handleMessage

handleMessage is a method name used in event-driven programming to process messages delivered to a component. It is commonly associated with Android’s message-passing architecture, but the pattern appears in various libraries that use a similar design. A message is typically a small data container that carries a what field and other payload data describing the action to perform.

In Android, handleMessage is a protected method of the Handler class. A Handler runs on a thread with a Looper and a MessageQueue; Messages posted to the Handler are dispatched to its handleMessage method on that thread. Subclasses override handleMessage to implement response logic, often using msg.what to distinguish message types. A Handler can also be constructed with a Callback; if the Callback handles the message (returns true), the Handler’s own handleMessage is not invoked. A common pattern is to switch on msg.what and execute code accordingly. This mechanism enables updating UI from background threads, coordinating work, and implementing simple state machines.

Outside Android, handleMessage may refer to similarly named callbacks in other libraries or frameworks, serving as a hook for processing messages or events. The exact signature and dispatch rules vary, but the underlying idea is the same: a designated method receives a message, analyzes its content, and performs a corresponding action. See also: Handler, Looper, Message, Android.