第36页

<h2>第1章</h2>
In Android, an application can be “alive” even if its process has been killed. Put another way, the activity life cycle is not tied to the process life cycle. Processes are just disposable containers for activities. This is probably different from every other system you’re familiar with, so let’s take a closer look before moving on.

    这一点和一般平台的程序不一样。是不是可以这么理解，Activity和主进程其实是两个“进程”，一个专门负责user interface的，一个负责计算。
You, the developer, do not have control over what state your program is in. That’s all managed by the system. However, you do get notified when the state is about to change through the onXX() method calls. You override these methods in your Activity class, and Android will call them at the appropriate time. <图片1>


Android四大关键概念：
Activity: user interface，就是脸谱了。
Intents: data transfer，运输工。
Services: worker，关键啊，劳模。
Content provider: data center，数据中心。


A resource is a localized text string, bitmap, or other small piece of noncode information that your program needs. At build time all youe resources get complied into your application.

You will create and store your resources in the res directory inside your project. The Android resource complier aapt processed resources according to which subfolder they are in and the format of the file.For example, PNG and JPG format bitmaps should go in a directorystarting with res/drawable, and XML files that describe screen layouts should go in a directory starting with res/layout.

The resource complier compress and packs your resources and then generates a class named R that contains identifiers you use to reference those resources in your program.


access to certain critical operations are restricted, and you must specifically ask for permission to use them in a file named Android-Manifest.xml.
For example, to monitor incoming SMS messages, you would specify
this in the manifest file:
<mainfest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.google.android.app.myapp">
    <use-permission android:name="android.permission.RECEIVE_SMS"/>
</manifest>