Update BaseAdapter in backgrond Thread, to insert Gallery items in run-time.

Refer to the last post "Implement a photo bar using android.widget.Gallery, with custom BaseAdapter, and custom object"; in some case such as the Gallery items have to be downloaded from internet, we cannot wait too long to load Gallery in UI thread.



We will modify the Java code in "Implement a photo bar using android.widget.Gallery, with custom BaseAdapter, and custom object", to implement a background Thread to insert Gallery items in a dummy delay of 500ms for each item, in run-time. After each item inserted, send a message from the thread to the handle in UI thread to call notifyDataSetChanged() to update the Gallery.

package com.AndroidPhotoBar;

import java.util.ArrayList;

import android.app.Activity;
import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.os.Bundle;
import android.os.Handler;
import android.os.Message;
import android.view.View;
import android.view.ViewGroup;
import android.widget.BaseAdapter;
import android.widget.Gallery;
import android.widget.ImageView;

public class AndroidPhotoBarActivity extends Activity {
 
 MyThread myThread;
 
 ArrayList<ImageItem> arrayImageItem;
 MyAdapter myAdapter;
 
   public class ImageItem {
    
    Bitmap bitmapImage;
    
    ImageItem(){
     //To simplify, we use a default image here
     bitmapImage = BitmapFactory.decodeResource(
       AndroidPhotoBarActivity.this.getResources(), R.drawable.icon);
    }
    
    public Bitmap getImage(){
     return bitmapImage;
    }
    
 }
  
   Gallery myPhotoBar;

 /** Called when the activity is first created. */
   @Override
   public void onCreate(Bundle savedInstanceState) {
       super.onCreate(savedInstanceState);
       setContentView(R.layout.main);
       myPhotoBar = (Gallery)findViewById(R.id.photobar);
      
       myAdapter = new MyAdapter(this); //init myAdapter without ImageItem
       myPhotoBar.setAdapter(myAdapter);
      
       myThread = new MyThread();
       myThread.setRunning(true);
       myThread.start();

   }
  
   private void insertDummyImageItem(int cnt){

    //Insert dummy ImageItem into myAdapter
    for(int i = 0; i < cnt; i++){
     myAdapter.addImageItem(new ImageItem());
    }

   }

   public class MyAdapter extends BaseAdapter {
    
    Context context;
    ArrayList<ImageItem> _arrayImageItem;
    
    MyAdapter(Context c){
     context = c;
     _arrayImageItem = new ArrayList<ImageItem>();
    }
    
    public void addImageItem(ImageItem item){
     _arrayImageItem.add(item);
    }

  public int getCount() {
   // TODO Auto-generated method stub
   return _arrayImageItem.size();
  }

  public Object getItem(int position) {
   // TODO Auto-generated method stub
   return _arrayImageItem.get(position);
  }

  public long getItemId(int position) {
   // TODO Auto-generated method stub
   return position;
  }

  public View getView(int position, View convertView, ViewGroup parent) {
   // TODO Auto-generated method stub
   ImageView imageView;
   imageView = new ImageView(context);
   
   imageView.setLayoutParams(new Gallery.LayoutParams(150, 150)); 
   imageView.setScaleType(ImageView.ScaleType.CENTER_CROP);
   imageView.setImageBitmap(_arrayImageItem.get(position).getImage());
   
   return imageView;
  }
 }
  
   public class MyThread extends Thread{
    volatile boolean running = false;
    int cnt;
    
    void setRunning(boolean b){
     running = b;
     cnt = 10; 
    }
    
  @Override
  public void run() {
   // TODO Auto-generated method stub
   while(running){
    try {
     sleep(500);
     insertDummyImageItem(1);
     handler.sendMessage(handler.obtainMessage());
     if(cnt-- == 0){
      running = false; 
     } 
    } catch (InterruptedException e) {
     e.printStackTrace();
     
    } 
   }
   
  }
    
   }
  
   Handler handler = new Handler(){

  @Override
  public void handleMessage(Message msg) {
   // TODO Auto-generated method stub
   myAdapter.notifyDataSetChanged();
  }
    
   };
}