ADT comes with a built-in example program, or template, that we’re
going to use to create a simple “Hello, Android” program in just a few
seconds.
ADT帶有內(nèi)置的例子和模板,我們可以在幾秒鐘內(nèi)創(chuàng)建一個簡單的"Hello android"的例子
Get your stopwatch ready. Ready? Set? Go!
準備好秒表,ready?go
Select File > New > Project... to open the New Project dialog box. Then
select Android > Android Project, and click Next.
Enter the following information:
Project name: HelloAndroid
Build Target: Android 2.2
Application name: Hello, Android
Package name: org.example.hello
Create Activity: Hello
Min SDK Version: 8
When you’re done, it should look something like Figure 1.3, on the next
page.
Click Finish. The Android plug-in will create the project and fill it in
with some default files.
單擊 finish,android的插件就會創(chuàng)建一個工程
Eclipse will build it and package it up so it will
be ready to execute. If you get an error about missing source folders,
select Project > Clean to fix it.
OK, that takes care of writing the program; now all that’s left is to try
running it. First we’ll run it under the Android emulator.
1.3 Running on the Emulator
To run your Android program, go to the Package Explorer window,
right-click the HelloAndroid project, and select Run As > Android Appli-
cation. If you’re following along in Eclipse, you may see an error dialog
like the one in Figure 1.4, on page 25. This indicates we haven’t told
the emulator what kind of phone to emulate.
Creating an AVD
To do this, you need to create an Android Virtual Device (AVD) using
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either Eclipse or the android avd command. It’s easier to use Eclipse,
so select Yes in the AVD Error dialog to open the AVD Manager. You can
open the manager again later by selecting Window > Android SDK and
AVD Manager.
6. http://d.android.com/guide/developing/tools/avd.html
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RUNNING ON THE EMULATOR 24
Figure 1.3: New Android project
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RUNNING ON THE EMULATOR 25
Keeping Up with the Plug-In
The Android Eclipse plug-in is a work in progress that changes
much more often than the Android SDK. The version you down-
load may be different from the one I used when writing this
book, and it may contain a few, shall we say, idiosyncrasies. I
recommend you check the plug-in site monthly to pick up any
new features and fixes.
Figure 1.4: Missing Android Virtual Device (AVD)
Click the New... button, and then fill out the fields for the new AVD as
follows:
Name: em22
Target: Android 2.2 - API Level 8
SDCard: 64
Skin: Default (HVGA)
This tells Eclipse to set up a generic device called “em22,” which has the
Android 2.2 (FroYo) firmware installed. A 64MB virtual Secure Digital
(SD) card will be allocated, along with a half-VGA (320×480) display.
When you are done, you should see something like Figure 1.6, on
page 27. Because of updates in the SDK tools since this was written,
your screen may look slightly different.
Click Create AVD to create the virtual device. A few seconds later you
should see a message that the device has been created. Click OK, select
the AVD, and then click Start... and then Launch to bring it up. Close
the AVD Manager window when you’re done.
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RUNNING ON THE EMULATOR 26
Cupcake vs. Donut vs. Eclair vs. FroYo
TheversionofAndroidrunningonyouremulator(orrealphone)
mustbecompatiblewithyourprogram’sbuildtarget.Forexam-
ple, if you try to run an Android 2.2 (FroYo) program on an
Android 1.5 (Cupcake) phone, it won’t work because Android
1.5 phones can only run 1.5 or earlier programs. Android 2.2
phones, on the other hand, can run programs built for 2.2, 2.1,
2.0.1, 2.0, 1.6, 1.5, and earlier. But it may be a while before most
phones have been upgraded (if ever).
So, why not just target Android 1.5? Unfortunately, applica-
tions built for 1.5 don’t always display correctly on the larger
and smaller screens found on 1.6 phones. Luckily, there’s an
easy way to make your programs compatible with all versions
of Android. See Chapter 13, Write Once, Test Everywhere, on
page 256 for instructions.
Figure 1.5: Running the “Hello, Android” program
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RUNNING ON THE EMULATOR 27
Figure 1.6: Creating an AVD in Eclipse
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RUNNING ON A REAL PHONE 28
Shortening the Turnaround
Starting the emulator is expensive. Think about it this way—
when you first turn on your phone, it needs to boot up just like
anycomputersystem.Closingtheemulatorisjustliketurningoff
the phone or pulling the batteries out. So, don’t turn it off!
Leave the emulator window running as long as Eclipse is run-
ning. The next time you start an Android program, Eclipse will
noticetheemulatorisalreadythereandwilljustsenditthenew
program to run.
Let’s Try That Again
Once you have a valid AVD, the Android emulator window will start up
and boot the Android operating system. The first time you do this, it
may take a minute or two, so be patient. You may need to right-click
the project and select Run As > Android Application again. If you see
an error message saying that the application is not responding, select
the option to continue waiting. If you see a key guard screen, swipe it
as directed to unlock.
Eclipse will send a copy of your program to the emulator to execute.
The application screen comes up, and your “Hello, Android” program is
now running (see Figure 1.5, on page 26). That’s it! Congratulations on
your first Android program.
1.4 Running on a Real Phone
Running an Android program on a physical device such as the Droid
or Nexus One during development is almost identical to running it on
the emulator. You need to enable USB debugging on the phone itself
(by starting the Settings application and selecting Applications > Devel-
opment > USB Debugging), install the Android USB device driver if you
haven’t already (Windows only), and then plug the phone into your com-
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puter using the USB cable that came with the phone.
7. See http://d.android.com/guide/developing/device.html for the latest device driver and
installation instructions.
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FAST-FORWARD >> 29
Close the emulator window if it’s already open. As long as the phone is
plugged in, Eclipse will load and run applications on the phone instead.
When you’re ready to publish your application for others to use, there
are a few more steps you’ll need to take. Chapter 14, Publishing to the
Android Market, on page 271 will cover that in more detail.
1.5 Fast-Forward >>
Thanks to the Eclipse plug-in, creating a skeletal Android program
takes only a few seconds. In Chapter 3, Designing the User Interface, on
page 43, we’ll begin to flesh out that skeleton with a real application—a
Sudoku game. This sample will be used in several chapters to demon-
strate Android’s API.
But before delving into that, you should take a few minutes to read
Chapter 2, Key Concepts, on the following page. Once you grasp the
basic concepts such as activities and life cycles, the rest will be much
easier to understand.
Although the use of Eclipse to develop Android programs is optional, I
highly recommend it. If you’ve never used Eclipse before, you may want
to invest in a quick reference such as the Eclipse IDE Pocket Guide
[Bur05].