你我皆凡人Android
忧伤的句子
完整反义词Android, as a system, is a Java—bad operating system that runs on the Linux 2。6 kernel. The system is very lightweight and full featured。 Android applications are developed using Java and can be ported rather easily to the new platform。 If you have not yet downloaded Java or are unsure about which version you need， I detail the installation of the development environment in Chapter 2。 Other features of Android include an accelerated 3—D graphics engine (bad on hardware support)， databa support powered by SQLite, and an integrated web browr。
If you are familiar with Java programming or are an OOP developer of any sort, you are likely ud to programmatic ur interface （UI） development—that is， UI placement which is handled directly within the program code. Android, while recognizing and allowing for programmatic UI development， also supports the newer, XML-bad UI layout. XML UI layout is a fairly new concept to the average desktop developer。 I will cover both the XML UI layout and the programmatic UI development in the supporting chapters of this book。
One of the more exciting and compelling features of Android is that， becau of its architecture， third—party applications—including tho that are “home grown”—are executed with the same system priority as tho that are bundled with the core system。 This is a major departure from most systems, which give embedded system apps a greater execution priority than the thread priority available to apps created by third—party developers. Also， each application is executed within its own thread using a very lightweight virtual machine。
Aside from the very generous SDK and the well-formed libraries that are available to us to develop with, the most exciting feature for Android developers is that we now have access to anything the operating system has access to. In other words, if you want to create an application that dials the phone, you have access to the phone’s dialer; if you want to create an application that utilizes the phone’s internal GPS (if equipped)， you have access to it. The potential for developers to create dynamic and intriguing applications is now wide open。
On top of all the features that are available from the Android side of the equation， Google has thrown in some very tantalizing features of its own。 Developers of Android applications will be able to tie their applications into existing Google offerings such as Google Maps and the omniprent Google Search. Suppo you want to write an application that pulls up a Google map of where an incoming call is emanating from， or you want to be able to store common arch results with your contacts; the doors of possibility have been flung wide open with Android.h310主板
疣的种类Chapter 2 begins your journey to Android development. You will learn the how’s and why’s of using specific development environments or integrated development environments (IDE）， and you will download and install the Java IDE Eclip.
Application Components
静脉炎分级标准
A central feature of Android is that one application can make u of elements of other applications （provided tho applications permit it）。 For example, if your application needs to display a scrolling list of images and another application has developed a suitabl
e scroller and made it available to others, you can call upon that scroller to do the work， rather than develop your own. Your application doesn't incorporate the code of the other application or link to it。 Rather, it simply starts up that piece of the other application when the need aris.
For this to work, the system must be able to start an application process when any part of it is needed， and instantiate the Java objects for that part. Therefore, unlike applications on most other systems， Android applications don't have a single entry point for everything in the application （no main() function， for example)。 Rather, they have esntial components that the system can instantiate and run as needed。 There are four types of components:which从句
Activities
An activity prents a visual ur interface for one focud endeavor the ur can undertake。 For example， an activity might prent a list of menu items urs can choo from or it might display photographs along with their captions. A text messaging a
pplication might have one activity that shows a list of contacts to nd messages to， a cond activity to write the message to the chon contact， and other activities to review old messages or change ttings. Though they work together to form a cohesive ur interface， each activity is independent of the others。 Each one is implemented as a subclass of the Activity ba class.
懒熊An application might consist of just one activity or, like the text messaging application just mentioned, it may contain veral。 What the activities are， and how many there are depends, of cour, on the application and its design。 Typically， one of the activities is marked as the first one that should be prented to the ur when the application is launched. Moving from one activity to another is accomplished by having the current activity start the next one.
