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ANDROID DEBUG BRIDGE

The Android Debug Bridge (adb) utility permits us to interact with the Android Emu- lator directly from the command line or script. Have you ever wished you could navi- gate the filesystem on your smartphone? Well, now you can with the adb! The adb works as a client/server TCP-based application. While there are a couple of back- ground processes that run on the development machine and the emulator to enable our functionality, the important thing to understand is that when we run adb, we get access to a running instance of the Android Emulator. Here are a couple of examples of using adb. First, let’s look to see if we have any available Android Emulator sessions running:

adb devices<return>

This command will return a list of available Android Emulators; for example, figure 2.8 shows adb locating two running emulator sessions.

Let’s connect to the first Android Emu- lator session and see if our application is installed. We connect with the syntax adb shell. This is how we would connect if we

had a single Android Emulator session active, but because there are two emulators running, we need to specify an identifier to connect to the appropriate session:

adb –d 1 shell

Figure 2.9 shows off the Android filesystem and demonstrates looking for a specific installed application, namely our Chapter2 sample application, which we’ll be build- ing in the next section.

This capability can be very handy when we want to remove a specific file from the emulator’s filesystem, kill a process, or generally interact with the operating environ- ment of the Android Emulator. If you download an application from the internet, for example, you can use the adb command to install an application. For example,

adb shell install someapplication.apk

installs the application named someapplication to the Android Emulator. The file is cop- ied to the /data/app directory and is accessible from the Android application

Figure 2.9 Using the shell command, we can browse Android’s filesystem.

Figure 2.8 The adb tool provides interaction at runtime with the Android Emulator.

launcher. Similarly, if you desire to remove an application, you can run adb to remove an application from the Android Emulator. For example, if you desire to remove the Chapter2.apk sample application from a running emulator’s filesystem, you can exe- cute the following command from a terminal or Windows command window:

adb shell rm /data/app/Chapter2.apk

Mastering the command-line tools in the Android SDK is certainly not a requirement of Android application development, but having an understanding of what is available and where to look for capabilities is a good skill to have in your toolbox. If you need assistance with either the aapt or adb command, simply enter the command at the terminal, and a fairly verbose usage/help page is displayed. Additional information on the tools may be found in the Android SDK documentation.

TIP The Android filesystem is a Linux filesystem. While the adb shell com- mand does not provide a very rich shell programming environment as is found on a desktop Linux or Mac OS X system, basic commands such as

ls, ps, kill, and rm are available. If you are new to Linux, you may bene- fit from learning some very basic shell commands.

One other tool you will want to make sure you are familiar with is telnet. Telnet allows you to connect to a remote system with a character-based UI. In this case, the remote system you connect to is the Android Emulator’s console. You can accomplish this with the following command:

telnet localhost 5554

In this case, localhost represents your local development computer where the Android Emulator has been started because the Android Emulator relies on your computer’s loopback IP address of 127.0.0.1. Why port 5554? Recall when we employed adb to find running emulator instances that the output of that command included a name with a number at the end. The first Android Emulator can generally be found at IP port 5555. No matter which port number the Android Emulator is using, the Android Emulator’s console may be found at a port number equaling 1 less. For example, if the Android Emulator is running and listed at port 5555, the console is at port 5554.

Using a telnet connection to the emulator provides a command-line means for configuring the emulator while it is running and testing telephony features such as calls and text messages.

It is time to write an Android application to exercise the development environ- ment we have been discussing.

2.3

Building an Android application in Eclipse

We are going to build a simple application that gives us the opportunity to modify the UI, provides a little application logic, then executes the application in the Android Emulator. More complex applications are left for later chapters—our focus here is on

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