Android Asynchronous Task Learning notes

Android asynchronous tasks can be very convenient to complete time-consuming operations and update the UI, unlike multithreading also take advantage of Message Queuing, sub-threads send messages to the main thread, the main thread to update the UI. In short, the Android asynchronous task to the multi-threaded interaction for further encapsulation, easy to use.

The following is the asynchronous task demo code:

Completes the asynchronous download picture, updates the interface.

Package Com.example.android_async_task2;import Java.io.bytearrayoutputstream;import Java.io.ioexception;import Java.io.inputstream;import Org.apache.http.httpentity;import Org.apache.http.httpresponse;import Org.apache.http.client.clientprotocolexception;import Org.apache.http.client.httpclient;import Org.apache.http.client.methods.httpget;import Org.apache.http.impl.client.defaulthttpclient;import Org.apache.http.util.entityutils;import Android.app.activity;import Android.app.progressdialog;import Android.graphics.bitmap;import Android.graphics.bitmapfactory;import Android.os.asynctask;import Android.os.bundle;import Android.view.menu;import Android.view.view;import Android.view.View.OnClickListener; Import Android.widget.button;import Android.widget.imageview;public class Mainactivity extends Activity {private Button btn=null;private ImageView image=null;private String image_path= "Http://f2.sjbly.cn/m13/0729/1459/6947edn_ 690x459_b.jpg ";p rivate progressdialog Dialog; @Overrideprotectedvoid OnCreate (Bundle savedinstancestate) {super.oncreate (savedinstancestate); Setcontentview (r.layout.activity_ Main), btn= (Button) This.findviewbyid (r.id.button1);d ialog=new progressdialog (this);d ialog.settitle ("hint message"); Dialog.setmessage ("Download, please wait ...");//Set the style of the progress bar Dialog.setprogressstyle (progressdialog.style_horizontal);// The screen does not lose focus dialog.setcancelable (false); image= (ImageView) This.findviewbyid (r.id.imageview1); Btn.setonclicklistener ( New Onclicklistener () {@Overridepublic void OnClick (View v) {new MyTask (). Execute (image_path);});} public class MyTask extends asynctask<string,integer,bitmap>{@Overrideprotected void OnPreExecute () { Dialog.show (); Super.onpreexecute ();} @Overrideprotected Bitmap doinbackground (String ... params) {//define a memory stream and do not need to close bytearrayoutputstream out= new Bytearrayoutputstream ();//define an input stream InputStream in=null; Bitmap bitmap=null;//through HttpClient class to obtain network resources HttpClient httpclient=new defaulthttpclient ();//Set Request method (note the request address URL to write!!!) ) HttpGet httpget=new HttpGet (params[0]); try {//Get request status HttpresPonse Httpresponse=httpclient.execute (HttpGet);//Determine request status result code if (Httpresponse.getstatusline (). Getstatuscode () ==200) {/*//entity httpentity httpentity=httpresponse.getentity () that gets a response through an entity class;//Gets the byte array of the entity through an Entity tool class Byte[]data= Entityutils.tobytearray (httpentity);//Create Bitmap object Bitmapfactory.decodebytearray (data, 0, Data.length) through the factory class; */// Gets the input stream in=httpresponse.getentity (). getcontent ();//Gets the total length of the file Long File_length=httpresponse.getentity (). Getcontentlength ();//Calculate total length int total_len=0;int len=0;byte[] buffer=new byte[1024];try{while ((len=in.read (buffer))! = -1) {Total_len+=len;<span style= "color: #ff0000;" >//Scale Calculation formula </span>int value= (int) (total_len/((float) file_length) *100) <span style= "color: #ff6666;" >//the scale of the progress bar is published </span>publishprogress (value);//write output stream out.write (buffer, 0, Len);} The memory output flows into byte array Bitmap=bitmapfactory.decodebytearray (Out.tobytearray (), 0, Out.tobytearray (). length);} catch (Exception e) {}finally{if (in!=null) {in.close ();}}}} catch (Clientprotocolexception e) {//TODO auto-generated catch BLOCKE.PRintstacktrace ();} catch (IOException e) {//TODO auto-generated catch Blocke.printstacktrace ();} return bitmap;} @Overrideprotected void OnPostExecute (Bitmap result) {Super.onpostexecute (result); Image.setimagebitmap (result); Dialog.dismiss ();} @Overrideprotected void Onprogressupdate (Integer ... values) {super.onprogressupdate (values);d ialog.setprogress ( Values[0]);}} @Overridepublic boolean Oncreateoptionsmenu (Menu menu) {//Inflate the menu; This adds items to the action bar if it is PR Esent.getmenuinflater (). Inflate (R.menu.main, menu); return true;}}

which

Publishprogress (value);

is the ability to send several objects to

The Onprogressupdate () method.

Demo Download: http://download.csdn.net/detail/u014600432/8175337

Android Asynchronous Task Learning notes