Debugging Tasks

This document offers some helpful guidance to debugging applications on Android.

Tools

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.

Using debugging helper classes

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

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.