正文
Android 自定义ListView动态加载数据
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我们都知道网络取数据是耗时操作，如果我们一次性请求所有数据，假如数据量不多那还可以接受，但是如果数据量特别多，那么带来的后果就是用户的愤怒（用户是很没有耐心的），所以这时候我们就需要动态的加载数据，分批加载我们所需的数据，提升用户体验，先上图。
一般如果一个Activity集成越多的功能，代码量也会随之增多，看起来让人烦，我们可以考虑自定义控件将一些操作集成进去。
自定义ListView
package com.example.listviewdynamicloading; import android.content.Context;
import android.util.AttributeSet;
import android.view.LayoutInflater;
import android.view.View;
import android.widget.AbsListView;
import android.widget.AbsListView.OnScrollListener;
import android.widget.ListView; public class ZdyListView extends ListView implements OnScrollListener {
private int totalItemCount;// 总数量；
private int lastVisibleItem;// 最后一个可见的item；
private boolean isLoading;
private View footer;
private LayoutInflater inflater;
public RefleshDatas refleshDatas; public ZdyListView(Context context) {
super(context);
initView(context);
} public ZdyListView(Context context, AttributeSet attrs) {
super(context, attrs);
initView(context);
} public ZdyListView(Context context, AttributeSet attrs, int defStyle) {
super(context, attrs, defStyle);
initView(context);
} private void initView(Context context) {
footer=inflater.from(context).inflate(R.layout.layout_util_footer, null);
this.setOnScrollListener(this);
this.addFooterView(footer);
this.removeFooterView(footer);
} @Override
public void onScroll(AbsListView view, int firstVisibleItem,
int visibleItemCount, int totalItemCount) {
this.lastVisibleItem = firstVisibleItem + visibleItemCount;
this.totalItemCount = totalItemCount;
} @Override
public void onScrollStateChanged(AbsListView view, int scrollState) {
//listview item总数量等于最后一个可见的item并且ListView停下不动了
if (totalItemCount == lastVisibleItem&& scrollState == SCROLL_STATE_IDLE) {
if (!isLoading) {
isLoading = true;
this.addFooterView(footer);
if (refleshDatas != null) {
//回调执行向服务器端请求数据
refleshDatas.onLoading();
}
}
}
};
public void loadComplete() {
isLoading = false;
this.removeFooterView(footer);//加载完毕，移除footView；
}
public void setInterface(RefleshDatas refleshDatas) {
this.refleshDatas = refleshDatas;
}
public interface RefleshDatas{
public void onLoading();
}
}
MainActivity
package com.example.listviewdynamicloading; import java.util.ArrayList; import com.example.listviewdynamicloading.ZdyListView.RefleshDatas; import android.app.Activity;
import android.os.Bundle;
import android.os.Handler;
import android.os.Message;
import android.view.Menu;
import android.view.MenuItem;
import android.widget.ListView;
import android.widget.Toast; public class MainActivity extends Activity{
//一次从服务器端请求十条数据
private int current=1;
private int number=9; private ZdyListView listView; //自定义ListView，将footview，滑动监听等集合在一起，免得Activity代码过多
private ArrayList<String> listDatas;
private ListViewAdapter adapter; private Handler handler=new Handler(){
public void handleMessage(android.os.Message msg) {
switch (msg.what) {
case 0x123:
setlistView((ArrayList<String>)msg.obj,"firstLoading");//firstLoading标志位代表数据是初次加载的
break;
case 0x234:
setlistView((ArrayList<String>)msg.obj,"addLoading");//addLoading标志位代表数据是初次加载之后请求服务器所得
break;
case 0x345:
showMsg((String)msg.obj);
break;
default:
break;
}
};
}; @Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
listDatas=new ArrayList<String>();
listView=(ZdyListView) this.findViewById(R.id.listview);
listView.setInterface(new RefleshDatas() {
@Override
public void onLoading() {
getDataThread(current, current+number, "addLoading");
}
});
} @Override
protected void onStart() {
super.onStart();
getDataThread(current,number,"firstLoading");
} //.........................模拟开启线程向服务器请求数据.....................................
private void getDataThread(final int current, final int number,final String type) {
final Message msg=new Message();
new Thread(){
public void run() {
ArrayList<String> datas=ListViewDatas.returnNum(current, current+number);
if(datas!=null&&datas.size()>0){
switch (type) {
case "firstLoading":
msg.what=0x123;
break;
case "addLoading":
msg.what=0x234;
break;
default:
break;
}
msg.obj=datas;
}else {
msg.what=0x345;
msg.obj=datas;
}
handler.sendMessage(msg);
};
}.start();
} private void setlistView(ArrayList<String> datas,String type) {
listDatas.addAll(datas);
if(type.equals("firstLoading")){//初次加载
adapter=new ListViewAdapter(MainActivity.this, listDatas);
current=adapter.getCount()+1;
listView.setAdapter(adapter);
listView.loadComplete();
}else if(type.equals("addLoading")){//初次加载后请求的数据，执行notifyDataSetChanged();
adapter.notifyDataSetChanged();
current=adapter.getCount()+1;
listView.loadComplete();
}
} protected void showMsg(String str) {
Toast.makeText(MainActivity.this, "已加载完毕", Toast.LENGTH_SHORT).show();
listView.loadComplete();
} }
模拟服务器端数据
package com.example.listviewdynamicloading; import java.util.ArrayList; public class ListViewDatas {
//模拟服务器端数据库中的数据，假设现在只有3条数据
public static int NUM=53;
public static ArrayList<String> returnNum(int startNum,int endNum){
ArrayList<String> list=new ArrayList<String>();
if(endNum<=NUM){//客户端请求的数据在数据库数据范围之内
for(int i=startNum;i<=endNum;i++){
list.add(String.valueOf(i));
}
return list;
}else if(endNum>=NUM&&startNum<=NUM){//客户端请求的数据不全在数据库数据范围之内
for(int i=startNum;i<=NUM;i++){
list.add(String.valueOf(i));
}
return list;
}else if(startNum>NUM){//客户端请求的数据超出数据库数据范围之内
return null;
}
return null;
}
}
ListView适配器
package com.example.listviewdynamicloading; import java.util.ArrayList; import android.content.Context;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.BaseAdapter;
import android.widget.TextView; public class ListViewAdapter extends BaseAdapter{
private Context context;
private ArrayList<String> datas; public ListViewAdapter(Context context,ArrayList<String> datas){
this.context=context;
this.datas=datas;
} @Override
public int getCount() {
return datas.size();
} @Override
public Object getItem(int position) {
return null;
} @Override
public long getItemId(int position) {
return position;
} @Override
public View getView(int position, View convertView, ViewGroup parent) {
ViewHolder vh=null;
if(convertView==null){
vh=new ViewHolder();
convertView=LayoutInflater.from(context).inflate(R.layout.listview_item, null);
vh.tv=(TextView) convertView.findViewById(R.id.tv);
convertView.setTag(vh);
}else {
vh=(ViewHolder) convertView.getTag();
}
vh.tv.setText("这是第"+datas.get(position)+"条数据");
return convertView;
} class ViewHolder{
TextView tv;
} }
