sdk/installing/studio-debug.jd

page.title=Debugging with Android Studio

@jd:body

<div id="qv-wrapper">
<div id="qv">
<h2>In this document</h2>
<ol>
  <li><a href="#runDebug">Run your App in Debug Mode</a></li>
  <li><a href="#systemLog">Use the System Log</a>
    <ol>
      <li><a href="#systemLogWrite">Write log messages in your code</a></li>
      <li><a href="#systemLogView">View the system log</a></li>
    </ol>
  </li>
  <li><a href="#breakPoints">Work with Breakpoints</a>
    <ol>
        <li><a href="#breakPointsView">View and configure breakpoints</a></li>
        <li><a href="#breakPointsDebug">Debug your app with breakpoints</a></li>
    </ol>
  </li>
  <li><a href="#allocTracker">Track Object Allocation</a></li>
  <li><a href="#deviceMonitor">Analyze Runtime Metrics to Optimize your App</a></li>
  <li><a href="#screenCap">Capture Screenshots and Videos</a></li>
</ol>
<h2>See also</h2>
<ul>
<li><a href="{@docRoot}sdk/installing/studio-tips.html">
Android Studio Tips and Tricks</a></li>
<li><a href="{@docRoot}tools/debugging/index.html">Debugging</a></li>
<li><a href="{@docRoot}tools/help/monitor.html">Device Monitor</a></li>
<li><a href="{@docRoot}tools/debugging/ddms.html">Using DDMS</a></li>
</div>
</div>

<p>Android Studio enables you to debug apps running on the emulator or on an Android device.
With Android Studio, you can:</p>

<ul>
    <li>Select a device to debug your app on.</li>
    <li>View the system log.</li>
    <li>Set breakpoints in your code.</li>
    <li>Examine variables and evaluate expressions at run time.</li>
    <li>Run the debugging tools from the Android SDK.</li>
    <li>Capture screenshots and videos of your app.</li>
</ul>

<p>To debug your app, Android Studio builds a debuggable version of your app, connects
to a device or to the emulator, installs the app and runs it. The IDE shows the system log
while your app is running and provides debugging tools to filter log messages, work with
breakpoints, and control the execution flow.</p>


<h2 id="runDebug">Run your App in Debug Mode</h2>

<div class="figure" style="width:419px">
    <img src="{@docRoot}images/tools/as-debugdevices.png" alt=""/>
    <p class="img-caption"><strong>Figure 1.</strong> The Choose Device window enables you to
    select a physical Android device or a virtual device to debug your app.</p>
</div>

<p>To run your app in debug mode, you build an APK signed with a debug key and install it on a
physical Android device or on the Android emulator.
To set up an Android device for development, see <a href="{@docRoot}tools/device.html">Using
Hardware Devices</a>. For more information about the emulator provided by the Android SDK, see
<a href="{@docRoot}tools/devices/emulator.html">Using the Emulator.</a></p>

<p>To debug your app in Android Studio:</p>

<ol>
    <li>Open your project in Android Studio.</li>
    <li>Click <strong>Debug</strong> <img src="{@docRoot}images/tools/as-debugbutton.png"
        style="vertical-align:bottom;margin:0;height:22px"  alt=""/> in the toolbar.</li>
    <li>On the <em>Choose Device</em> window, select a hardware device from the list or
        choose a virtual device.</li>
    <li>Click <strong>OK</strong>. Your app starts on the selected device.</li>
</ol>

<p>Figure 1 shows the <em>Choose Device</em> window. The list shows all the Android devices
connected to your computer. Select <strong>Launch Emulator</strong> to use an Android virtual device
instead. Click the ellipsis <img src="{@docRoot}images/tools/as-launchavdm.png"
style="vertical-align:bottom;margin:0;height:19px" alt=""/> to open the
<a href="{@docRoot}tools/devices/managing-avds.html">Android Virtual Device Manager</a>.</p>

<p>Android Studio opens the <em>Debug</em> tool window when you debug your app. To open the
<em>Debug</em> window manually, click <strong>Debug</strong>
<img src="{@docRoot}images/tools/as-debugwindowbutton.png"
alt="" style="vertical-align:bottom;margin:0;height:20px"/>.
This window shows threads and variables in the <em>Debugger</em> tab, the device status in the
<em>Console</em> tab, and the system log in the <em>Logcat</em> tab. The <em>Debug</em> tool
window also provides other debugging tools covered in the following sections.</p>

<img src="{@docRoot}images/tools/as-debugview.png" alt="" />
<p class="img-caption"><strong>Figure 2.</strong> The Debug tool window in Android Studio showing
the current thread and the object tree for a variable.</p>


<h2 id="systemLog">Use the System Log</h2>

<p>The system log shows system messages while you debug your app. These messages include
information from apps running on the device. If you want to use the
system log to debug your app, make sure your code writes log messages and prints the stack
trace for exceptions while your app is in the development phase.</p>

<h3 id="systemLogWrite">Write log messages in your code</h3>

<p>To write log messages in your code, use the {@link android.util.Log} class. Log messages
help you understand the execution flow by collecting the system debug output while you interact
with your app. Log messages can tell you what part of your application failed. For more
information about logging, see <a href="{@docRoot}tools/debugging/debugging-log.html">
Reading and Writing Logs</a>.</p>

<p>The following example shows how you might add log messages to determine if previous state
information is available when your activity starts:</p>

<pre>
import android.util.Log;
...
public class MyActivity extends Activity {
    private static final String TAG = MyActivity.class.getSimpleName();
    ...
    &#64;Override
    public void onCreate(Bundle savedInstanceState) {
        if (savedInstanceState != null) {
            Log.d(TAG, "onCreate() Restoring previous state");
            /* restore state */
        } else {
            Log.d(TAG, "onCreate() No saved state available");
            /* initialize app */
        }
    }
}
</pre>

<p>During development, your code can also catch exceptions and write the stack trace to the system
log:</p>

<pre>
void someOtherMethod() {
    try {
        ...
    } catch (SomeException e) {
        Log.d(TAG, "someOtherMethod()", e);
    }
}
</pre>

<p class="note"><strong>Note:</strong> Remove debug log messages and stack trace print calls from
your code when you are ready to publish your app. You could do this by setting a <code>DEBUG</code>
flag and placing debug log messages inside conditional statements.</p>


<h3 id="systemLogView">View the system log</h3>

<p>Both the <em>Android DDMS</em> (Dalvik Debug Monitor Server) and the <em>Debug</em> tool windows
show the system log; however, the <em>Android DDMS</em> tool window lets you view only log messages
for a particular process. To view the system log on the <em>Android DDMS</em> tool window:</p>

<ol>
    <li>Start your app as described in <a href="#runDebug">Run your App in Debug Mode</a>.</li>
    <li>Click <strong>Android</strong> <img src="{@docRoot}images/tools/as-android.png" alt=""
        style="vertical-align:bottom;margin:0;height:20px"/> to open the <em>Android DDMS</em>
        tool window.</li>
    <li>If the system log is empty in the <em>Logcat view</em>, click <strong>Restart</strong>
        <img src="{@docRoot}images/tools/as-restart.png" alt=""
        style="vertical-align:bottom;margin:0;height:22px"/>.</li>
</ol>

<img src="{@docRoot}images/tools/as-ddmslog.png" alt="" />
<p class="img-caption"><strong>Figure 4.</strong> The system log in the Android DDMS tool
window.</p>

<p>The <em>Android DDMS</em> tool window gives you access to some DDMS features from Android Studio.
For more information about DDMS, see <a href="{@docRoot}tools/debugging/ddms.html">Using DDMS</a>.
</p>

<p>The system log shows messages from Android services and other Android apps. To filter the log
messages to view only the ones you are interested in, use the tools in the <em>Android DDMS</em>
window:</p>

<ul>
    <li>To show only log messages for a particular process, select the process in the
        <em>Devices</em> view and then click <strong>Only Show Logcat from Selected
        Process</strong> <img src="{@docRoot}images/tools/as-currentproc.png" alt=""
        style="vertical-align:bottom;margin:0;height:20px"/>. If the <em>Devices</em> view
        is not available, click <strong>Restore Devices View</strong>
        <img src="{@docRoot}images/tools/as-showdevview.png" alt=""
        style="vertical-align:bottom;margin:0;height:20px"/> on the right of the <em>Android
        DDMS</em> tool window. This button is only visible when you hide the <em>Devices</em>
        window.</li>
    <li>To filter log messages by log level, select a level under <em>Log Level</em> on the top
        of the <em>Android DDMS</em> window.</li>
    <li>To show only log messages that contain a particular string, enter the string in the search
        box and press <strong>Enter</strong>.</li>
</ul>


<h2 id="breakPoints">Work with Breakpoints</h2>

<p>Breakpoints enable you to pause the execution of your app at a particular line of code, examine
variables, evaluate expressions, and continue the execution line by line. Use breakpoints to
determine the causes of run-time errors that you can't fix by looking at your code only. To debug
your app using breakpoints:</p>

<ol>
    <li>Open the source file in which you want to set a breakpoint.</li>
    <li>Locate the line where you want to set a breakpoint and click on it.</li>
    <li>Click on the yellow portion of the side bar to the left of this line, as shown in figure 5.</li>
    <li>Start your app as described in <a href="#runDebug">Run your App in Debug Mode</a>.</li>
</ol>

<p>Android Studio pauses the execution of your app when it reaches the breakpoint. You can then
use the tools in the <em>Debug</em> tool window to identify the cause of the error.</p>

<img src="{@docRoot}images/tools/as-breakpointline.png" alt="" />
<p class="img-caption"><strong>Figure 5.</strong> A red dot appears next to the line when you set
a breakpoint.</p>

<h3 id="breakPointsView">View and configure breakpoints</h3>

<p>To view all the breakpoints and configure breakpoint settings, click <strong>View
Breakpoints</strong> <img src="{@docRoot}images/tools/as-viewbreakbutton.png" alt=""
style="vertical-align:bottom;margin:0;height:20px"/> on the left side of the <em>Debug</em> tool
window. The <em>Breakpoints</em> window appears, as shown in figure 6.</p>

<img src="{@docRoot}images/tools/as-breakpointswindow.png" alt="" />
<p class="img-caption"><strong>Figure 6.</strong> The Breakpoints window lists all the current
breakpoints and includes behavior settings for each.</p>

<p>The <em>Breakpoints</em> window lets you enable or disable each breakpoint from the
list on the left. If a breakpoint is disabled, Android Studio does not pause your app when
it hits that breakpoint. Select a breakpoint from the list to configure its settings.
You can configure a breakpoint to be disabled at first and have the system enable it after a
different breakpoint is hit. You can also configure whether a breakpoint should be disabled after
it is hit. To set a breakpoint for any exception, select <strong>Exception Breakpoints</strong>
in the list of breakpoints.</p>

<h3 id="breakPointsDebug">Debug your app with breakpoints</h3>

<p>After you set breakpoints in your code, click <strong>Rerun</strong>
<img src="{@docRoot}images/tools/as-restart.png" alt=""
style="vertical-align:bottom;margin:0;height:20px"/> to start the app again. When a breakpoint is
hit, Android Studio pauses the app and highlights the breakpoint in the source code. The
<em>Debug</em> tool window lets you examine variables and control the execution step by
step:</p>

<ul>
    <li>
        <p>To examine the object tree for a variable, expand it in the <em>Variables</em> view. If
        the <em>Variables</em> view is not visible, click <strong>Restore Variables View</strong>
        <img src="{@docRoot}images/tools/as-varviewbutton.png" alt=""
        style="vertical-align:bottom;margin:0;height:20px"/>.</p>
    </li>
    <li>
        <p>To evaluate an expression at the current execution point, click <strong>Evaluate
        Expression</strong> <img src="{@docRoot}images/tools/as-evalexpbutton.png" alt=""
        style="vertical-align:bottom;margin:0;height:20px"/>.</p>
    </li>
    <li>
        <p>To advance to the next line in the code (without entering a method), click <strong>Step
        Over</strong> <img src="{@docRoot}images/tools/as-stepoverbutton.png" alt=""
        style="vertical-align:bottom;margin:0;height:20px"/>.</p>
    </li>
    <li>
        <p>To advance to the first line inside a method call, click <strong>Step
        Into</strong> <img src="{@docRoot}images/tools/as-stepintobutton.png" alt=""
        style="vertical-align:bottom;margin:0;height:20px"/>.</p>
    </li>
    <li>
        <p>To advance to the next line outside the current method, click <strong>Step
        Out</strong> <img src="{@docRoot}images/tools/as-stepoutbutton.png" alt=""
        style="vertical-align:bottom;margin:0;height:20px"/>.</p>
    </li>
    <li>
        <p>To continue running the app normally, click <strong>Resume Program</strong>
        <img src="{@docRoot}images/tools/as-resumeprogrambutton.png" alt=""
        style="vertical-align:bottom;margin:0;height:20px"/>.</p>
    </li>
</ul>

<img src="{@docRoot}images/tools/as-variablesview.png" alt="" />
<p class="img-caption"><strong>Figure 7.</strong> The Variables view in the Debug tool window.</p>


<h2 id="allocTracker">Track Object Allocation</h2>

<p>Android Studio lets you track objects that are being allocated on the Java heap and see which
classes and threads are allocating these objects. This allows you to see the list of objects
allocated during a period of interest. This information is valuable for assessing memory usage
that can affect application performance.</p>

<p>To track memory allocation of objects:</p>

<ol>
<li>Start your app as described in <a href="#runDebug">Run Your App in Debug Mode</a>.</li>
<li>Click <strong>Android</strong> <img src="{@docRoot}images/tools/as-android.png" alt=""
style="vertical-align:bottom;margin:0;height:20px"/> to open the <em>Android DDMS</em>
tool window.</li>
<li>On the <em>Android DDMS</em> tool window, select the <strong>Devices | logcat tab</strong>.</li>
<li>Select your device from the dropdown list.</li>
<li>Select your app by its package name from the list of running apps.</li>
<li>Click <strong>Start Allocation Tracking</strong>
<img src="{@docRoot}images/tools/as-allocstart.png" alt=""
style="vertical-align:bottom;margin:0;height:20px"/></li>
<li>Interact with your app on the device.</li>
<li>Click <strong>Stop Allocation Tracking</strong>
<img src="{@docRoot}images/tools/as-allocstop.png" alt=""
style="vertical-align:bottom;margin:0;height:20px"/></li>
</ol>

<p>Android Studio shows the objects that the system allocated with the following information:</p>

<ul>
<li>Allocation order</li>
<li>Allocated class</li>
<li>Allocation size</li>
<li>Thread ID</li>
<li>Allocation method, class, and line number</li>
<li>Stack trace at the point of allocation</li>
</ul>

<img src="{@docRoot}images/tools/as-alloctrack.png" alt="" width="750" height="252" />
<p class="img-caption"><strong>Figure 8.</strong> Object allocation tracking in Android Studio.</p>


<h2 id="deviceMonitor">Analyze Runtime Metrics to Optimize your App</h2>

<p>Even if your application does not generate runtime errors, this does not mean it is free of
problems. You should also consider the following issues:</p>

<ul>
    <li>Does your app use memory efficiently?</li>
    <li>Does your app generate unnecessary network traffic?</li>
    <li>What methods should you focus your attention on to improve the performance of your app?</li>
    <li>Does your app behave properly when the user receives a phone call or a message?</li>
</ul>

<p>The Android Device Monitor is a stand-alone tool with a graphical user interface for serveral
Android application debugging and analysis tools, including the Dalvik Debug Monitor Server (DDMS).
You can use the Android Device Monitor to analyze memory usage, profile methods,
monitor network traffic and simulate incoming calls and messages.</p>

<p>To open the Android Device Monitor from Android Studio, click
<strong>Monitor</strong> <img src="{@docRoot}images/tools/as-monitorbutton.png" alt=""
style="vertical-align:bottom;margin:0;height:20px"/> on the toolbar. The Android Device Monitor
opens in a new window.</p>

<p>For more information about the Android Device Monitor and DDMS, see
<a href="{@docRoot}tools/help/monitor.html">Device Monitor</a> and
<a href="{@docRoot}tools/debugging/ddms.html">Using DDMS</a>.</p>


<h2 id="screenCap">Capture Screenshots and Videos</h2>

<p>Android Studio enables you to capture a screenshot or a short video of the device screen
while your app is running. Screenshots and videos are useful as promotional materials for your
app, and you can also attach them to bug reports that you send to your development team.</p>

<p>To take a screenshot of your app:</p>

<ol>
    <li>Start your app as described in <a href="#runDebug">Run your App in Debug Mode</a>.</li>
    <li>Click <strong>Android</strong> <img src="{@docRoot}images/tools/as-android.png" alt=""
        style="vertical-align:bottom;margin:0;height:20px"/> to open the <em>Android DDMS</em>
        tool window.</li>
    <li>Click <strong>Screen Capture</strong> <img src="{@docRoot}images/tools/as-capture.png"
        style="vertical-align:bottom;margin:0;height:22px" alt=""/> on the left side of the
        <em>Android DDMS</em> tool window.</li>
    <li>Optional: To add a device frame around your screenshot, enable the <em>Frame screenshot</em>
        option.</li>
    <li>Click <strong>Save</strong>.</li>
</ol>

<p>To take a video recording of your app:</p>

<ol>
    <li>Start your app as described in <a href="#runDebug">Run your App in Debug Mode</a>.</li>
    <li>Click <strong>Android</strong> <img src="{@docRoot}images/tools/as-android.png" alt=""
        style="vertical-align:bottom;margin:0;height:20px"/> to open the <em>Android DDMS</em>
        tool window.</li>
    <li>Click <strong>Screen Record</strong> <img src="{@docRoot}images/tools/as-record.png"
        style="vertical-align:bottom;margin:0;height:22px" alt=""/> on the left side of the
        <em>Android DDMS</em> tool window.</li>
    <li>Click <strong>Start Recording</strong>.</li>
    <li>Interact with your app.</li>
    <li>Click <strong>Stop Recording</strong>.</li>
    <li>Enter a file name for the recording and click <strong>OK</strong>.</li>
</ol>