實施異步任務

Question

我有一個RSS閱讀器在我的應用程序中工作。不過，我非常希望將線程從主I/O移開並使其成爲Async。

我真的被卡住了。

據我所知，這可以用幾條簡單的線條完成，但我對如何實現它感到困惑。

這是填充列表視圖的代碼： -

package co.uk.androidreader; 

import java.util.ArrayList; 
import java.util.HashMap; 
import java.util.Map; 

import org.w3c.dom.Document; 
import org.w3c.dom.Element; 
import org.w3c.dom.NodeList; 

import android.app.Activity; 
import android.content.Intent; 
import android.os.Bundle; 
import android.os.StrictMode; 
import android.view.View; 
import android.widget.AdapterView; 
import android.widget.AdapterView.OnItemClickListener; 
import android.widget.ListView; 

public class CustomizedListView extends Activity { 


Intent intent = getIntent(); 
// All static variables 
static final String URL = "URL of RSS Feed"; 
// XML node keys 
static final String KEY_ARTICLE = "article"; // parent node 
//static final String KEY_ID = "id"; 
static final String KEY_TITLE = "title"; 
static final String KEY_DATE = "date"; 
static final String KEY_STRAPLINE = "strapline"; 
static final String KEY_DETAIL = "detail"; 
static final String KEY_THUMB_URL = "image"; 



ListView list; 
LazyAdapter adapter; 

CustomizedListView thisReference = this; 

@Override 
public void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 
    setContentView(R.layout.main); 


    ArrayList<HashMap<String, String>> songsList = new ArrayList<HashMap<String, String>>(); 

    XMLParser parser = new XMLParser(); 
    String xml = parser.getXmlFromUrl(URL); // getting XML from URL 
    Document doc = parser.getDomElement(xml); // getting DOM element 

    NodeList nl = doc.getElementsByTagName(KEY_ARTICLE); 
    // looping through all song nodes <song> 
    for (int i = 0; i < nl.getLength(); i++) { 
     // creating new HashMap 
     HashMap<String, String> map = new HashMap<String, String>(); 
     Element e = (Element) nl.item(i); 
     // adding each child node to HashMap key => value 
     //map.put(KEY_ID, parser.getValue(e, KEY_ID)); 
     map.put(KEY_TITLE, parser.getValue(e, KEY_TITLE)); 
     map.put(KEY_DATE, parser.getValue(e, KEY_DATE)); 
     map.put(KEY_STRAPLINE, parser.getValue(e, KEY_STRAPLINE)); 
     map.put(KEY_DETAIL, parser.getValue(e, KEY_DETAIL)); 
     map.put(KEY_THUMB_URL, parser.getValue(e, KEY_THUMB_URL)); 


     // adding HashList to ArrayList 
     songsList.add(map); 
    } 


    list=(ListView)findViewById(R.id.list); 

    // Getting adapter by passing xml data ArrayList 
    adapter=new LazyAdapter(this, songsList);   
    list.setAdapter(adapter); 


    // Click event for single list row 
    list.setOnItemClickListener(new OnItemClickListener() { 
     @Override 
     public void onItemClick(AdapterView<?> parent, View view, int position, long id) { 

      Intent intent = new Intent(thisReference, DetailsActivity.class); 

      intent.putExtra(KEY_TITLE, (String) ((Map)adapter.getItem(position)).get(KEY_TITLE)); 
      intent.putExtra(KEY_DATE, (String) ((Map)adapter.getItem(position)).get(KEY_DATE)); 
      intent.putExtra(KEY_DETAIL, (String) ((Map)adapter.getItem(position)).get(KEY_DETAIL)); 

      startActivity(intent); 
     } 
    });  
} 

public void GoToHome(View v) 
{ 
     Intent myIntent = new Intent(CustomizedListView.this, MainActivity.class); 
     //myIntent.putExtra("communityName", (String)getIntent().getExtras().get(CustomizedListViewCommunity.KEY_NAME)); 
     startActivityForResult(myIntent, 0); 

} 

public void GoToBack(View v) 
{ 
     Intent myIntent = new Intent(CustomizedListView.this, MainActivity.class); 
     //myIntent.putExtra("communityName", (String)getIntent().getExtras().get(CustomizedListViewCommunity.KEY_NAME)); 
     startActivityForResult(myIntent, 0); 

} 

}

Answer 1

希望這有助於：

AsyncTask<String, Void, String> worker = new AsyncTask<String, Void, String>() { 

    @Override 
    protected String doInBackground(String... param) { 
     // here goes the code you want off the main thread 
     return "the result of this code that goes on onPostExecute"; 
    } 

    @Override 
    protected void onPostExecute(String str) { 
     super.onPostExecute(str); 

     // here goes the code that will run after you doInBackground has finished working 
    } 

}; 

worker.execute("any param you want"); 

Answer 2

任何網絡任務將無法在mainthread運行，所以我們需要一個asynctask。

class RequestTask extends AsyncTask<String, String, String>{ 



    @Override 
    protected String doInBackground(String... uri) { 
     HttpClient httpclient = new DefaultHttpClient(); 
     HttpResponse response; 
     String responseString = null; // THIS IS WHERE THE INFO IS SAVED 

     try { 
      response = httpclient.execute(new HttpGet(uri[0])); 
      StatusLine statusLine = response.getStatusLine(); 
      if(statusLine.getStatusCode() == HttpStatus.SC_OK){ 

       ByteArrayOutputStream out = new ByteArrayOutputStream(); 
       response.getEntity().writeTo(out); 
       out.close(); 
       responseString = out.toString("UTF-8"); 
      } 

      else{ 
       //Closes the connection. 
       response.getEntity().getContent().close(); 
       throw new IOException(statusLine.getReasonPhrase()); 
      } 
     } 

     catch (ClientProtocolException e) { 
      e.printStackTrace(); 

      //Handle httprequest when answer is not expected 
     } 

     catch (IOException e) { 
      e.printStackTrace(); 

      //Handle httprequest when answer is not expected 
     } 
     return responseString; 
    } 



    @Override 
    protected void onPostExecute(String result) { 
     super.onPostExecute(result); 
     progressDialog.dismiss(); 

       //handle your result here and any catches 



     }   









    } 




} 

然後使用 new RequestTask().execute("http://www.yourapilocation.com/whatever");要調用的方法。

希望這會有所幫助。

Answer 3

這裏是一個barbones實現onCreate方法的...

@Override 
public void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 
    setContentView(R.layout.main); 

    //define the task as an anonymous type (you could create a concrete inner class as well) 
    AsyncTask<Void, Void, ArrayList<HashMap<String,String>>> task = new AsyncTask<Void, Void, ArrayList<HashMap<String,String>>>() { 

     @Override 
     protected ArrayList<HashMap<String, String>> doInBackground(
       Void... params) { 
      ArrayList<HashMap<String, String>> songsList = new ArrayList<HashMap<String, String>>(); 

      XMLParser parser = new XMLParser(); 
      String xml = parser.getXmlFromUrl(URL); // getting XML from URL 
      Document doc = parser.getDomElement(xml); // getting DOM element 

      NodeList nl = doc.getElementsByTagName(KEY_ARTICLE); 
      // looping through all song nodes <song> 
      for (int i = 0; i < nl.getLength(); i++) { 
       // creating new HashMap 
       HashMap<String, String> map = new HashMap<String, String>(); 
       Element e = (Element) nl.item(i); 
       // adding each child node to HashMap key => value 
       //map.put(KEY_ID, parser.getValue(e, KEY_ID)); 
       map.put(KEY_TITLE, parser.getValue(e, KEY_TITLE)); 
       map.put(KEY_DATE, parser.getValue(e, KEY_DATE)); 
       map.put(KEY_STRAPLINE, parser.getValue(e, KEY_STRAPLINE)); 
       map.put(KEY_DETAIL, parser.getValue(e, KEY_DETAIL)); 
       map.put(KEY_THUMB_URL, parser.getValue(e, KEY_THUMB_URL)); 


       // adding HashList to ArrayList 
       songsList.add(map); 
      } 
      return songsList; 
     } 

     @Override 
     protected void onPostExecute(
       ArrayList<HashMap<String, String>> result) { 
      super.onPostExecute(result); 

      ListView list=(ListView)CustomizedListView.this.findViewById(R.id.list); 
      // Getting adapter by passing xml data ArrayList     
      list.setAdapter(new LazyAdapter(this, result)); 
     } 

    }; 

      //execute the task 
    task.execute((Void[])null); 

    list=(ListView)findViewById(R.id.list); 
    // Click event for single list row 
    list.setOnItemClickListener(new OnItemClickListener() { 
     @Override 
     public void onItemClick(AdapterView<?> parent, View view, int position, long id) { 

      Intent intent = new Intent(thisReference, DetailsActivity.class); 

      intent.putExtra(KEY_TITLE, (String) ((Map)adapter.getItem(position)).get(KEY_TITLE)); 
      intent.putExtra(KEY_DATE, (String) ((Map)adapter.getItem(position)).get(KEY_DATE)); 
      intent.putExtra(KEY_DETAIL, (String) ((Map)adapter.getItem(position)).get(KEY_DETAIL)); 

      startActivity(intent); 
     } 
    });  
}