1、内置应用和开发的应用，没有区别
2、Linux Kernel --> Dalvik VM --> Applications
3、Kernel: 硬件抽象层，同时提供了进程、内存、文件系统管理等核心服务
Runtime: Dalvik VM，运行时环境
Code libraries: 浏览器、数据库、绘图、影音
Managers: Activities、Views、Telephony等管理器
Hardware --> Linux Kernel --> Runtime & Libraries --> Application Managers --> Applications
4、Android基于Linux Kernel，运行在Dalvik VM里
5、四种核心组件：Activity、Service、Provider、Receiver
6、A best practice is to launch Services on a periodic or as-needed basis, triggered by a system alarm, and then have the Service terminate when its task is complete
7、在manifest.xml文件里注册的Receiver组件，不需要应用启动，就可以被触发
8、每个Android Application跑在一个单独的进程里
9、在OS资源短缺的时候，Application所在的进程，有可能会被kill，不同状态的进程的优先级有区别
10、android应用不是跑在jvm里，而是跑在Dalvik VM里，所有java字节码要转换成.dex文件格式
11、strings这些资源也是被编译成binary
12、You can define layout and views directly in code or in a layout XML resource file
13、you don’t have to use an XML file at all; instead, you can define all your layout and View configuration directly in code, as Java objects. This technique is used in applications where a dynamic GUI is required. Generally speaking, it’s often easier (and better practice) to use an XML layout resource for each Activity. An XML layout file defines View objects, organized into a hierarchical tree structure. After they’re defined in relation to the parent layout,each view can then be inflated at runtime
14、Android employs a handy adapter concept used to link views that contain collections with an underlying data source
15、An Adapter is a collection handler that returns each item in the collection as a View
16、Every process running on the Android platform is placed on a stack. When you use an Activity in the foreground, the system process that hosts that Activity is placed at the top of the stack, and the previous process (the one hosting whatever Activity was previously in the foreground) is moved down one notch
17、It decides which ones to get rid of based on a simple set of priorities:
1 The process hosting the foreground Activity is the most important.
2 Any process hosting a visible but not foreground Activity is next in line.
3 Any process hosting a background Activity is next in line.
4 Any process not hosting any Activity (or Service or BroadcastReceiver) is known as an empty process and is last in line.
18、adb shell dumpsys activity
19、If the process your Activity is in falls out of the foreground, it’s eligible to be killed and it’s not up to you; it’s up to the platform’s algorithm, based on available resources and relative priorities
20、
1 onCreate()
Called when the Activity is created. Setup is done here. Also provided is access to any previously stored state in the form of a Bundle
2 onRestart()
Called if the Activity is being restarted, if it’s still in the stack, rather than starting new
3 onStart()
Called when the Activity is becoming visible on the screen to the user
4 onResume()
Called when the Activity starts interacting with the user (This method is always called, whether starting or restarting)
5 onPause()
Called when the Activity is pausing or reclaiming CPU and other resources. This method is where you should save state information so that when an Activity is restarted, it can start from the same state it was in when it quit
6 onStop()
Called to stop the Activity and transition it to a nonvisible phase and subsequent
lifecycle events
7 onDestroy()
Called when an Activity is being completely removed from system memory. This method is called either because onFinish() is directly invoked or the system decides to stop the Activity to free up resources
21、it’s important to know that onPause() is the last opportunity you have to clean up and save state information. The processes that host your Activity classes won’t be killed by the platform until after the onPause() method has completed, but they might be killed thereafter
22、The system will attempt to run through all of the lifecycle methods every time, but if resources are spiraling out of control, as determined by the platform, a fire alarm might be sounded and the processes that are hosting activities that are beyond the onPause() method might be killed at any point
23、In addition to persistent state, you should be familiar with one more scenario: instance state. Instance state refers to the state of the UI itself. The onSaveInstanceState()method is called when an Activity might be destroyed, so that at a future time the interface state can be restored
24、耗时比较多的工作，应该在UI Thread之外完成，实现的方法是使用Handler类
25、android支持自定义View组件
26、In Android, screen layout is defined in terms of ViewGroup and
LayoutParams objects. ViewGroup is a View that contains other views (has children) and also defines and provides access to the layout
