Thursday, July 8, 2010

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().

Load ListView in background AsyncTask

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=
"http://4.bp.blogspot.com/_C5a2qH8Y_jk/StYXDpZ9-WI/AAAAAAAAAJQ/sCgPx6jfWPU/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.

7 comments:

Robert said...

Its really worth mentioning that you need to add the "Uses Permission" "Internet" to the AndroidManifest.xml in order to get this code to work...

Android Er said...

Thx Robert, the notice about Permission is added.

homer said...

You share files using a site that has multiple viruses, exploits, and trojans when you try to download from there.
Don't be a horses ass - remove it jerk.

Android Er said...

hello homer,

Thx for your advise. I want to use other service also, some of my old files lost.

Any suggest? please let me know.

Android Ashish said...

Can show image and text without customize the adapter in listView ?
I mean just like simple ArrayList items are shown in List view without Customize ArrayAdapter

Android Er said...

Dear Android Ashish,

I have no idea to do so!

Antonio Cabanelas said...

Thank you, i was setting asyntask outside main class and get static reference issue (setListAdapter), must have a child from main, now works. :))