Load ListView in background AsyncTask

Refer to the old exercise "ListView with icon loaded from internet", it's a time-consume task to load bitmap from internet. So the code is modified in this exercise, a AsyncTask is implemented to handle the ListView: the bitmap is loaded in background thread, and setListAdapter() in onPostExecute().



row.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:orientation="horizontal">
<ImageView
android:id="@+id/icon"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:src="@drawable/icon"/>
<TextView
android:id="@+id/weekofday"
android:layout_width="wrap_content"
android:layout_height="wrap_content"/>
</LinearLayout>

AndroidList.java

package com.exercise.AndroidList;

import java.io.IOException;
import java.io.InputStream;
import java.net.HttpURLConnection;
import java.net.URL;
import java.net.URLConnection;

import android.app.ListActivity;
import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.os.AsyncTask;
import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ArrayAdapter;
import android.widget.ImageView;
import android.widget.ListView;
import android.widget.TextView;
import android.widget.Toast;

public class AndroidList extends ListActivity {

public class backgroundLoadListView extends
  AsyncTask<Void, Void, Void> {

 @Override
 protected void onPostExecute(Void result) {
  // TODO Auto-generated method stub
  setListAdapter(new MyCustomAdapter(AndroidList.this, R.layout.row, month));
  Toast.makeText(AndroidList.this,
    "onPostExecute \n: setListAdapter after bitmap preloaded",
    Toast.LENGTH_LONG).show();
 }

 @Override
 protected void onPreExecute() {
  // TODO Auto-generated method stub
  Toast.makeText(AndroidList.this,
    "onPreExecute \n: preload bitmap in AsyncTask",
    Toast.LENGTH_LONG).show();
 }

 @Override
 protected Void doInBackground(Void... params) {
  // TODO Auto-generated method stub
  preLoadSrcBitmap();
  return null;
 }

}

String image_URL=
 "https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEi_XrtCc0R0Nb9-Rhs-ZLlzO5cQNjBGfJ1v0FOhDUMuqbaoYm2bR5q_CnBhSekmSnSacwunEspG-l3NBwMAvnf7CGhhSaoaQWtDHIB_snN1y7VtaV7eTDyz0bwqkcejwZ7rpEMTRTyalvxn/s1600-r/android.png";

public class MyCustomAdapter extends ArrayAdapter<String> {
 Bitmap bm;

 public MyCustomAdapter(Context context, int textViewResourceId,
   String[] objects) {
  super(context, textViewResourceId, objects);
  // TODO Auto-generated constructor stub
 
  bm = srcBitmap;
 }

 @Override
 public View getView(int position, View convertView, ViewGroup parent) {
  // TODO Auto-generated method stub
  //return super.getView(position, convertView, parent);
 
  View row = convertView;
 
  if(row==null){
   LayoutInflater inflater=getLayoutInflater();
   row=inflater.inflate(R.layout.row, parent, false);
  }
 
  TextView label=(TextView)row.findViewById(R.id.weekofday);
  label.setText(month[position]);
  ImageView icon=(ImageView)row.findViewById(R.id.icon);
 
  icon.setImageBitmap(bm);
 
  return row;
 }
}

Bitmap srcBitmap;
private void preLoadSrcBitmap(){
 BitmapFactory.Options bmOptions;
 bmOptions = new BitmapFactory.Options();
 bmOptions.inSampleSize = 1;
 srcBitmap = LoadImage(image_URL, bmOptions);
}

String[] month = {
  "January", "February", "March", "April",
  "May", "June", "July", "August",
  "September", "October", "November", "December"
  };

/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
 super.onCreate(savedInstanceState);
 //setContentView(R.layout.main);

 /*setListAdapter(new ArrayAdapter<String>(this,
       R.layout.row, R.id.weekofday, DayOfWeek));*/
 new backgroundLoadListView().execute();
}

@Override
protected void onListItemClick(ListView l, View v, int position, long id) {
 // TODO Auto-generated method stub
 //super.onListItemClick(l, v, position, id);
 String selection = l.getItemAtPosition(position).toString();
 Toast.makeText(this, selection, Toast.LENGTH_LONG).show();
}

private Bitmap LoadImage(String URL, BitmapFactory.Options options)
{     
 Bitmap bitmap = null;
 InputStream in = null;     
 try {
  in = OpenHttpConnection(URL);
  bitmap = BitmapFactory.decodeStream(in, null, options);
  in.close();
 } catch (IOException e1) {
 }

 return bitmap;               
}

private InputStream OpenHttpConnection(String strURL) throws IOException{
 InputStream inputStream = null;
 URL url = new URL(strURL);
 URLConnection conn = url.openConnection();

 try{
  HttpURLConnection httpConn = (HttpURLConnection)conn;
  httpConn.setRequestMethod("GET");
  httpConn.connect();
 
  if (httpConn.getResponseCode() == HttpURLConnection.HTTP_OK) {
   inputStream = httpConn.getInputStream(); 
  } 
 }
 catch (Exception ex){
 }

 return inputStream;
}
}

please note that in order to permit the App to access to internet, we have to grand it permission of "android.permission.INTERNET"; refer to the last exercise "Load ImageView with bitmap from internet"


Download the files.

Thank you for reading this article Load ListView in background AsyncTask With URL https://x-tutorials.blogspot.com/2010/07/load-listview-in-background-asynctask.html. Also a time to read the other articles.