样本意向服务

这是一个假装在后台加载图像的 IntentService 的例子。实现 IntentService 所需要做的就是提供一个调用 super(String) 构造函数的构造函数，并且需要实现 onHandleIntent(Intent) 方法。

public class ImageLoaderIntentService extends IntentService {

    public static final String IMAGE_URL = "url";

    /**
     * Define a constructor and call the super(String) constructor, in order to name the worker
     * thread - this is important if you want to debug and know the name of the thread upon 
     * which this Service is operating its jobs.
     */
    public ImageLoaderIntentService() {
        super("Example");
    }

    @Override
    protected void onHandleIntent(Intent intent) {
        // This is where you do all your logic - this code is executed on a background thread

        String imageUrl = intent.getStringExtra(IMAGE_URL);

        if (!TextUtils.isEmpty(imageUrl)) {
            Drawable image = HttpUtils.loadImage(imageUrl); // HttpUtils is made-up for the example
        }

        // Send your drawable back to the UI now, so that you can use it - there are many ways
        // to achieve this, but they are out of reach for this example
    }
}

要启动 IntentService，你需要发送一个 Intent。例如，你可以从 Activity 这样做。当然，你不仅限于此。这是一个如何从 Activity 类召唤你的新 Service 的例子。

Intent serviceIntent = new Intent(this, ImageLoaderIntentService.class); // you can use 'this' as the first parameter if your class is a Context (i.e. an Activity, another Service, etc.), otherwise, supply the context differently
serviceIntent.putExtra(IMAGE_URL, "http://www.example-site.org/some/path/to/an/image");
startService(serviceIntent); // if you are not using 'this' in the first line, you also have to put the call to the Context object before startService(Intent) here

IntentService 按顺序处理其 Intents 中的数据，这样你就可以发送多个 Intent 而无需担心它们是否会相互碰撞。一次只处理一个 Intent，其余的进入队列。当所有作业完成后，IntentService 将自动关闭。