docs/html/guide/developing/debug-tasks.jd

page.title=Debugging Tasks
@jd:body

<div id="qv-wrapper">
<div id="qv">
  <h2>In this document</h2>
  <ol>
    <li><a href="#tools">Tools</a></li>
    <li><a href="#additionaldebugging">Debug and Test Settings</a></li>
    <li><a href="#toptips">Top Debugging Tips</a></li>
    <li><a href="#ide-debug-port">Configuring Your IDE to Attach to the Debugging Port</a></li>
  </ol>
</div>
</div>

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


<h2 id="tools">Tools</h2>
<p>The Android SDK includes a fairly extensive set of tools to help you debug your programs: </p>
<ul>
    <li><a href="{@docRoot}guide/developing/tools/ddms.html"><strong>DDMS</strong></a> - 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. </li>
    <li><strong><a href="{@docRoot}guide/developing/tools/ddms.html#logcat">logcat</a></strong> - 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.
        
    <pre>...
I/MemoryDealer( 763): MemoryDealer (this=0x54bda0): Creating 2621440 bytes heap at 0x438db000
<span style="background-color:#CCCCCC; border-bottom:medium">I/Logger( 1858): getView() requesting item number 0
I/Logger( 1858): getView() requesting item number 1
I/Logger( 1858): getView() requesting item number 2</span>
D/ActivityManager( 763): Stopping: HistoryRecord{409dbb20 com.android.home.AllApps}
...</pre>

    </li>
    <li><p><strong>{@link android.util.Log Android Log}</strong>- 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.</p>
        <p>To use the <code>Log</code> class, you just call <code>Log.v()</code>
        (verbose), <code>Log.d()</code> (debug), <code>Log.i()</code> (information), 
        <code>Log.w()</code> (warning) or <code>Log.e</code> (error) depending
        on the importance you wish to assign the log message.</p>
                <code>Log.i(&quot;MyActivity&quot;, &quot;MyClass.getView()
                &mdash; Requesting item number &quot; + position)</code>
        <p>You can use logcat to read these messages</p></li>
    <li><strong><a href="{@docRoot}guide/developing/tools/traceview.html">Traceview</a> </strong>- 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. </li>
</ul>
<ul>
    <li><a href="{@docRoot}guide/developing/eclipse-adt.html"><strong>Eclipse plugin</strong></a> - 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. </li>
    <li><strong>Debug and Test Device Settings</strong> - Android exposes several settings
        that expose useful information such as CPU usage and frame rate. See <a href="#additionaldebugging">Debug
        and Test Settings on the Emulator</a> below. </li>
</ul>
<p>Also, see the <a href="{@docRoot}guide/appendix/faq/troubleshooting.html">Troubleshooting</a> section
    of the doc to figure out why your application isn't appearing on the emulator,
    or why it's not starting. </p>


<h2 id="additionaldebugging">Debug and Test Settings</h2>

<p>With the <strong>Dev Tools</strong> 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
    <strong>Dev Tools</strong> application and open <strong>Development Settings</strong>.
    This will open the development settings page with the following options (among
    others):</p>
<ul>
    <li><strong>Debug app</strong>&nbsp;&nbsp;&nbsp;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:
        <ul>
                <li>It will prevent Android from throwing an error if you pause on
                    a breakpoint for a long time while debugging.</li>
            <li>It will enable you to select the <em>Wait for Debugger</em> option
                to pause application startup until your debugger attaches (described
                next). </li>
        </ul>
    </li>
    <li><strong>Wait for debugger </strong> &nbsp;&nbsp;
        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
            {@link android.os.Debug#waitForDebugger()} to your code. </li>
    <li><strong>Immediately destroy activities</strong>&nbsp;&nbsp;&nbsp;Tells the
        system to destroy an activity as soon as it is stopped (as if Android had to
        reclaim memory).&nbsp; This is very useful for testing the {@link android.app.Activity#onSaveInstanceState}
        / {@link android.app.Activity#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.</li>
    <li><strong>Show screen updates</strong>&nbsp;&nbsp;&nbsp;
        Flashes a momentary pink rectangle on any screen sections that are being
            redrawn. This is very useful for discovering unnecessary screen drawing. </li>
    <li><strong>Show CPU usage</strong>&nbsp;&nbsp;&nbsp;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. <em>Note: You cannot turn this feature off
        once it is on, without restarting the emulator.</em> </li>
    <li><strong>Show background</strong>&nbsp;&nbsp;&nbsp;Displays a background pattern
        when no activity screens are visible. This typically does not happen, but
        can happen during debugging. </li>
</ul>
<p>These settings will be remembered across emulator restarts. </p>

<h2 id="toptips">Top Debugging Tips</h2>
<!--
<ul>
    <li><a href="#stackdump">Quick stack dump</a></li>
    <li><a href="#displayinfo">Displaying useful info on the emulator screen </a></li>
    <li><a href="#dumpstate">Getting system state information from the emulator (dumpstate)</a></li>
    <li><a href="#dumpsys">Getting application state information from the emulator (dumpsys)</a></li>
    <li><a href="#radioinfo">Getting wireless connectivity information</a></li>
    <li><a href="#loggingdata">Logging Trace Data</a></li>
    <li><a href="#logradio">Logging  Radio Data </a></li>
    <li><a href="#adb">Running adb</a></li>
    <li><a href="#screencaps">Getting screen captures from the emulator</a></li>
    <li><a href="#debughelpers">Using debug helper classes</a></li>
</ul>
-->
<dl>
<dt>Quick stack dump <a name="stackdump" id="stackdump"></a></dt>
<dd>To obtain a stack dump from emulator, you can log
in with <code>adb shell</code>, use &quot;ps&quot; to find the process you
want, and then &quot;kill -3 &quot;. The stack trace appears in the log file.
</dd>

<dt>Displaying useful info on the emulator screen<a name="displayinfo" id="displayinfo"></a></dt>
<dd>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 <a href="#additionaldebugging">Setting debug and test
configurations on the emulator</a>.
</dd>

<dt>Getting system state information from the emulator (dumpstate)<a name="dumpstate" id="dumpstate"></a> </dt>
<dd>You can access dumpstate information from the Dalvik Debug Monitor Service
tool. See <a href="{@docRoot}guide/developing/tools/adb.html#dumpsys">dumpsys and
dumpstate</a> on the adb topic page.</dd>

<dt>Getting application state information from the emulator (dumpsys)<a name="dumpsys" id="dumpsys"></a></dt>
<dd>You can access dumpsys information from the Dalvik Debug Monitor Service
tool. See <a href="{@docRoot}guide/developing/tools/adb.html#dumpsys">dumpsys and
dumpstate</a> on the adb topic page.</dd>

<dt>Getting wireless connectivity information <a name="radioinfo" id="radioinfo"></a></dt>
<dd>You can get information about wireless connectivity using the Dalvik Debug
Monitor Service tool. From the <strong>Device</strong> menu, select &quot;Dump
radio state&quot;.</dd>

<dt>Logging Trace Data<a name="loggingdata" id="loggingdata"></a></dt>
<dd>You can log method calls and other tracing data in an activity by calling
android.os.Debug.startMethodTracing(). See <a
href="{@docRoot}guide/developing/tools/traceview.html">Running the Traceview Debugging
Program</a> for details. </dd>

<dt>Logging Radio Data<a name="logradio" id="logradio"></a></dt>
<dd>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:

<pre>
adb shell
logcat -b radio
</pre>
</dd>

<dt>Running adb<a name="adb" id="adb"></a></dt>
<dd>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 <a href="{@docRoot}guide/developing/tools/adb.html">Using adb</a> for details.</dd>

<dt>Getting screen captures from the emulator<a name="screencaps" id="screencaps"></a></dt>
<dd> Dalvik Debug Monitor Server (DDMS) can capture screenshots from the emulator.</dd>


<a name="debughelpers"></a>

<dt>Using debugging helper classes</dt>

<dd>Android provides debug helper classes such as {@link android.util.Log
    util.Log} and {@link android.os.Debug} for your convenience. </dd>
</dl>

<h2 id="ide-debug-port">Configuring Your IDE to Attach to the Debugging Port</h2>

<p>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.</p>
<p>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 &quot;Wait for debugger&quot; in the Development settings panel
    the application will run when Eclipse connects, so you will need to set any breakpoints
    you want before connecting.</p>
<p>Changing either the application being debugged or the &quot;Wait for debugger&quot;
    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.</p>