This document offers some helpful guidance to debugging applications on Android.
The Android SDK includes a set of tools to help you debug and profile
your applications. Here are some tools that you'll use most often:
- Android Debug Bridge
- Provides various device management capabilities, including
moving and syncing files to the emulator, forwarding ports, and running a UNIX
shell on the emulator.
- Dalvik Debug Monitor Server
- 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.
- A graphical viewer that displays trace file data for method calls and times saved by
your application, which can help you profile the performance of your application.
- Dumps a log of system
messages. The messages include a stack trace when the device throws an error,
as well as
Log messages you've written from your application. To run
adb logcat from your Android SDK
directory or, from DDMS, select Device > Run
logcat. When using the ADT plugin for
Eclipse, you can also view logcat messages by opening the Logcat view, available from
Window > Show View > Other > Android > Logcat.
Log is a logging
class you can use to print out messages to the logcat. You can read messages
in real time if you run logcat on DDMS (covered next). Common logging methods include:
v(String, String) (verbose),
d(String, String) (debug),
w(String, String) (warning) and
e(String, String) (error). For example:
Log.i("MyActivity", "MyClass.getView() — get item number " + position);
The logcat will then output something like:
I/MyActivity( 1557): MyClass.getView() — get item number 1
Logcat is also the place to look when debugging a web page in the Android Browser app. See
Debugging Web Pages below.
For more information about all the development tools provided with the Android SDK, see the Tools document.
In addition to the above tools, you may also find the following useful for debugging:
- Eclipse ADT
- The ADT Plugin for Eclipse integrates a number of the Android development tools (ADB, DDMS,
logcat output, and other functionality), so that you won't work with them directly but will utilize
them through the Eclipse IDE.
- Developer Settings in the Dev Tools app
- The Dev Tools application included in the emulator system image exposes several settings
that provide useful information such as CPU usage and frame rate. See Debugging and Testing with Dev Tools below.
Debugging and Testing with Dev Tools
With the Dev Tools application, you can enable a number of settings on your device that will
make it easier to test and debug your applications.
The Dev Tools application is installed by default
on all system images included with the SDK, so you can use it with the Android Emulator. If you'd
like to install the Dev Tools application on a real development device, you can copy the
application from your emulator and then install it on your device using ADB. To copy the
application from a running emulator, execute:
adb -e pull /system/app/Development.apk ./Development.apk
This copies the .apk file into the current directory. Then install it on your connected device
adb -d install Development.apk
To get started, launch the Dev Tools application and
select Development Settings. This will open the Development Settings page with the
following options (among others):
- Debug app
- Lets you select the application to debug. 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
- 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.
- 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.
- 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
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 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.
Debugging Web Pages
See the Debugging Web Apps document.
Top Debugging Tips
- Dump the stack trace
- To obtain a stack dump from emulator, you can log
adb shell, use "ps" to find the process you
want, and then "kill -3 ". The stack trace appears in the log file.
- Display 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 Setting debug and test
configurations on the emulator.
- Get 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.
- Get 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.
- Get wireless connectivity information
- You can get information about wireless connectivity using the Dalvik Debug
Monitor Service tool. From the Device menu, select "Dump
- Log trace data
- You can log method calls and other tracing data in an activity by calling
startMethodTracing(). See Running the Traceview Debugging
Program for details.
- Log 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:
logcat -b radio
- Capture screenshots
- The Dalvik Debug Monitor Server (DDMS) can capture screenshots from the emulator. Select
Device > Screen capture.
- Use debugging helper classes
- Android provides debug helper classes such as
Debug for your convenience.
Also see the Troubleshooting document
for answers to some common developing and debugging issues.
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
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.