原创 1st Reading note of Android A Programmer's Guide

Today i read the book<Android - A Programmer's Guide> written by J.F. DiMarzio .

1. downloading and installing Java Runtime Environment (JRE)
The JRE allows you to run Java-based applications, but it does not allow you
to create them. To create Java applications, you need to download and install the Java
Development Kit (JDK), which contains all the tools and libraries needed to create Java
applications. If you are not familiar with Java, keep these differences in mind.

Sun Developer Network (SDN) Downloads page at http://
developers.sun.com/downloads/,

2. downloading and installing Eclipse
the Eclipse Downloads page at www.eclipse.org/downloads
Download the Eclipse IDE for Java Developers from this site. The package is relatively
small (79MB) and should download fairly quickly. Be sure not to download the Eclipse
IDE for Java EE Developers, as this is a slightly different product and I will not be
covering its usage.

3. download and install the Android SDK
download the Android SDK from the Google Android
development site, located at http://code.google.com/android

4. download and install the Android plugin for Eclipse
    1. Open the Eclipse application. You will download the Android plugin for Eclipse from
within the Eclipse IDE.
    2. Choose Help | Software Updates | Find and Install.
    3. In the Install/Update window, which allows you to begin the process of downloading
and installing any of the plugins that are available to you for Eclipse, click the Search
for New Features to Install radio button and then click Next.
    4. The Update Sites to Visit page of the Install window, shown next, lists all the default
websites used for obtaining Eclipse plugins. However, the plugin you want, Android
for Eclipse, is not available from the default sites. To download the Android plugin,
you must tell Eclipse where to look for it, so click the New Remote Site button.
    5. In the New Update Site dialog box, shown next, you must enter two pieces of
information to continue: a name for your new site, and its associated URL. The
name is only for display purposes and does not affect the downloading of the plugin.
In the Name field, enter Android Plugin. In the URL field, enter the URL from
which Eclipse will obtain information about the plugins that are available:
https://dl-ssl.google.com/android/eclipse/. Click OK.
    6. A new site named Android Plugin should now be in your list of available sites:
At this point Eclipse has not yet looked for the plugin; this is just a list of paths that you
can tell Eclipse to check when looking for new plugins to install.
    7. Check the check box next to Android Plugin and then click Finish. Eclipse searches the
URL associated with the Android Plugin site for any available plugins.
    8. On the Search Results page of the Updates window, select the Android Plugin and then
click Finish.
    9. On the Feature License page of the Install window, shown next, accept the licensing
agreement for the Android Development Tools and click Next.

Keep in mind that all Eclipse plugins are installed to the %installpath%/eclipse/plugins
directory. This information will help you if you need to locate the files that make up the
Android plugin.

    10. Eclipse downloads the Android plugin. At the time of this writing, the plugin version is
0.4.0.200802081635. On the final plugin installation page, Feature Verification, click
Install All to complete the installation of the Android plugin.
With the Android plugin installed, the last step you have to perform is to configure
the plugin.

5. configuring the Android plugin for Eclipse
The Android plugin for Eclipse is configured from the Preferences window of Eclipse.
Proceed as follows:
    1. From the main Eclipse window, choose Window | Preferences.
    2. In the Preferences window, shown next, select Android in the menu on the left. On the
right side of the window, click Browse, find the location of the Android SDK on your
hard drive, and enter it in the SDK Location field. Eclipse needs this information to be
able to access all the tools that are supplied with Android, such as the emulator.
    3. Check the Automatically Sync Projects to Current SDK check box and then
click Apply.
    4. The final step in setting up the Android SDK is to put it into your PATH statement. If
you are using a Microsoft Windows machine, right-click Computer (or My Computer,
depending on your version of Windows) and select Properties to open the System
Properties dialog box. Click the Advanced tab.
    5. Click Environment Variables to display the window of the same name, shown in the
following illustration. This is where you can edit your PATH statement.
    6. Under System Variables, find the variable PATH and double-click it.
    7. In the Edit System Variable dialog box, shown next, add the location of your Android
SDK?aseparated from the existing paths by a semicolon?aand click OK to apply your
changes, and click OK again in the Environment Variables window.

I suggest that anyone faced with the possibility of upgrading from one version of an SDK/plugin
combo to another use this same process: simply uninstall the older version, and install
the newer one, rather than upgrading.

6. What is the Android SDK?
The bulk of the Android SDK, in number of files, consists of documentation, with
programming APIs, tools, and samples comprising the rest.

While there are a few files in the root folder, like
android.jar (a compiled Java application containing the core SDK libraries and APIs) and
some release notes, the remainder of the Android SDK is divided into three main folders:
    Docs Contains all of the accompanying Android documentation
    Samples Contains six sample applications that you can compile and test from
within Eclipse
    Tools Contains all of the development, compilation, and debugging tools that you
need throughout the development process of an Android application

6.1 The Android documentation
    The Android documentation is located in the Docs folder within the Android SDK at
../%sdk folder%/DOCS.
    The documentation is in HTML format and can be
accessed though the documentation.html file in the root of the SDK folder.
    For me, the most valuable segments of
the Android SDK documentation are as follows (as they appear in the navigation bar):
    Reference Information
    ?? Class Index
    ?? List of Permissions
    ?? List of Resource Types
    FAQs
    ?? Troubleshooting
   
Using Eclipse, load the API Demos application as a New Android Project. To do this,
select File | New | Project from the Eclipse menu bar; a New Android Project wizard
opens. Do not worry about the options in this wizard for now. Simply select Create
Project From Existing Source and browse to the folder with the API Demo application
in it. When the project is loaded, choose Run to see it execute in the Android Emulator.

6.2 The Android Tools
    emulator.exe emulator.exe is going to be your only means to test applications on a ?°native?± platform.
    adb.exe Android Debug Bridge or adb This tool allows you to issue commands to the Emulator.exe tool.
        the adb tool allows you to do the following:
        ?? Start and stop the server
        ?? Install and uninstall applications
        ?? Move files to and from the emulator
    MKSDCARD.exe is a very useful tool if you are testing an application that will need
            to read or write files to or from an SD Memory Card inserted into the mobile device.
    DX.exe is the compiler of the Android SDK. When run against your Java files, DX.exe
        will create files with .dex extensions?aDalvik executable format.
    activityCreator(.bat or .pn) is a simple command-line tool that is used to set up a basic development
        environment.If you are in a Windows environment, this will be a .bat file; otherwise it will be a python (.pn) script.
   
   
    Extensible Messaging and Presence Protocol (XMPP)developed
by the Jabber open source community. Using XMPP, applications can quickly become
aware of other clients?ˉ presence and availability for the purpose of messaging and
communications.

6.3 standard ASP application life cycle
These steps are required to be implemented
by all ASP applications, and really define what an ASP application is. The steps, in
order, are
    1. Application_Start
    2. Event
    3. HTTPApplication.Init
    4. Disposal
    5. Application_End
6.4 The Android application life cycle
The Android application life cycle is unique in that the system controls much of the life
cycle of the application. All Android applications, or Activities, are run within their own
process.
Some of the specific methods called during the life cycle of an android activity are
?? onCreate
?? onStart
?? Process-specific events (for example: launching activities or accessing a database)
?? onStop
?? onDestroy

7. The application and Activity
You will often see ?°application?± and ?°Activity?± used interchangeably. The difference
between the two is that an application can be composed of multiple Activities, but
one application must have at least one Activity. Each ?°window?± or screen of your
application is a separate Activity. Therefore, if you create a fairly simple application
with only one screen of data (like the Hello World! application in this chapter), that will
be one Activity. In future chapters you will create applications with multiple Activities.

CAUTION
Do not select Java Project from the New menu. While Android applications are written
in Java, and you are doing all of your development in Java projects, this option will
create a standard Java application. Selecting Android Project enables you to create
Android-specific applications.
If you do not see the option for Android Project, this indicates that the Android plugin
for Eclipse was not fully or correctly installed. Review the procedure in Chapter 3 for
installing the Android plugin for Eclipse to correct this.

The New Android Project wizard creates two things for you:
?? A shell application that ties into the Android SDK, using the android.jar file, and
ties the project into the Android Emulator. This allows you to code using all of
the Android libraries and packages, and also lets you debug your applications in
the proper environment.
?? Your first shell files for the new project. These shell files contain some of the
vital application blocks upon which you will be building your programs. In
much the same way as creating a Microsoft .NET application in Visual Studio
generates some Windows-created program code in your files, using the Android
Project wizard in Eclipse generates your initial program files and some
Android-created code.

If the Package Explorer is not open, you can activate it by choosing Window | Show
View | Package Explorer.

7.1 AndroidManifest.xml file
The AndroidManifest.xml file is where your global settings are made.
The standard AndroidManifest.xml file should contain the following information:
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android=http://schemas.android.com/apk/res/android
package="testPackage.HelloWorldText">
<application android:icon="@drawable/icon">
<activity class=".HelloWorldText" android:label="@string/app_name">
<intent-filter>
<action android:value="android.intent.action.MAIN" />
<category android:value="android.intent.category.LAUNCHER"/>
</intent-filter>
</activity>
</application>
</manifest>

7.2 Referenced Libraries
A list of the Referenced Libraries is also included in the root of the project.
Given that this is a new Android project, you will see one library
in your project?ˉs references, android.jar, the Android SDK.
The application needs to reference the SDK to gain
access to all the classes contained in the SDK libraries, such as your Views, Controls,
and even the Google API.

7.3 directories
There are also three directories in the project root?ares, assets, and src?aeach of which
has a distinct purpose.

7.3.1 res directory
The res directory is where your in project resources are held and compiled into your
application. When you create a new Android project, the res directory contains three
subdirectories: drawable, layout, and values. You will use the drawable and layout
directories in many of your projects to hold and display images and layouts respectively,
whereas the values directory holds string globals that can be used throughout your
application.
NOTE
A reference to the res directory and its contents is contained by the R.java file, located
in the src directory.

7.3.1.1 drawable directory
The drawable directory contains actual image files that your application can use and
reference.

7.3.1.2 layout directory
The layout directory holds an XML file, main.xml, that is referenced by your
application when building its interface.
An unaltered main.xml file
contains the following code:
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android=http://schemas.android.com/apk/res/android
android:orientation="vertical"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
>
<TextView
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:text="Hello World, HelloWorldText"
/>
</LinearLayout>

7.3.1.3 values directory
The last directory under res, values, holds an XML file named strings. The strings.xml
file is used to hold global string values that can be referenced by your application.

7.3.2 assets directory
The assets directory is used to hold raw asset files. The files contained in the assets
directory can include audio files for streaming and animation assets.

7.3.3 src directory
The src directory contains all the source files for your project. When your project
is first created, it will contain two files, R.java and <activity>.java (in this example,
HelloWorldText.java), described next.

NOTE
<activity>.java is always named according to your Activity name.

7.3.3.1 R.java
The file R.java is an auto-generated file that is added to your application
by the Android plugin. This file contains pointers into the drawable, layout, and values
directories (or the items within the directories, as is the case with strings and icons).
You should never have to modify this file directly. You will be referencing R.java in
most of your applications.

7.4 program the UI in code rather than by using the xml file
you will program the UI in code rather than by using the xml file?aand you will
actually do most of the work. The first step here is to remove the TextView code that is in
main.xml. The following section of code represents the TextView. Removing it essentially
makes your application an empty shell.
<TextView
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:text="Hello World, HelloWorldText"
/>
After you have removed the TextView code, your main.xml file should look like this:
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android=http://schemas.android.com/apk/res/android
android:orientation="vertical"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
>
</LinearLayout>
Now that you have a clean main.xml file, and thus a clean application shell, you can
begin to add the code that will display ?°Hello World!?± on the screen. Start by opening the
HelloWorldText.java file and removing the following line:
setContentView(R.layout.main);
This line uses setContentView( ) to draw the main.xml file to the screen. Since you
will not be using main.xml to define your TextView, you will not be setting it to your
view. Instead, you will be building the TextView in code.
Your next step is to import the package TextView from android.widget. This will
give you access to the TextView and let you create your own instance of it. Place this
code near the top of your current HelloWorldText.java file, where the existing import
statements are
import android.widget.TextView;
Now, create an instance of TextView. By creating the TextView instance, you can use
it to display text to the screen without directly modifying main.xml. Place the following
code after the onCreate( ) statement is fired:
TextView HelloWorldTextView = new TextView(this);

The preceding line creates an instance of TextView named HelloWorldTextView
and then instantiates HelloWorldTextView, by setting it to a new TextView. The new
TextView is passed the context of this to be fully instantiated.
Now that the TextView is defined, you can add your text to it. The following line of
code assigns the text ?°Hello World!?± to the TextView:
HelloWorldTextView.setText("Hello World!");
You have to use the following code to set TextView
to the context and display it to the screen:
setContentView(HelloWorldTextView);