Develop and Debug

This page offers an introduction to developing and debugging applications on Android. It teaches how to create, build, run and debug your Android code. Alternatively, you may like to begin with the Hello Android tutorial.

Contents

1. Developing Android Applications on Eclipse
2. Developing Android Applications with Other IDEs and Tools
3. Developing on Device Hardware^new!
4. Signing Your Applications
5. Using the ApiDemos Sample Applications
6. Debugging
7. Debug and Test Settings
8. Top Debugging Tips
9. Building and Installing an Android Application
10. Removing an Android Application
11. Eclipse Tips

Developing Android Applications on Eclipse

To begin developing Android applications in the Eclipse IDE, you first create an Android project and then set up a launch configuration. After that, you can write, run, and debug your application.

The sections below provide instructions assuming that you have installed the ADT plugin in your Eclipse environment. If you haven't installed the ADT plugin, you should do that before using the instructions below. See the Installing the Eclipse Plugin (ADT) for more information.

Creating an Android Project

The ADT plugin provides a New Project Wizard that you can use to quickly create an Eclipse project for new or existing code. To create the project, follow these steps:

1. Select File > New > Project
2. Select Android > Android Project, and press Next
3. Select the contents for the project:
• Select Create new project in workspace to start a project for new code.

  Enter the project name, the base package name, the name of a single Activity class to create as a stub .java file, and a name to use for your application.

• Select Create project from existing source to start a project from existing code. Use this option if you want to build and run any of the sample applications included with the SDK. The sample applications are located in the samples/ directory in the SDK.

  Browse to the directory containing the existing source code and click OK. If the directory contains a valid Android manifest file, the ADT plugin fills in the package, activity, and application names for you.

4. Press Finish.

The ADT plugin creates these folders and files for you as appropriate for the type of project:

• src/   A folder that includes your stub .java Activity file.
• res/   A folder for your resources.
• AndroidManifest.xml   The manifest for your project.

Creating a Launch Configuration

Before you can run and debug your application in Eclipse, you must create a launch configuration for it. A launch configuration specifies the project to launch, the Activity to start, the emulator options to use, and so on.

To create a launch configuration for the application, follow these steps as appropriate for your Eclipse version:

1. Open the launch configuration manager.
   • In Eclipse 3.3 (Europa), select Run > Open Run Dialog... or Run > Open Debug Dialog... as appropriate.
   • In Eclipse 3.4 (Ganymede), select Run > Run Configurations... or Run > Debug Configurations... as appropriate.
2. In the project type list on the left, locate the Android Application item and double-click it (or right-click > New), to create a new launch configuration.
3. Enter a name for your configuration.
4. On the Android tab, browse for the project and Activity to start.
5. On the Target tab, set the desired screen and network properties, as well as any other emulator startup options.
6. You can set additional options on the Common tab as desired.
7. Press Apply to save the launch configuration, or press Run or Debug (as appropriate).

Running and Debugging an Application

Once you've set up the project and launch configuration for your application, you can run or debug it as described below.

From the Eclipse main menu, select Run > Run or Run > Debug as appropriate, to run or debug the active launch configuration.

Note that the active launch configuration is the one most recently selected in the Run configuration manager. It does not necessarily correspond to the application that is selected in the Eclipse Navigation pane (if any).

To set or change the active launch configuration, use the launch configuration manager. See Creating a Launch Configuration for information about how to access the launch configuration manager..

Running or debugging the application triggers these actions:

• Starts the emulator, if it is not already running.
• Compiles the project, if there have been changes since the last build, and installs the application on the emulator.
• Run starts the application.
• Debug starts the application in "Wait for debugger" mode, then opens the Debug perspective and attaches the Eclipse Java debugger to the application.

Developing Android Applications with Other IDEs and Tools

The recommended way to develop an Android application is to use Eclipse with the ADT plugin. This plugin provides editing, building, and debugging functionality integrated right into the IDE.

However, if you'd rather develop your application in another IDE, such as IntelliJ, or use Eclipse without the ADT plugin, you can do that instead. The SDK provides the tools you need to set up, build, and debug your application.

Creating an Android Project

The Android SDK includes activityCreator, a program that generates a number of stub files for your project, as well as a build file. You can use the program to create an Android project for new code or from existing code, such as the sample applications included in the SDK. For Linux and Mac, the SDK provides activityCreator.py, a Python script, and for Windows, activityCreator.bat, a batch script. Regardless of platform, you can use activityCreator in the same way.

To run activityCreator and create an Android project, follow these steps:

1. In the command line, change to the tools/ directory of the SDK and create a new directory for your project files. If you are creating a project from existing code, change to the root folder of your application instead.

2. Run activityCreator. In the command, you must specify a fully-qualified class name as an argument. If you are creating a project for new code, the class represents the name of a stub class that the script will create. If you are creating a project from existing code, you must specify the name of one Activity class in the package. Command options for the script include:

   • --out <folder> which sets the output directory. By default, the output directory is the current directory. If you created a new directory for your project files, use this option to point to it.
   • --ide intellij, which generates IntelliJ IDEA project files in the newly created project

Here's an example:

~/android_linux_sdk/tools $ ./activityCreator.py --out myproject your.package.name.ActivityName
package: your.package.name
out_dir: myproject
activity_name: ActivityName
~/android_linux_sdk/tools $ 

The activityCreator script generates the following files and directories (but will not overwrite existing ones):

• AndroidManifest.xml The application manifest file, synced to the specified Activity class for the project.
• build.xml An Ant file that you can use to build/package the application.
• src/your/package/name/ActivityName.java The Activity class you specified on input.
• your_activity.iml, your_activity.ipr, your_activity.iws    [only with the -ide intelliJ flag] intelliJ project files.
• res/   A directory to hold resources.
• src/    The source directory.
• bin/    The output directory for the build script.

You can now move your folder wherever you want for development, but keep in mind that you'll have to use the adb program in the tools/ folder to send files to the emulator, so you'll need access between your solution and the tools/ folder.

Also, you should refrain from moving the location of the SDK directory, since this will break the build scripts (they will need to be manually updated to reflect the new SDK location before they will work again).

Building an Android Application

Use the Ant build.xml file generated by activityCreator to build your application.

1. If you don't have it, you can obtain Ant from the Apache Ant home page. Install it and make sure it is on your executable path.
2. Before calling Ant, you need to declare the JAVA_HOME environment variable to specify the path to where the JDK is installed.

Note: When installing JDK on Windows, the default is to install in the "Program Files" directory. This location will cause ant to fail, because of the space. To fix the problem, you can specify the JAVA_HOME variable like this: set JAVA_HOME=c:\Programs\Java\. The easiest solution, however, is to install JDK in a non-space directory, for example: c:\java\jdk1.6.0_02.

3. If you have not done so already, follow the instructions for Creating a New Project above to set up the project.
4. You can now run the Ant build file by simply typing ant in the same folder as the build.xml file for your project. Each time you change a source file or resource, you should run ant again and it will package up the latest version of the application for you to deploy.

Running an Android Application

To run a compiled application, you will upload the .apk file to the /data/app/ directory in the emulator using the adb tool as described here:

1. Start the emulator (run <your_sdk_dir>/tools/emulator from the command line)
2. On the emulator, navigate to the home screen (it is best not to have that application running when you reinstall it on the emulator; press the Home key to navigate away from that application).
3. Run adb install myproject/bin/<appname>.apk to upload the executable. So, for example, to install the Lunar Lander sample, navigate in the command line to <your_sdk_dir>/sample/LunarLander and type ../../tools/adb install bin/LunarLander.apk
4. In the emulator, open the list of available applications, and scroll down to select and start your application.

Note: When you install an Activity for the first time, you might have to restart the emulator before it shows up in the application launcher, or other applications can call it. This is because the package manager usually only examines manifests completely on emulator startup.

Attaching a Debugger to Your Application

This section describes how to display debug information on the screen (such as CPU usage), as well as how to hook up your IDE to debug running applications on the emulator.

Attaching a debugger is automated using the Eclipse plugin, but you can configure other IDEs to listen on a debugging port to receive debugging information.

1. Start the Dalvik Debug Monitor Server (DDMS) tool , which acts as a port forwarding service between your IDE and the emulator.
2. Set optional debugging configurations on your emulator, such as blocking application startup for an activity until a debugger is attached. Note that many of these debugging options can be used without DDMS, such as displaying CPU usage or screen refresh rate on the emulator.
3. Configure your IDE to attach to port 8700 for debugging. We include information on how to set up Eclipse to debug your project.

Configuring your IDE to attach to the debugging port

DDMS will assign a specific debugging port to every virtual machine that it finds on the emulator. You must either attach your IDE to that port (listed on the Info tab for that VM), or you can use a default port 8700 to connect to whatever application is currently selected on the list of discovered virtual machines.

Your IDE should attach to your application running on the emulator, showing you its threads and allowing you to suspend them, inspect their state, and set breakpoints. If you selected "Wait for debugger" in the Development settings panel the application will run when Eclipse connects, so you will need to set any breakpoints you want before connecting.

Changing either the application being debugged or the "Wait for debugger" option causes the system to kill the selected application if it is currently running. You can use this to kill your application if it is in a bad state by simply going to the settings and toggling the checkbox.

Developing on Device Hardware

If you have an Android device, you can develop and debug your Android applications just as usual. Launching your apps on a device works just the same as on the emulator, but there are a few things to do before you can start.

1. Declare your application as "debuggable" in your Android Manifest.

   In Eclipse, you can do this from the Application tab when viewing the Manifest (on the right side, set Debuggable to true). Otherwise, in the AndroidManifest.xml file, add android:debuggable="true" to the <application> element.

2. Turn on "USB Debugging" on your device.

   On the T-Mobile G1, go to the home screen, press MENU, select Applications > Development, then enable USB debugging.

3. Setup your system to detect your device.
   • If you're developing on Windows (32-bit only), you need to install the USB driver for adb:
     1. Download the driver ZIP file (android_usb_windows.zip) and unzip it.
     2. Connect your Android device via USB. When the Found New Hardware Wizard appears, you'll be asked if you'd like Windows Update to search for software, select No, not this time and click Next.
     3. Select Install from a list or specified location and click Next.
     4. Select Search for the best driver in these locations. Browse and select the unzipped file.
     5. Click Finish. You're all set.
   • If you're developing on Mac OS X, it just works. Skip this step.
   • If you're developing on Ubuntu Linux, you need to add a rules file:
     1. Login as root and create this file: /etc/udev/rules.d/50-android.rules.

        For Gusty/Hardy, edit the file to read:
        SUBSYSTEM=="usb", SYSFS{idVendor}=="0bb4", MODE="0666"

        For Dapper, edit the file to read:
        SUBSYSTEM=="usb_device", SYSFS{idVendor}=="0bb4", MODE="0666"

     2. Now execute:
        chmod a+rx /etc/udev/rules.d/50-android.rules

You can verify that your device is connected by executing adb devices from your SDK tools/ directory. If connected, you'll see the device name listed as a "device."

If using Eclipse, select run or debug as usual. You will be presented with a Device Chooser dialog that lists the available emulator(s) and connected device(s). Select the device to install and run the application there.

If using the Android Debug Bridge (adb), you can issue commands with the -d flag to target your connected device.

Signing Your Applications

The information about signing your applications has moved to Signing and Publishing Your Applications.

Using the ApiDemos Sample Applications

The Android SDK includes a set of sample applications that demonstrate much of the functionality and API usage needed for your applications. The ApiDemos package is preinstalled on the emulator, so you can access it by starting an emulator and sliding open the home screen's application drawer.

You can find the source code corresponding to the ApiDemos apps in <SDK>/samples/ApiDemos. Take a look to learn more about how it is implemented.

If you want, you can load the ApiDemos sample applications as source projects and modify them, then run them in the emulator. However, to do so, you need to uninstall the preinstalled version of ApiDemos first. If you try to run or modify ApiDemos from your development environment without removing the preinstalled version first, you will get an install error.

For information about how to uninstall and then reinstall ApiDemos so that you can work with them in your development environment, see the troubleshooting topic I can't install ApiDemos apps in my IDE because of a signing error.

Debugging

Android has a fairly extensive set of tools to help you debug your programs:

• DDMS - A graphical program that supports port forwarding (so you can set up breakpoints in your code in your IDE), screen captures on the emulator, thread and stack information, and many other features. You can also run logcat to retrieve your Log messages. See the linked topic for more information.
• logcat - Dumps a log of system messages. The messages include a stack trace when the emulator throws an error, as well as Log messages. To run logcat, see the linked topic.

  ...
  I/MemoryDealer( 763): MemoryDealer (this=0x54bda0): Creating 2621440 bytes heap at 0x438db000
  I/Logger( 1858): getView() requesting item number 0
  I/Logger( 1858): getView() requesting item number 1
  I/Logger( 1858): getView() requesting item number 2
  D/ActivityManager( 763): Stopping: HistoryRecord{409dbb20 com.android.home.AllApps}
  ...

• Android Log - A logging class to print out messages to a log file on the emulator. You can read messages in real time if you run logcat on DDMS (covered next). Add a few logging method calls to your code.

  To use the Log class, you just call Log.v() (verbose), Log.d() (debug), Log.i() (information), Log.w() (warning) or Log.e (error) depending on the importance you wish to assign the log message.

  Log.i("MyActivity", "MyClass.getView() — Requesting item number " + position)

  You can use logcat to read these messages.

• Traceview - Android can save a log of method calls and times to a logging file that you can view in a graphical reader called Traceview. See the linked topic for more information.

• Eclipse plugin - The Eclipse Android plugin incorporates a number of these tools (ADB, DDMS, logcat output, and other functionality). See the linked topic for more information.
• Debug and Test Device Settings - Android exposes several settings that expose useful information such as CPU usage and frame rate. See Debug and Test Settings below.

Also, see the Troubleshooting section of the doc to figure out why your application isn't appearing on the emulator, or why it's not starting.

Debug and Test Settings

Android lets you set a number of settings that will make it easier to test and debug your applications. To get to the development settings page on the emulator, go to Dev Tools > Development Settings. This will open the development settings page with the following options (among others):

• Debug app   Selects the application that will be debugged. You do not need to set this to attach a debugger, but setting this value has two effects:
  • It will prevent Android from throwing an error if you pause on a breakpoint for a long time while debugging.
  • It will enable you to select the Wait for Debugger option to pause application startup until your debugger attaches (described next).
• Wait for debugger    Blocks the selected application from loading until a debugger attaches. This way you can set a breakpoint in onCreate(), which is important to debug the startup process of an Activity. When you change this option, any currently running instances of the selected application will be killed. In order to check this box, you must have selected a debug application as described in the previous option. You can do the same thing by adding waitForDebugger() to your code.
• Immediately destroy activities   Tells the system to destroy an activity as soon as it is stopped (as if Android had to reclaim memory).  This is very useful for testing the onSaveInstanceState(Bundle) / onCreate(android.os.Bundle) code path, which would otherwise be difficult to force. Choosing this option will probably reveal a number of problems in your application due to not saving state.
• Show screen updates    Flashes a momentary pink rectangle on any screen sections that are being redrawn. This is very useful for discovering unnecessary screen drawing.
• Show CPU usage   Displays CPU meters at the top of the screen, showing how much the CPU is being used. The top red bar shows overall CPU usage, and the green bar underneath it shows the CPU time spent in compositing the screen. Note: You cannot turn this feature off once it is on, without restarting the emulator.
• Show background   Displays a background pattern when no activity screens are visible. This typically does not happen, but can happen during debugging.

These settings will be remembered across emulator restarts.

Top Debugging Tips

Quick stack dump

To obtain a stack dump from emulator, you can log in with adb shell, use "ps" to find the process you want, and then "kill -3 ". The stack trace appears in the log file.

Displaying useful info on the emulator screen

The device can display useful information such as CPU usage or highlights around redrawn areas. Turn these features on and off in the developer settings window as described in Debug and Test Settings.

Getting system state information from the emulator (dumpstate)

You can access dumpstate information from the Dalvik Debug Monitor Service tool. See dumpsys and dumpstate on the adb topic page.

Getting application state information from the emulator (dumpsys)

You can access dumpsys information from the Dalvik Debug Monitor Service tool. See dumpsys and dumpstate on the adb topic page.

Getting wireless connectivity information

You can get information about wireless connectivity using the Dalvik Debug Monitor Service tool. From the Device menu, select "Dump radio state".

Logging Trace Data

You can log method calls and other tracing data in an activity by calling android.os.Debug.startMethodTracing(). See Running the Traceview Debugging Program for details.

Logging Radio Data

By default, radio information is not logged to the system (it is a lot of data). However, you can enable radio logging using the following commands:

adb shell
logcat -b radio

Running adb

Android ships with a tool called adb that provides various capabilities, including moving and syncing files to the emulator, forwarding ports, and running a UNIX shell on the emulator. See Using adb for details.

Getting screen captures from the emulator

Dalvik Debug Monitor Server (DDMS) can capture screenshots from the emulator.

Using debugging helper classes

Android provides debug helper classes such as util.Log and Debug for your convenience.

Building and Installing an Android Application

Android requires custom build tools to be able to properly build the resource files and other parts of an Android application. Because of this, you must have a specialized build environment for your application.

Custom Android compilation steps include compiling the XML and other resource files, and creating the proper output format. A compiled Android application is an .apk file, which is a compressed file containing .dex files, resource files, raw data files, and other files. You can create a properly structured Android project either from scratch, or from existing source files.

Android does not currently support development of third party applications in native code (C/C++).

The recommended way to develop an Android application is to use Eclipse with the Android plugin, which provides support for building, running, and debugging Android applications.

If you have another IDE, Android provides tools for other IDEs to build and debug Android applications, but they are not as integrated.

Removing an Android Application

To remove an application that you have installed on the emulator, you will need to run adb and delete the .apk file you sent to the emulator when you installed it. Use adb shell to drop into a shell on the device as described in the linked topic, navigate to data/app/, and then remove the file using rm your_app.apk.

Eclipse Tips

Executing arbitrary Java expressions in Eclipse

You can execute arbitrary code when paused at a breakpoint in Eclipse. For example, when in a function with a String argument called "zip", you can get information about packages and call class methods. You can also invoke arbitrary static methods: for example, entering android.os.Debug.startMethodTracing() will start dmTrace.

Open a code execution window, select Window>Show View>Display from the main menu to open the Display window, a simple text editor. Type your expression, highlight the text, and click the 'J' icon (or CTRL + SHIFT + D) to run your code. The code runs in the context of the selected thread, which must be stopped at a breakpoint or single-step point. (If you suspend the thread manually, you have to single-step once; this doesn't work if the thread is in Object.wait().)

If you are currently paused on a breakpoint, you can simply highlight and execute a piece of source code by pressing CTRL + SHIFT + D.

You can highlight a block of text within the same scope by pressing ALT +SHIFT + UP ARROW to select larger and larger enclosing blocks, or DOWN ARROW to select smaller blocks.

Here are a few sample inputs and responses in Eclipse using the Display window.

Input	Response
zip	(java.lang.String) /work/device/out/linux-x86-debug/android/app/android_sdk.zip
zip.endsWith(".zip")	(boolean) true
zip.endsWith(".jar")	(boolean) false

You can also execute arbitrary code when not debugging by using a scrapbook page. Search the Eclipse documentation for "scrapbook".

Running DDMS Manually

Although the recommended way to debug is to use the ADT plugin, you can manually run DDMS and configure Eclipse to debug on port 8700. (Note: Be sure that you have first started DDMS).

Adding JUnit test classes

In Eclipse/ADT, you can add JUnit test classes to your application. However, you need to set up a custom JUnit configuration before your tests will run properly. For detailed information about how to set up the JUnit configuration, see the troubleshooting topic I can't run a Junit test class in Eclipse.