{"id":315,"date":"2010-10-31T20:01:00","date_gmt":"2010-10-31T20:01:00","guid":{"rendered":"http:\/\/www.javacodegeeks.com\/2012\/10\/android-full-app-part-4-performing-the-api-request-asynchronously-from-the-main-activity.html"},"modified":"2012-10-21T19:20:05","modified_gmt":"2012-10-21T19:20:05","slug":"android-full-app-part-4-asynchronous","status":"publish","type":"post","link":"https:\/\/www.javacodegeeks.com\/2010\/10\/android-full-app-part-4-asynchronous.html","title":{"rendered":"Android Full App, Part 4: Performing the API request asynchronously from the main activity"},"content":{"rendered":"

This is the fourth part of the \u201cAndroid Full Application Tutorial\u201d series<\/a>. The complete application aims to provide an easy way of performing movies\/actors searching over the internet. In the first part of the series (\u201cMain Activity UI\u201d<\/a>), we created the Eclipse project and set up a basic interface for the main activity of the application. In the second part (\u201cUsing the HTTP API\u201d<\/a>), we used the Apache HTTP client library in order to consume an external HTTP API and integrate the API’s searching capabilities into our application. In the third part (\u201cParsing the XML response\u201d<\/a>) we saw how to parse the XML response using Android’s built-in XML parsing capabilities. In this part, we will tie together the HTTP retriever and XML parser services in order to perform the API search request from our application’s main activity. The request will be executed asynchronously in a background thread in order to avoid blocking the main UI thread.<\/p>\n

On mobile applications development, one very important aspect of the application’s behavior is the smooth execution. The application’s response to user input should be quick and the whole experience should be smooth and snappy. Application responsiveness is very significant especially for the Android platform and Google has published some design guidelines<\/a> for that. This is the reason that we will have the application perform the searching operations in the background, meaning that those will execute in a thread other than the main UI thread.<\/p>\n

Despite the fact that internet connection rates on mobile devices have been tremendously improved over the last years, it still remains a fact that downloading data from the internet can be a time consuming operation. Thus, we don’t want to pause the main thread while the HTTP client waits for the data to be downloaded. Also note that stalling the main thread UI for more than five seconds will cause an \u201cApplication Not Responding\u201d (ANR) dialog to kick in and the user will be given the opportunity to kill your application. That is definitely not a feature to have.<\/p>\n

For that purpose, we are going to leverage the Android API and use the built in class named AsyncTask<\/a>. I have explained its usage in a previous post of mine (\u201cAndroid Reverse Geocoding with Yahoo API \u2013 PlaceFinder\u201d<\/a>) but in short, this class allows us to properly and easily use the UI thread. From the official documentation page<\/a>: \u201cAsyncTask <\/a>enables proper and easy use of the UI thread. This class allows to perform background operations and publish results on the UI thread without having to manipulate threads and\/or handlers\u201d.<\/p>\n

Before we begin writing the asynchronous code, we will first introduce some service classes which will be responsible for performing the HTTP requests, parsing the XML responses, create the corresponding model objects and returning those to the calling Activity. Those classes will extend the abstract base class named GenericSeeker with the following source code:<\/p>\n

package com.javacodegeeks.android.apps.moviesearchapp.services;\r\n\r\nimport java.net.URLEncoder;\r\nimport java.util.ArrayList;\r\n\r\npublic abstract class GenericSeeker<E> {\r\n    \r\n    protected static final String BASE_URL = \"http:\/\/api.themoviedb.org\/2.1\/\";    \r\n    protected static final String LANGUAGE_PATH = \"en\/\";\r\n    protected static final String XML_FORMAT = \"xml\/\";\r\n    protected static final String API_KEY = \"<YOUR_API_KEY_HERE>\";\r\n    protected static final String SLASH = \"\/\";\r\n    \r\n    protected HttpRetriever httpRetriever = new HttpRetriever();\r\n    protected XmlParser xmlParser = new XmlParser();\r\n    \r\n    public abstract ArrayList<E> find(String query);\r\n    public abstract ArrayList<E> find(String query, int maxResults);\r\n\r\n    public abstract String retrieveSearchMethodPath();\r\n    \r\n    protected String constructSearchUrl(String query) {\r\n        StringBuffer sb = new StringBuffer();\r\n        sb.append(BASE_URL);\r\n        sb.append(retrieveSearchMethodPath());\r\n        sb.append(LANGUAGE_PATH);\r\n        sb.append(XML_FORMAT);\r\n        sb.append(API_KEY);\r\n        sb.append(SLASH);\r\n        sb.append(URLEncoder.encode(query));\r\n        return sb.toString();\r\n    }\r\n    \r\n    public ArrayList<E> retrieveFirstResults(ArrayList<E> list, int maxResults) {\r\n        ArrayList<E> newList = new ArrayList<E>();\r\n        int count = Math.min(list.size(), maxResults);\r\n        for (int i=0; i<count; i++) {\r\n            newList.add(list.get(i));\r\n        }\r\n        return newList;\r\n    }\r\n\r\n}\r\n<\/pre>\n
The GenericSeeker class denotes that it is able to find results of a particular class and the extending classes will have to provide concrete implementations for the appropriate classes. The HttpRetriever and XmlParser objects from our previous tutorials will be used. Remember that the TMDb API<\/a> uses similar URLs for movies and person searching:
 
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