In this tutorial we are going to see how to use Android
AsyncTask. As we read from the Android Documentation :
- AsyncTask 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.
- AsyncTask is designed to be a helper class around
Handlerand does not constitute a generic threading framework. AsyncTasks should ideally be used for short operations (a few seconds at the most.) If you need to keep threads running for long periods of time, it is highly recommended you use the various APIs provided by the
java.util.concurrentpacakge such as
- An asynchronous task is defined by a computation that runs on a background thread and whose result is published on the UI thread. An asynchronous task is defined by 3 generic types, called
Result, and 4 steps, called
In this example we are going to load a web page in the backgroud and display it in a
WebView. We will notice that the UI thread still remains fast and responsive in other UI activities.
For this tutorial, we will use the following tools in a Windows 64-bit platform:
- JDK 1.7
- Eclipse 4.2 Juno
- Android SKD 4.2
1. Create a new Android Project
Open Eclipse IDE and go to File -> New -> Project -> Android -> Android Application Project. You have to specify the Application Name, the Project Name and the Package name in the appropriate text fields and then click Next.
In the next window make sure the “Create activity” option is selected in order to create a new activity for your project, and click Next. This is optional as you can create a new activity after creating the project, but you can do it all in one step.
Select “BlankActivity” and click Next.
You will be asked to specify some information about the new activity. In the Layout Name text field you have to specify the name of the file that will contain the layout description of your app. In our case the file
res/layout/main.xml will be created. Then, click Finish.
2. Create the main layout of the Application
res/layout/main.xml file :
And paste the following code :
<?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" > <Button android:id="@+id/btn" android:layout_width="match_parent" android:layout_height="wrap_content" android:onClick="readWebpage" android:text="Load Webpage" > </Button> <Button android:id="@+id/button1" android:layout_width="match_parent" android:layout_height="wrap_content" android:onClick="dummyFunc" android:text="Dummy Button" /> <WebView android:id="@+id/webView" android:layout_width="fill_parent" android:layout_height="fill_parent" /> </LinearLayout>
Now you may open the Graphical layout editor to preview the User Interface you created:
Now we have to write the code of the application. Use the Package Explorer to navigate to the Java file of the Activity you’ve created:
The code of this tutorial is pretty much self explanatory.
4. Run the application
This is the main screen of our Application:
Now, when you press the “Load Webpage” button, the AsyncTask will start downloading and loading the Web Page. But, meanwhile if whe press the “Dummy Button”, you will see that the UI remains responsive. As you can see the web pages is loading and the UI is fast and responsive:
After a little while:
Download Eclipse Project
This was an Android Timer Example. Download the Eclipse Project of this tutorial: AndroidAsyncTaskTutorial.zip
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