Android 应用框架

Android的每一个应用运行在一个安全的沙箱中：

1.系统给每个应用一个UserID，设置该ID对该应用的所有文件有操作权限。

2.每个应用都会创建一个独立的VM。

There are separate methods for activiting each type of component:

• You can start an activity (or give it something new to do) by passing an Intent to startActivity() or startActivityForResult() (when you want the activity to return a result).
• You can start a service (or give new instructions to an ongoing service) by passing an Intent to startService(). Or you can bind to the service by passing an Intent to bindService().
• You can initiate a broadcast by passing an Intent to methods like sendBroadcast(), sendOrderedBroadcast(), or sendStickyBroadcast().
• You can perform a query to a content provider by calling query() on a ContentResolver.