刷新实现原理

package com.zzw.testrefresh;

import java.util.ArrayList;

import android.app.Activity;
import android.os.Bundle;
import android.os.SystemClock;
import android.widget.AbsListView;
import android.widget.AbsListView.OnScrollListener;
import android.widget.ArrayAdapter;
import android.widget.ListView;

public class MainActivity extends Activity implements OnScrollListener {

private ArrayList<String> data;
private ArrayAdapter<String> adapter;

private int firstVisibleItem;
private int visibleItemCount;
private int totalItemCount;

@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);

data = new ArrayList<String>();
for (int i = 0; i < 20; i++) {
data.add("原有数据--" + i);
}

ListView mListView = (ListView) findViewById(R.id.listView);

adapter = new ArrayAdapter<String>(this, android.R.layout.simple_list_item_1, data);

mListView.setAdapter(adapter);

mListView.setOnScrollListener(this);
}

@Override
public void onScrollStateChanged(AbsListView view, int scrollState) {
if (OnScrollListener.SCROLL_STATE_IDLE == scrollState) {

if (firstVisibleItem == 0) {
addTop();
}

if (firstVisibleItem + visibleItemCount == totalItemCount) {
addBottom();
}

}
}

@Override
public void onScroll(AbsListView view, int firstVisibleItem, int visibleItemCount, int totalItemCount) {
this.firstVisibleItem = firstVisibleItem;
this.visibleItemCount = visibleItemCount;
this.totalItemCount = totalItemCount;
}

private void addTop() {
data.add(0, "头部添加数据--" + (totalItemCount + 1));
adapter.notifyDataSetChanged();
}

private void addBottom() {
data.add("尾部添加数据--" + (totalItemCount + 1));
adapter.notifyDataSetChanged();
}

}