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This document offers some helpful guidance to debugging applications on Android.
The Android SDK includes 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 ADT Plugin
for Eclipse integrates 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 on the Emulator 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
With the Dev Tools application, you can turn on 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, launch the
Dev Tools application and open 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
Setting debug and test
configurations on the emulator.
- 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.
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