C# Corner
Tech
News
Videos
Forums
Jobs
Books
Events
More
Interviews
Live
Learn
Training
Career
Members
Blogs
Challenges
Certification
Contribute
Article
Blog
Video
Ebook
Interview Question
Collapse
Feed
Dashboard
Wallet
Learn
Achievements
Network
Refer
Rewards
SharpGPT
Premium
Contribute
Article
Blog
Video
Ebook
Interview Question
Register
Login
AsyncTask Class in Android
WhatsApp
Amir Ali
5y
13.9k
0
0
100
Article
Introduction
This article explains the AsyncTask class in Android.
Asynctask
AsyncTask is a class used when a process takes time to complete. Suppose that when we want to load and transfer data to the web then we use the Asynctask class. The AsyncTask class provides some methods, such as doInBackGround(), onPreExecut(), onPostExecute() and onPorgressUpdate().
doInBackGround()
: This method is the one that takes time to complete. So when you perform a click operation of a button it calls execute() and then the doInBackGround() method will be called.
onPreExecute()
: This method is called before the doInBackGround() method is to run on the UI thread.
onPostExecute()
: This method is called after the doInBackGround() method runs on the UI thread. The result from the doInBackGround() method is ed to this method.
onProgressUpdate():
This method is called by the doInBackGround() method to publish progress to the UI thread.
Step 1
Create a project like this:
"New" -> "Android Application Project" then enter the application name and click "Next".
Click "Next".
Click "Next".
Step 2
Create an XML file with the following:
<?
xml
version
=
"1.0"
encoding
=
"utf-8"
?>
<
LinearLayout
xmlns:android
=
"http://schemas.android.com/apk/res/android"
android:layout_width
=
"match_parent"
android:layout_height
=
"match_parent"
android:orientation
=
"vertical"
android:background
=
"#123456"
>
<
Button
android:id
=
"@+id/button"
android:layout_width
=
"match_parent"
android:layout_height
=
"wrap_content"
android:onClick
=
"readWebpage"
android:text
=
"Load Webpage"
>
</
Button
>
<
TextView
android:id
=
"@+id/textView"
android:layout_width
=
"match_parent"
android:layout_height
=
"match_parent"
android:text
=
"Example Text"
>
</
TextView
>
</
LinearLayout
>
Step 3
I wrote the code which takes time inside doInBackground().
In doInBackGround the first step is to create a default HttpClient
HttpClient httpclient=new DefaultHttpClient(). After creating an Http Client we will instantiate a class to handle the post request and a URL as a parameter HttpGet httpget=new HttpGet(url). "url" is the URL that you want to invoke to send data. httppost.setEntitiy(new UrlEncodeFromEntity). The URL encoding is used to encode the parameter that you want to send. At last, we execute our request through the instance of the HttpClient and receive the response. HttpResponse httpResponse=httpclient.execute(httpget). For reading the response obtain an input stream and consume it reading data in this way:
Input Stream inputstream=httpResponse.getEntity().getContent()
Create a Java class file with the following:
package
com.asyntask;
import
java.io.BufferedReader;
import
java.io.InputStream;
import
java.io.InputStreamReader;
import
org.apache.http.HttpResponse;
import
org.apache.http.client.methods.HttpGet;
import
org.apache.http.impl.client.DefaultHttpClient;
import
android.app.Activity;
import
android.os.AsyncTask;
import
android.os.Bundle;
import
android.view.View;
import
android.widget.TextView;
public
class
MainActivity
extends
Activity
{
private
TextView txtView;
/** Called when the activity is first created. */
@Override
public
void
onCreate(Bundle savedInstanceState)
{
super
.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
txtView = (TextView) findViewById(R.id.textView);
}
private
class
DownloadWebPageTask
extends
AsyncTask < String, Void, String >
{
@Override
protected
String doInBackground(String...url1)
{
String response =
""
;
for
(String url: url1)
{
DefaultHttpClient defaultHttpClient =
new
DefaultHttpClient();
HttpGet httpGet =
new
HttpGet(url);
try
{
HttpResponse execute = defaultHttpClient.execute(httpGet);
InputStream inputStream = execute.getEntity().getContent();
BufferedReader buffer =
new
BufferedReader(
new
InputStreamReader(inputStream));
String st =
""
;
while
((st = buffer.readLine()) !=
null
)
{
response += st;
}
}
catch
(Exception e)
{
e.printStackTrace();
}
}
return
response;
}
@Override
protected
void
onPostExecute(String res)
{
txtView.setText(res);
}
}
public
void
readWebpage(View view)
{
DownloadWebPageTask task =
new
DownloadWebPageTask();
task.execute(
new
String[]
{
"http://www.google.com"
});
}
}
Step 4
Android Manifest.Xml file
In the Android Manifest.xml file you will provide the internet permission to connect to the internet as in the following:
<?
xml
version
=
"1.0"
encoding
=
"utf-8"
?>
<
manifest
xmlns:android
=
"http://schemas.android.com/apk/res/android"
package
=
"com.asyntask"
android:versionCode
=
"1"
android:versionName
=
"1.0"
>
<
uses-permission
android:name
=
"android.permission.INTERNET"
>
</
uses-permission
>
<
uses-sdk
android:minSdkVersion
=
"8"
android:targetSdkVersion
=
"18"
/>
<
application
android:allowBackup
=
"true"
android:icon
=
"@drawable/ic_launcher"
android:label
=
"@string/app_name"
android:theme
=
"@style/AppTheme"
>
<
activity
android:name
=
"com.asyntask.MainActivity"
android:label
=
"@string/app_name"
>
<
intent-filter
>
<
action
android:name
=
"android.intent.action.MAIN"
/>
<
category
android:name
=
"android.intent.category.LAUNCHER"
/>
</
intent-filter
>
</
activity
>
</
application
>
</
manifest
>
Android
AsyncTask
DefaulyHttpClient
HttpClient
Recommended related topics
Membership not found