Question

android activity，intent，service是什么关系?

Answer 1

intent是activity和service的桥梁，通信员，activity主要操作显示界面，service在后台运行，适合长时间运行，如下载，听歌等。。

Answer 2

public class
Activity
extends ContextThemeWrapper
implements ComponentCallbacks KeyEvent.Callback LayoutInflater.Factory2 View.OnCreateContextMenuListener Window.Callback
An activity is a single, focused thing that the user can do. Almost all activities interact with the user, so the Activity class takes care of creating a window for you in which you can place your UI with setContentView(View). While activities are often presented to the user as full-screen windows, they can also be used in other ways: as floating windows (via a theme with windowIsFloating set) or embedded inside of another activity (using ActivityGroup).
翻译完上面这段你就知道了什么是activity了
public class
Intent
extends Object
implements Parcelable Cloneable
An intent is an abstract description of an operation to be performed.

public abstract class
Service
extends ContextWrapper
implements ComponentCallbacks
A Service is an application component representing either an application's desire to perform a longer-running operation while not interacting with the user or to supply functionality for other applications to use.