am 7986a167: Merge "Cherry-pick 97432e86 to froyo." into froyo

page.title=Hello, World

@jd:body

<div id="qv-wrapper">

<div id="qv">

    <h2>In this document</h2>

    <ol>

      <li><a href="#platform">Install a Platform</a></li>

      <li><a href="#avd">Create an AVD</a></li>

      <li><a href="#create">Create the Project</a></li>

      <li><a href="#ui">Construct the UI</a></li>

great plugin that handles your project creation and management to greatly speed-up your

development cycles.</p>

<p>If you're not using Eclipse, that's okay. Familiarize yourself with 

<p>This tutorial assumes that you're using Eclipse. If you're not, see 

<a href="{@docRoot}guide/developing/other-ide.html">Developing in Other IDEs</a>.

You can then return to this tutorial and ignore anything about Eclipse.</p>

<p>Before you start, you should already have the very latest SDK installed, and if you're using

Eclipse, you should have installed the ADT plugin as well. If you have not installed these, see 

<a href="{@docRoot}sdk/installing.html">Installing the Android SDK</a> and return

here when you've completed the installation.</p>

<p>Before you start, you should already have the SDK installed, and if you're

using Eclipse, you should have installed the ADT plugin as well. If you have not

installed these, see <a href="{@docRoot}sdk/installing.html">Installing the

Android SDK</a> and return here when you've completed the installation.</p>

<h2 id="platform">Install a Platform</h2>

<p>To run the Hello World application, you need to install at least one Android

platform in your SDK environment. If you have not already performed this step,

you need to do it now.</p>

<p>To install a platform in Eclipse:</p>

<ol>

  <li>In the Android SDK and AVD Manager, choose <strong>Available

Packages</strong> in the left panel.</li> 

<li>Click the repository site checkbox to display the components

available for installation.</li>

  <li>Select at least one platform to install, and click <strong>Install

Selected</strong>. If you aren't sure which platform to install, use the latest

version.</li>

</ol>

<h2 id="avd">Create an AVD</h2>

Android Virtual Device (AVD). An AVD defines the system image and

device settings used by the emulator.</p>

<p>To create an AVD, use the "android" tool provided in the Android SDK.

Open a command prompt or terminal, navigate to the 

<code>tools/</code> directory in the SDK package and execute:

<pre>

android create avd --target 2 --name my_avd

</pre>

<p>The tool now asks if you would like to create a custom hardware profile.

For the time being, press Return to skip it ("no" is the default response). 

That's it. This configures an AVD named "my_avd" that uses the Android 1.5

platform. The AVD is now ready for use in the emulator.</p>

<p>In the above command, the <code>--target</code> option is required 

and specifies the deployment target to run on the emulator.

The <code>--name</code> option is also required and defines the 

name for the new AVD.</p>

<p>To create an AVD:</p>

<ol>

  <li>In Eclipse, choose <strong>Window &gt; Android SDK and AVD Manager</strong>. 

  <li>Select <strong>Virtual Devices</strong> in the left panel.</li>

  <li>Click <strong>New</strong>. </li>

<p>The <strong>Create New AVD</strong> dialog appears.</p>

  <li>Type the name of the AVD, such as "my_avd".</li>

  <li>Choose a target. The target is the platform (that is, the version of the Android

    SDK, such as 2.1) you want to run on the emulator. </li>

  <p>You can ignore the rest of the fields for now. </p>

  <li>Click <strong>Create AVD</strong>.</li>

</ol>

<h2 id="create">Create a New Android Project</h2>

<p>After you've created an AVD, the next step is to start a new

          <li><em>Application name:</em> Hello, Android</li>

          <li><em>Package name:</em> com.example.helloandroid (or your own private namespace)</li>

          <li><em>Create Activity:</em> HelloAndroid</li>

          <li><em>Min SDK Version:</em> 2</li>

        </ul>

        <p>Click <strong>Finish</strong>.</p>

                  reside under. This also sets the package name under which the stub

                  Activity will be generated.

                  <p>Your package name must be unique across

                  all packages installed on the Android system; for this reason, it's very

                  all packages installed on the Android system; for this reason, it's 

                  important to use a standard domain-style package for your

                  applications.  The example above uses the "com.example" namespace, which is

                  a namespace reserved for example documentation —

                chooses, but it doesn't need to. As the checkbox suggests, this is optional, but an

                Activity is almost always used as the basis for an application.</dd>

            <dt><em>Min SDK Version</em></dt>

                <dd>This value specifies the minimum API Level required by your application. If the API Level

                entered here matches the API Level provided by one of the available targets, 

                then that Build Target will be automatically selected (in this case, entering 

                "2" as the API Level will select the Android 1.1 target). With each new

                version of the Android system image and Android SDK, there have likely been 

                additions or changes made to the APIs. When this occurs, a new API Level is assigned

                to the system image to regulate which applications are allowed to be run. If an

                application requires an API Level that is <em>higher</em> than the level supported 

                by the device, then the application will not be installed.</dd>

                <dd>This value specifies the minimum API Level required by your application. For

                more information, see <a href="{@docRoot}guide/appendix/api-levels.html">Android API Levels</a>.

               </dd>

        </dl>

        <p><em>Other fields</em>: The checkbox for "Use default location" allows you to change 

pass <code>this</code> as your Context reference to the TextView.</p>

<p>Next, you define the text content with 

{@link android.widget.TextView setText(CharSequence) setText()}.</p>

{@link android.widget.TextView#setText(CharSequence) setText()}.</p>

<p>Finally, you pass the TextView to

{@link android.app.Activity#setContentView(View) setContentView()} in order to

<h2 id="run">Run the Application</h2>

<p>The Eclipse plugin makes it very easy to run your applications:</p>

<p>The Eclipse plugin makes it easy to run your applications:</p>

<ol>

  <li>Select <strong>Run > Run</strong>.</li>

UI layout. This means that you constructed and built your application's UI

directly in source code. If you've done much UI programming, you're

probably familiar with how brittle that approach can sometimes be: small

changes in layout can result in big source-code headaches. It's also very

changes in layout can result in big source-code headaches. It's also

easy to forget to properly connect Views together, which can result in errors in

your layout and wasted time debugging your code.</p>

(this example, however, is just one View element). You can use the

name of any class that extends {@link android.view.View} as an element in your XML layouts,

including custom View classes you define in your own code. This

structure makes it very easy to quickly build up UIs, using a more simple

structure makes it easy to quickly build up UIs, using a more simple

structure and syntax than you would use in a programmatic layout. This model is inspired

by the web development model, wherein you can separate the presentation of your

application (its UI) from the application logic used to fetch and fill in data.</p>