[Android studio] Section 17 Adapter Adapter

Table of contents

1. What is Adapter?

2. Detailed explanation of Adapter

1. What is Adapter?

In Android development, the adapter (Adapter) is a key component, used to bind data sources to view components on the interface, such as ListView, RecyclerView, Spinner, etc. The main role of the adapter is to create each list item or view item based on the content of the data source and display it in the corresponding container.

2. Detailed explanation of Adapter

When instantiating the adapter's constructor, you usually need to pass in the following parameters:

1. Context object: Context object, used to obtain system resources and perform operations. Generally, you can pass in the context of the current Activity or Application.

2. Data source: The data source to be displayed by the adapter, which can be an array, collection, database query results, etc.

3. Other optional parameters: Different adapter classes may also need to pass in other parameters to configure the behavior of the adapter. These parameters depend on the specific adapter class.

It should be noted that different adapter classes may have different constructors that accept different parameter types and numbers. You can choose the appropriate adapter class based on specific usage scenarios and needs, and understand the parameters required by the class and their meanings. When creating an adapter object, pass in the corresponding parameters according to the constructor of the adapter class to ensure that the adapter can work correctly and interact with the data source and view.

The Adapter class usually contains the following important methods in Android development:

1. getCount(): Returns the number of items in the data source.

2. getItem(): Get the list item or view item data at the specified position based on the position.

3. getItemId(): Get the item ID of the specified location based on the location.

4. getView(): Gets the view object required for each list item or view item and populates the data into the view. This is one of the most important methods in the adapter.

Additionally, adapters may involve other methods to handle specific needs, depending on the adapter class used. Here are some common adapter methods:

1. onCreateViewHolder() and onBindViewHolder() (RecyclerView.Adapter): used to create view items and bind data to view items, used to support RecyclerView.

2. getViewTypeCount() and getItemViewType() (BaseAdapter): used to define different types of view items and return the number and index of different types.

3. swapCursor() and changeCursor() (CursorAdapter): Used to switch or change the Cursor object to update the adapter's data source.

4. add(), remove(), clear(), etc. (ArrayAdapter, BaseAdapter): used to add, remove and clear items in the data source.

These methods provide interaction between the adapter and data sources, view items, and operations. By implementing the adapter's approach, you can tailor the adapter's behavior as needed to meet specific business needs and ensure that data is displayed correctly in the appropriate view.