am ba944ccd: Doc change: update screens support table and remove outdated density/size metrics.

page.title=Designing for Responsiveness

@jd:body

<p>It's possible to write code that wins every performance test in the world, but still sends users in a fiery rage when they try to use the application. These are the applications that aren't <em>responsive</em> enough &mdash; the ones that feel

sluggish, hang or freeze for significant periods, or take too long to process

input. </p>

<p>In Android, the system guards against applications that are insufficiently responsive for a period of time by displaying a dialog to the user, called the Application Not Responding (ANR) dialog. The user can choose to let the application continue, but the user won't appreciate having to act on this dialog every time he or she uses your application. So it's important to design responsiveness into your application, so that the system never has cause to display an ANR to the user. </p>

<div class="figure">

<img src="{@docRoot}images/anr.png" alt="Screenshot of ANR dialog box" width="240" height="320"/>

<p><strong>Figure 1.</strong> An ANR dialog displayed to the user.</p>

</div>

<p>Generally, the system displays an ANR if an application cannot respond to user input. For example, if an  application blocks on some I/O operation (frequently a network access), then the main application thread won't be able to process incoming user input events. After a time, the system concludes that the application has hung, and displays the ANR to give the user the option to kill it. 

<p>It's possible to write code that wins every performance test in the world,

but still sends users in a fiery rage when they try to use the application.

These are the applications that aren't <em>responsive</em> enough &mdash; the

ones that feel sluggish, hang or freeze for significant periods, or take too

long to process input. </p>

<p>In Android, the system guards against applications that are insufficiently

responsive for a period of time by displaying a dialog to the user, called the

Application Not Responding (ANR) dialog, shown at right in Figure 1. The user

can choose to let the application continue, but the user won't appreciate having

to act on this dialog every time he or she uses your application. It's critical

to design responsiveness into your application, so that the system never has

cause to display an ANR dialog to the user. </p>

<p>Generally, the system displays an ANR if an application cannot respond to

user input. For example, if an  application blocks on some I/O operation

(frequently a network access), then the main application thread won't be able to

process incoming user input events. After a time, the system concludes that the

application is frozen, and displays the ANR to give the user the option to kill

it. </p>

<p>Similarly, if your application spends too much time building an elaborate in-memory

structure, or perhaps computing the next move in a game, the system will 

sure these computations are efficient using the techniques above, but even the

most efficient code still takes time to run.</p>

<p>In both of these cases, the fix is usually to create a child thread, and do

<p>In both of these cases, the recommended approach is to create a child thread and do

most of your work there. This keeps the main thread (which drives the user

interface event loop) running, and prevents the system from concluding your code

interface event loop) running and prevents the system from concluding that your code

has frozen. Since such threading usually is accomplished at the class

level, you can think of responsiveness as a <em>class</em> problem. (Compare

this with basic performance, which was described above as a <em>method</em>-level

concern.)</p>

<div class="sidebox-wrapper">

<div class="sidebox">

<img src="{@docRoot}images/anr.png" width="240" height="320" alt="Screenshot of ANR dialog box">

<p style="margin-top:.5em;padding:.5em;">An ANR dialog displayed to the user.</p>

</div>

</div>

<p>This document discusses how the Android system determines whether an application is

not responding and provides guidelines for

ensuring that your application is responsive. </p>

<p>This document covers these topics: </p>

<ul>

    <li><a href="#anr">What Triggers ANR?</a></li>

    <li><a href="#avoiding">How to Avoid ANR</a></li>

    <li><a href="#reinforcing">Reinforcing Responsiveness</a></li>

</ul>

<p>This document describes how the Android system determines whether an

application is not responding and provides guidelines for ensuring that your

application stays responsive. </p>

<h2 id="anr">What Triggers ANR?</h2>

for a particular application when it detects one of the following

conditions:</p>

<ul>  

    <li>No response to an input event (e.g. key press, screen touch) within 5 seconds</li>

    <li>A {@link android.content.BroadcastReceiver BroadcastReceiver} hasn't finished executing within 10 seconds</li>

    <li>No response to an input event (e.g. key press, screen touch) 

    within 5 seconds</li>

    <li>A {@link android.content.BroadcastReceiver BroadcastReceiver} 

    hasn't finished executing within 10 seconds</li>

</ul>

<h2 id="avoiding">How to Avoid ANR</h2>

As you write your post, please do the following:

<ol>

<li><strong>Read

the <a href="http://source.android.com/discuss/android-discussion-groups-charter">mailing list charter</a></strong> that covers the community guidelines.

the <a href="http://source.android.com/community/groups-charter.html">mailing list charter</a></strong> that covers the community guidelines.

</li>

<li><strong>Select the most appropriate mailing list for your question</strong>. There are several different lists for

developers, described below.</li>