Simplest Lazy Loading ListView Example in Android with data populated from a MySQL database using php.

Hello all…

You may have seen many implementations of Lazy Loading ListView.
Today I will show you my method to create Lazy Loading ListViews.

I dont know whether it can be any more simple than this.

In this I am using AsyncTask to download each image.

So we will start.

Here we have 6 classes.

1. MainPage – This is our main activity that loads the ListView.
2. GetDataFromDB – This class get the image urls and it’s description as a string from the DB server and return that string.
Then we will split that string to seperate the urls and description and then set it to listview.
3. MyCustomArrayAdapter – Custom adapter for the ListView.
4. Model _ this class creates the object to be set for the ListView for each row.
5. PbAndImage – This class has an imageView and ProgressBar to send to the Asynctask.
6. DownloadImageTask – This class Asynchronously downloads the image.

At last the PHP Script which simple echoes the string containing the URLS and description of the image.

Here is the PHP Script.

getImageUrlsAndDescription.php

<?php
// get these values from your DB.
echo 	"http://coderzheaven.com/sample_folder/android_1.png,ANDROID0 ## 
		http://coderzheaven.com/sample_folder/coderzheaven.png,ANDROID1 ## 
		http://coderzheaven.com/sample_folder/coderzheaven.png,ANDROID2 ## 
		http://coderzheaven.com/sample_folder/coderzheaven.png,ANDROID3 ## 
		http://coderzheaven.com/sample_folder/android_1.png,ANDROID4 ## 
		http://coderzheaven.com/sample_folder/coderzheaven.png,ANDROID5 ## 
		http://coderzheaven.com/sample_folder/coderzheaven.png,ANDROID6 ## 
		http://coderzheaven.com/sample_folder/android_1.png,ANDROID7 ## 
		http://coderzheaven.com/sample_folder/coderzheaven.png,ANDROID8 ## 
		http://coderzheaven.com/sample_folder/coderzheaven.png,ANDROID9";
?>

So we will start.

MainPage.java

package com.coderzheaven.lazyloadinglistwithphpconnection;

import java.util.ArrayList;
import java.util.List;
import android.app.ListActivity;
import android.app.ProgressDialog;
import android.os.Bundle;
import android.widget.ArrayAdapter;

public     class     MainPage    extends ListActivity {

	@Override
	protected void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);

		setContentView(R.   layout.    contacts_list);

		final List<Model> list = new ArrayList<Model>();
		
		/** This block is for getting the image url to download from the server **/
		final GetDataFromDB getvalues = new GetDataFromDB();
		
		final ProgressDialog dialog = ProgressDialog.show(MainPage.this,
				"", "Gettting values from DB", true);
		new    Thread   (new Runnable() {
			public void run() {
				String response = getvalues.getImageURLAndDesciptionFromDB();
				System.out.println("Response : " + response);
				
				dismissDialog(dialog);
				if (!response.equalsIgnoreCase("")) {
					if (!response.equalsIgnoreCase("error")) {
						dismissDialog(dialog);
						
						// Got the response, now split it to get the image Urls and description
						String all[] = response.split("##"); 
						for(int k = 0; k < all.length; k++){
							String urls_and_desc[] = all[k].split(","); //  urls_and_desc[0] contains image url and [1] -> description.
							list.add(get(urls_and_desc[1],urls_and_desc[0]));
						}
					}
					
				} else {
					dismissDialog(dialog);
				}
			}
		}).start();
		/*************************** GOT data from Server ********************************************/

		ArrayAdapter<Model> adapter = new MyCustomArrayAdapter(this, list);
		setListAdapter(adapter);
	}

	public void dismissDialog(final ProgressDialog dialog){
		runOnUiThread(new Runnable() {
			public void run() {
				dialog.dismiss();
			}
		});
	}
	private Model get(String s, String url) {
		return new Model(s, url);
	}

}

GetDataFromDB.java

package com.coderzheaven.lazyloadinglistwithphpconnection;

import org.apache.http.client.HttpClient;
import org.apache.http.client.ResponseHandler;
import org.apache.http.client.methods.HttpPost;
import org.apache.http.impl.client.BasicResponseHandler;
import org.apache.http.impl.client.DefaultHttpClient;

public class GetDataFromDB {

	public String getImageURLAndDesciptionFromDB() {
		try {

			HttpPost httppost;
			HttpClient httpclient;
			httpclient = new DefaultHttpClient();
			httppost = new HttpPost(
					"http://10.0.2.2/test/getImageUrlsAndDescription.php"); // change this to your URL.....
			ResponseHandler<String> responseHandler = new BasicResponseHandler();
			final String response = httpclient.execute(httppost,
					responseHandler);
			
			return response;

		} catch (Exception e) {
			System.out.println("ERROR : " + e.getMessage());
			return "error";
		}
	}
}

Model.java

package com.coderzheaven.lazyloadinglistwithphpconnection;

public class Model {
	 
    private String name;
    private String url;
    
    public Model(String name, String url) {
        this.name = name;
        this.url = url;
    }

	public String getName() {
		return name;
	}

	public void setName(String name) {
		this.name = name;
	}

	public String getURL() {
		return url;
	}

	public void setURL(String url) {
		this.url = url;
	}
}

MyCustomArrayAdapter.java

package com.coderzheaven.lazyloadinglistwithphpconnection;

import java.util.List;
import android.app.Activity;
import android.graphics.Color;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ArrayAdapter;
import android.widget.ImageView;
import android.widget.ProgressBar;
import android.widget.TextView;

public class MyCustomArrayAdapter extends ArrayAdapter<Model> {

	private final Activity context;
	private final List<Model> list;

	public MyCustomArrayAdapter(Activity context, List<Model> list) {
		super(context, R.layout.list_layout, list);
		this.context = context;
		this.list = list;
	}

	static class ViewHolder {
		protected TextView text;
		protected ImageView image;
		protected ProgressBar pb;
	}

	@Override
	public View getView(int position, View convertView, ViewGroup parent) {
		View view = null;
		if (convertView == null) {
			LayoutInflater inflator = context.getLayoutInflater();
			view = inflator.inflate(R.layout.list_layout, null);
			final ViewHolder viewHolder = new ViewHolder();
			viewHolder.text = (TextView) view.findViewById(R.id.label);
			viewHolder.text.setTextColor(Color.BLACK);
			viewHolder.image = (ImageView) view.findViewById(R.id.image);
			viewHolder.image.setVisibility(View.GONE);
			viewHolder.pb = (ProgressBar) view.findViewById(R.id.progressBar1);
			view.setTag(viewHolder);
		} else {
			view = convertView;
		}
		ViewHolder holder = (ViewHolder) view.getTag();
		holder.text.setText(list.get(position).getName());
		holder.image.setTag(list.get(position).getURL());
		holder.image.setId(position);
		PbAndImage pb_and_image = new PbAndImage();
		pb_and_image.setImg(holder.image);
		pb_and_image.setPb(holder.pb);
    	new DownloadImageTask().execute(pb_and_image);
		return view;
	}
}

PbAndImage.java

package com.coderzheaven.lazyloadinglistwithphpconnection;

import android.widget.ImageView;
import android.widget.ProgressBar;

public class PbAndImage {
	
	private ImageView img;
	private ProgressBar pb;

	public ImageView getImg() {
		return img;
	}

	public void setImg(ImageView img) {
		this.img = img;
	}

	public ProgressBar getPb() {
		return pb;
	}

	public void setPb(ProgressBar pb) {
		this.pb = pb;
	}

}

DownloadImageTask.java

package com.coderzheaven.lazyloadinglistwithphpconnection;

import java.io.InputStream;
import java.net.URL;
import com.coderzheaven.lazyloadinglistwithphpconnection.PbAndImage;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.graphics.Matrix;
import android.os.AsyncTask;
import android.view.View;
import android.widget.ImageView;
import android.widget.ProgressBar;

public class DownloadImageTask extends AsyncTask<PbAndImage, Void, Bitmap> {

	ImageView imageView = null;
	ProgressBar pb = null;

	protected Bitmap doInBackground(PbAndImage... pb_and_images) {
		this.imageView = (ImageView)pb_and_images[0].getImg();
		this.pb = (ProgressBar)pb_and_images[0].getPb();
		return getBitmapDownloaded((String) imageView.getTag());
	}

	protected void onPostExecute(Bitmap result) {
		System.out.println("Downloaded " + imageView.getId());
		imageView.setVisibility(View.VISIBLE); 
		pb.setVisibility(View.GONE);  // hide the progressbar after downloading the image.
		imageView.setImageBitmap(result); //set the bitmap to the imageview.
	}

	/** This function downloads the image and returns the Bitmap **/
	private Bitmap getBitmapDownloaded(String url) {
		System.out.println("String URL " + url);
		Bitmap bitmap = null;
		try {
			bitmap = BitmapFactory.decodeStream((InputStream) new URL(url)
					.getContent());
			bitmap = getResizedBitmap(bitmap, 50, 50);
			return bitmap;
		} catch (Exception e) {
			e.printStackTrace();
		}
		return bitmap;
	}
	
	/** decodes image and scales it to reduce memory consumption **/
	public Bitmap getResizedBitmap(Bitmap bm, int newHeight, int newWidth) {
        int width = bm.getWidth();
        int height = bm.getHeight();
        float scaleWidth = ((float) newWidth) / width;
        float scaleHeight = ((float) newHeight) / height;
        // CREATE A MATRIX FOR THE MANIPULATION
        Matrix matrix = new Matrix();
        // RESIZE THE BIT MAP
        matrix.postScale(scaleWidth, scaleHeight);
        // RECREATE THE NEW BITMAP
        Bitmap resizedBitmap = Bitmap.createBitmap(bm, 0, 0, width, height, matrix, false);
        return resizedBitmap;
    }
}

And the Most important thing – DONT FORGET TO ADD THE INTERNET PERMISSION ON YOUR MANIFEST FILE.

 <uses-permission android:name="android.permission.INTERNET"/>

These are the layout files.

contacts_list.xml

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:orientation="vertical"
    android:layout_margin="10dp" >
    
  <ListView
            android:id="@id/android:list"
            android:layout_width="fill_parent"
            android:layout_height="0dp"
            android:dividerHeight="1dp"
            android:cacheColorHint="#0000"
            android:clipToPadding="true"
            android:layout_margin="5dp"
            android:soundEffectsEnabled="true"
            android:scrollbars="none"
            android:layout_weight="1">
    </ListView>

</LinearLayout>

list_layout.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:gravity="center_vertical"
    android:orientation="horizontal">
    
    <ProgressBar
        android:id="@+id/progressBar1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content" />
    
     <ImageView 
        android:layout_width="wrap_content"
        android:layout_height="wrap_content" 
        android:layout_margin="10dp"
        android:id="@+id/image"
        android:contentDescription="@drawable/ic_launcher">        
    </ImageView>
    
    <TextView 
        android:text="@+id/label" 
        android:layout_width="wrap_content"
        android:layout_height="wrap_content" 
        android:id="@+id/label"
        android:layout_marginLeft="15dp"
        android:layout_marginTop="5dp"
        android:textStyle="bold"
        android:textSize="20sp">        
    </TextView>
   
</LinearLayout>

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