android中listview分頁載入資料
阿新 • • 發佈:2019-01-10
前段時間做的新浪微博專案一直想實現listview分頁載入資料,今天終於實現了,哈哈!感覺挺好的,今天又寫了個demo給大家分享下。
首先說下listview的優化方案,這也是面試中常考的題目。優化方案有三種:1,如果自定義介面卡,那麼在getView方法中判斷contentView是否為空,如果為空建立contentView並返回,如果不為空直接返回contentView。這樣能儘可能少建立view。2.給contentView設定tag,傳入一個viewHoder物件,用於快取要實現的資料。3,如果listview中顯示的item太多,就要考慮分頁載入了。
下面就注意介紹一下分頁載入資料。首先在layout下建立listview.xml:
然後建立listview_item.xml:<?xml version="1.0" encoding="utf-8"?> <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" android:layout_width="match_parent" android:layout_height="match_parent" android:orientation="vertical" > <ListView android:id="@+id/listView1" android:layout_width="match_parent" android:layout_height="wrap_content" > </ListView> </LinearLayout>
<?xml version="1.0" encoding="utf-8"?> <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" android:orientation="vertical" android:layout_width="fill_parent" android:layout_height="fill_parent"> <TextView android:id="@+id/list_item_text" android:layout_width="fill_parent" android:layout_height="fill_parent" android:gravity="center" android:textSize="20sp" android:paddingTop="10dp" android:paddingBottom="10dp"/> </LinearLayout>
再為跟多按鈕新增一個xml:
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:gravity="center"
android:orientation="vertical" >
<Button
android:id="@+id/loadMoreButton"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:onClick="loadMore"
android:text="載入更多" />
</LinearLayout>
程式碼部分:
public class ListViewAdapter extends BaseAdapter {
private static Map<Integer,View> m=new HashMap<Integer,View>();
private List<String> items;
private LayoutInflater inflater;
public ListViewAdapter(List<String> items, Context context) {
super();
this.items = items;
this.inflater = (LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
}
@Override
public int getCount() {
// TODO Auto-generated method stub
return items.size();
}
@Override
public Object getItem(int position) {
// TODO Auto-generated method stub
return items.get(position);
}
@Override
public long getItemId(int position) {
// TODO Auto-generated method stub
return position;
}
@Override
public View getView(int position, View contentView, ViewGroup arg2) {
// TODO Auto-generated method stub
contentView=m.get(position);
if(contentView==null){
contentView=inflater.inflate(R.layout.listview_item, null);
TextView text=(TextView) contentView.findViewById(R.id.list_item_text);
text.setText(items.get(position));
}
m.put(position, contentView);
return contentView;
}
public void addItem(String item) {
items.add(item);
}
}
public class ListViewActivity extends Activity implements OnScrollListener {
List<String> items = new ArrayList<String>();
private ListView listView;
private int visibleLastIndex = 0; //最後的可視項索引
private int visibleItemCount; // 當前視窗可見項總數
private ListViewAdapter adapter;
private View loadMoreView;
private Button loadMoreButton;
private Handler handler = new Handler();
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.listview);
loadMoreView = getLayoutInflater().inflate(R.layout.load_more, null);
loadMoreButton = (Button) loadMoreView.findViewById(R.id.loadMoreButton);
loadMoreButton.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View v) {
// TODO Auto-generated method stub
loadMoreButton.setText("正在載入..."); //設定按鈕文字loading
handler.postDelayed(new Runnable() {
@Override
public void run() {
loadData();
adapter.notifyDataSetChanged(); //資料集變化後,通知adapter
listView.setSelection(visibleLastIndex - visibleItemCount + 1); //設定選中項
loadMoreButton.setText("載入更多"); //恢復按鈕文字
}
}, 1000);
}
});
listView = (ListView) this.findViewById(R.id.listView1);
listView.addFooterView(loadMoreView); //設定列表底部檢視
// listView.addHeaderView(v) //設定列表頂部檢視
initAdapter();
listView.setAdapter(adapter); //自動為id是list的ListView設定介面卡
listView.setOnScrollListener(this); //新增滑動監聽
listView.setOnItemClickListener(new OnItemClickListener() {
@Override
public void onItemClick(AdapterView<?> arg0, View view,
int position, long arg3) {
// TODO Auto-generated method stub
Toast.makeText(getApplicationContext(), items.get(position),Toast.LENGTH_SHORT).show();
}
});
}
/**
* 初始化介面卡
*/
private void initAdapter() {
for (int i = 0; i < 20; i++) {
items.add(String.valueOf(i + 1));
}
adapter = new ListViewAdapter(items,this);
}
/**
* 滑動時被呼叫
*/
@Override
public void onScroll(AbsListView view, int firstVisibleItem, int visibleItemCount, int totalItemCount) {
this.visibleItemCount = visibleItemCount;
visibleLastIndex = firstVisibleItem + visibleItemCount - 1;
}
/**
* 滑動狀態改變時被呼叫
*/
@Override
public void onScrollStateChanged(AbsListView view, int scrollState) {
int itemsLastIndex = adapter.getCount() - 1; //資料集最後一項的索引
int lastIndex = itemsLastIndex + 1; //加上底部的loadMoreView項
if (scrollState == OnScrollListener.SCROLL_STATE_IDLE && visibleLastIndex == lastIndex) {
//如果是自動載入,可以在這裡放置非同步載入資料的程式碼
Log.i("LOADMORE", "loading...");
}
}
/**
* 模擬載入資料
*/
private void loadData() {
int count = adapter.getCount();
for (int i = count; i < count + 20; i++) {
adapter.addItem(String.valueOf(i + 1));
}
}
}
最後看看效果: