In Android, what is AIDL (Android Interface Definition Language) and which kinds of data types are supported by AIDL interfaces for interprocess communication?

Introduction / Context:
Android Interface Definition Language, usually shortened to AIDL, is a mechanism for defining clear interfaces between processes on Android. This question evaluates whether you understand both the purpose of AIDL and the kinds of data types that can be marshaled across process boundaries. These concepts are important when building bound Services that are accessed from multiple applications.

Given Data / Assumptions:

• Communication is happening between different processes in Android, such as a client Activity and a remote Service.
• AIDL is used when the client and Service need to perform remote method calls.
• Data types passed through AIDL must be marshaled and unmarshaled safely by the system.

Concept / Approach:
AIDL lets you define an interface in a special .aidl file. From this definition, the Android build tools generate code that handles low level details of interprocess communication. Not all Java data types can be transferred through AIDL. Supported types include Java primitive types such as int, long, boolean, and double, as well as String and CharSequence. AIDL also supports Parcelable objects, List collections, Map collections, and other AIDL generated interfaces, but all must follow clear rules so that the system can flatten and rebuild them across processes.

Step-by-Step Solution:
Step 1: Identify that AIDL is specifically designed for remote procedure calls between processes.Step 2: Recall the list of allowed data types, which includes all Java primitive types, String, CharSequence, and custom Parcelable classes.Step 3: Understand that collections such as List and Map are supported, but their contents must themselves be of supported types.Step 4: Recognize that layout definition, logging, or encryption are not primary concerns of AIDL.Step 5: Comparing the options, only option A correctly describes both the purpose of AIDL and the supported data categories.

Verification / Alternative check:
Reviewing official documentation confirms that AIDL is used to define interface methods that a client can call on a Service running in another process. Documentation also enumerates supported data types, including primitive types, String, CharSequence, Parcelable, List, and Map, with restrictions. No evidence suggests that AIDL is a layout language, logging framework, or encryption layer, which validates the correctness of option A.

Why Other Options Are Wrong:
Option B is wrong because XML layouts are defined in .xml files under the res directory, not in AIDL files, and the description of supported data types is incomplete. Option C misidentifies AIDL as a logging framework and ignores its real use in remote procedure calls. Option D incorrectly labels AIDL as an encryption feature, which it is not; AIDL focuses on interface definition and marshalling, not cryptography.

Common Pitfalls:
Developers sometimes try to pass unsupported complex objects or generics through AIDL, resulting in build errors or runtime failures. Another common pitfall is forgetting that AIDL calls occur on Binder threads, so long running work must be offloaded to avoid blocking the system. It is also important to keep AIDL interfaces stable, because changes affect both client and Service implementations and require regeneration of the stub code.

Final Answer:
AIDL is Android Interface Definition Language used to define programming interfaces for interprocess communication and it supports primitive types, String, CharSequence, List, Map, and Parcelable types.