managing views.
• Reduces findViewById calls when recycling views, improving performance.