滚动到顶部自动加载数据的listview封装

package com.example.niehongtao.listviewdemo;

import android.content.Context;
import android.util.AttributeSet;
import android.view.View;
import android.widget.AbsListView;
import android.widget.ListView;

/**
* Created by niehongtao on 16/4/18.
*/
public class AutoLoadMoreListView extends ListView {
// 这个布尔变量是必须使用的，因为不然会访问多次网络，这个可以控制，防止访问多次网络
private boolean mIsLoading = false;
private OnLoadMoreListener mOnLoadMoreListener;
private View mHeaderView;

public AutoLoadMoreListView(Context context) {
super(context);
init(context);
}

public AutoLoadMoreListView(Context context, AttributeSet attrs) {
super(context, attrs);
init(context);
}

private void init(Context context) {
mHeaderView = View.inflate(context, R.layout.autoloadmorelistview_header, null);
super.addHeaderView(mHeaderView);
hideHeadView();
super.setOnScrollListener(mScrollListener);
}

private void hideHeadView() {
mIsLoading = false;
mHeaderView.setVisibility(View.GONE);
}

private void showHeadView() {
mIsLoading = true;
mHeaderView.setVisibility(View.VISIBLE);
}

/**
* 加载完数据，供外界调用
*/
public void onLoadMoreComplete() {
mIsLoading = false;
hideHeadView();
}

private OnScrollListener mScrollListener = new OnScrollListener() {
@Override
public void onScrollStateChanged(AbsListView view, int scrollState) {
//            if (scrollState == SCROLL_STATE_FLING || scrollState == SCROLL_STATE_TOUCH_SCROLL || scrollState == SCROLL_STATE_IDLE) {
//                // 是否到了第一个条目
//                if (view.getFirstVisiblePosition() == 0 && !mIsLoading && mOnLoadMoreListener != null) {
//                    showHeadView();
//                    mOnLoadMoreListener.onLoadMore();
//                }
//            }
}

@Override
public void onScroll(AbsListView view, int firstVisibleItem, int visibleItemCount, int totalItemCount) {
if (firstVisibleItem == 0 && !mIsLoading && mOnLoadMoreListener != null) {
showHeadView();
mOnLoadMoreListener.onLoadMore();
}
}
};

/**
* 加载更多数据的接口
*/
interface OnLoadMoreListener {
void onLoadMore();
}

public void setOnLoadMoreListener(OnLoadMoreListener onLoadMoreListener) {
mOnLoadMoreListener = onLoadMoreListener;
}

}

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:id="@+id/loading"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:gravity="center"
>

<ProgressBar
android:layout_width="wrap_content"
android:layout_height="wrap_content"
/>

</LinearLayout>

class MyAdapter extends BaseAdapter {
private List<String> contents;
private Context mContext;

public MyAdapter(List<String> contents, Context context) {
this.contents = contents;
mContext = context;
}

@Override
public int getCount() {
return contents.size();
}
@Override
public Object getItem(int position) {
return contents.get(position);
}

@Override
public long getItemId(int position) {
return position;
}

@Override
public View getView(int position, View convertView, ViewGroup parent) {
ViewHolder holder;
if(convertView == null){
convertView = LayoutInflater.from(mContext).inflate(R.layout.item, parent, false);
holder = new ViewHolder();
holder.tvContent = (TextView) convertView.findViewById(R.id.tvContent);
convertView.setTag(holder);
}else{
holder = (ViewHolder) convertView.getTag();
}
holder.tvContent.setText(contents.get(position));
return convertView;
}
class ViewHolder{
TextView tvContent;
}
}

public class MainActivity extends Activity {
private AutoLoadMoreListView listview;
private MyAdapter adapter;
private List<String>  contents;
private Handler handler = new Handler();

@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
initData();
listview = (AutoLoadMoreListView) findViewById(R.id.listview);
adapter = new MyAdapter(contents, this);
listview.setAdapter(adapter);
listview.setOnLoadMoreListener(new AutoLoadMoreListView.OnLoadMoreListener() {
@Override
public void onLoadMore() {
handler.postDelayed(new Runnable() {
@Override
public void run() {
load();
adapter.notifyDataSetChanged();
listview.setAdapter(adapter);
listview.setSelection(20);
listview.onLoadMoreComplete();
}
}, 1000);
}
});
}

protected void load() {
ArrayList<String> list = new ArrayList<>();
for(int i = 0; i < 20; i++) {  //每次加载20条数据
list.add("加载数据:::" + i);
}
contents.addAll(0, list);
}
private void initData() {
contents = new ArrayList<String>();
for(int i = 0; i < 20; i++){
contents.add("加载数据:::" + i);
}
}

}