original from:
http://blog.csdn.net/mayingcai1987/article/details/6273606
I added some personal note to the original code , so , just notice the notes as below:
package com.dynamic_load;
import android.app.Activity;
import android.app.ListActivity;
import android.os.Bundle;
import android.os.Handler;
import android.util.Log;
import android.view.Gravity;
import android.view.View;
import android.view.ViewGroup;
import android.widget.*;
import android.widget.AbsListView.OnScrollListener;
import android.widget.LinearLayout.LayoutParams;
public class DynamicLoadActivity extends ListActivity
{
private LinearLayout loadLayout;
private ListView listView;
private ListViewAdapter listViewAdapter=new ListViewAdapter();
private int lastItem=0;
private int maxCount=41;
private final Handler handler=new Handler();
private final LayoutParams progressBarLayoutParams=new LinearLayout.LayoutParams(
LinearLayout.LayoutParams.WRAP_CONTENT,
LinearLayout.LayoutParams.WRAP_CONTENT);
private final LayoutParams tipContentLayoutParams=new LinearLayout.LayoutParams(
LinearLayout.LayoutParams.WRAP_CONTENT,
LinearLayout.LayoutParams.WRAP_CONTENT);
private class ListViewAdapter extends BaseAdapter{
public int showCount=10;
public int getCount() {
// throw new UnsupportedOperationException("Not supported yet.");
//the total list count of the ListView
//triggered when an item appear and dispear;
//including appear on the view at the first time;
//return the total count of the appear item;
//ListView gets this count to appear the items;
// Log.i("l","get count:"+count);
return showCount;
}
public Object getItem(int position) {
// throw new UnsupportedOperationException("Not supported yet.");
// Log.i("l","get item:"+position);
return position;
}
public long getItemId(int position) {
// throw new UnsupportedOperationException("Not supported yet.");
//triggered when click an item;
//return the item id which was clicked;
// Log.i("l","get itemId:"+position);
return position;
}
//set the elements bar of the list view
public View getView(int position, View view, ViewGroup parent) {
// throw new UnsupportedOperationException("Not supported yet.");
// Log.i("l","get view:");
//return the view item to show up to the ListView to show;
//when a view is going to show up , ListView will trigger this
//function to render a view that it returned;
TextView textView;
if(view==null){
textView=new TextView(DynamicLoadActivity.this);
}
else {
textView=(TextView)view;
}
textView.setText("Item"+position);
textView.setTextSize(20f);
textView.setGravity(Gravity.CENTER);
textView.setHeight(60);
return textView;
}
}
private OnScrollListener onScrollListener=new OnScrollListener(){
public void onScrollStateChanged(AbsListView view, int scrollState) {
// throw new UnsupportedOperationException("Not supported yet.");
// Callback method to be invoked while the list view or grid view is being scrolled.
// If the view is being scrolled, this method will be called before the next frame
// of the scroll is rendered. In particular, it will be called before any calls to
// getView(int, View, ViewGroup).
// Parameters
// view The view whose scroll state is being reported
// scrollState The current scroll state. One of SCROLL_STATE_IDLE,
// SCROLL_STATE_TOUCH_SCROLL or SCROLL_STATE_IDLE.
//that means from still to scrolling, it will trigger once.
//or from scrolling to scroll,it will also trigger once.
Log.i("l","onScrollStateChanged");
if(lastItem==listViewAdapter.showCount //if lastItem==10;
&& scrollState==OnScrollListener.SCROLL_STATE_IDLE){ //&& the view is not scroll
if(listViewAdapter.showCount<=maxCount){
Runnable r=new Runnable(){
public void run() {
// throw new UnsupportedOperationException("Not supported yet.");
//since the count has been changed , and the count will be return to the
//ListView from OnScrollListener , so listener must notify the listView
//that something return to it has been changed, but not changed by
//ListView itself , but by the other classes;
listViewAdapter.showCount+=10;
//so this function must be followed the data that has been changed , which
//dosent changed by ListView itself;
listViewAdapter.notifyDataSetChanged();
listView.setSelection(lastItem);
}
};
handler.postDelayed(r, 1000);
}
}
}
public void onScroll(AbsListView view, int firstVisibleItem,
int visibleItemCount, int totalItemCount) {
// throw new UnsupportedOperationException("Not supported yet.");
// Callback method to be invoked when the list or grid has been scrolled.
// This will be called after the scroll has completed
// Parameters
// view The view whose scroll state is being reported
// firstVisibleItem the index of the first visible cell (ignore if visibleItemCount == 0)
// visibleItemCount the number of visible cells
// totalItemCount the number of items in the list adaptor
//that just means the view scrolling , it will trigger once on every frame
//when it is still. it will not trigger . Trigger only it is moving.
Log.i("l","onScroll");
Log.i("l","firstVisibleItem:"+firstVisibleItem);
Log.i("l","visibleItemCount:"+visibleItemCount);
//even only a little part is visible , will be calculate into the visibleItemCount;
//on opposite, only a part can't be seen copletely , that will be token out of the
//visibleItemCount;
//calculate every frame!
lastItem=firstVisibleItem+visibleItemCount-1;
if(listViewAdapter.showCount>maxCount){ //.count=10 original; maxCount=41;
listView.removeFooterView(loadLayout);
}
}
};
/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
// setContentView(R.layout.main);
//set the foot view of the list view
loadLayout=new LinearLayout(this);
loadLayout.setMinimumHeight(60);
loadLayout.setGravity(Gravity.CENTER);
loadLayout.setOrientation(LinearLayout.HORIZONTAL);
ProgressBar progressBar=new ProgressBar(this);
progressBar.setPadding(0,0,15,0);
loadLayout.addView(progressBar,progressBarLayoutParams);
TextView tipContent=new TextView(this);
tipContent.setText("Loading...");
loadLayout.addView(tipContent,tipContentLayoutParams);
//the footer view is not always show on the screen!
//it exists under the last item of the .getCount return;
listView=this.getListView();
listView.addFooterView(loadLayout);
this.setListAdapter(listViewAdapter);
listView.setOnScrollListener(onScrollListener);
}
}