大家好,又见面了,我是全栈君,今天给大家准备了Idea注册码。
前段时间做的新浪微博项目一直想实现listview分页载入数据,今天最终实现了,哈哈!感觉挺好的,今天又写了个demo给大家分享下。
首先说下listview的优化方案,这也是面试中常考的题目。优化方案有三种:1,假设自己定义适配器,那么在getView方法中推断contentView是否为空,假设为空创建contentView并返回,假设不为空直接返回contentView。这样能尽可能少创建view。2.给contentView设置tag,传入一个viewHoder对象,用于缓存要实现的数据。3,假设listview中显示的item太多,就要考虑分页载入了。
以下就注意介绍一下分页载入数据。首先在layout下创建listview.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>
然后创建listview_item.xml:
<?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>
再为跟多button加入一个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="载入很多其它" /> </LinearLayout>
代码部分:
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; //最后的可视项索引 private int visibleItemCount; // 当前窗体可见项总数 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("正在载入..."); //设置button文字loading handler.postDelayed(new Runnable() { @Override public void run() { loadData(); adapter.notifyDataSetChanged(); //数据集变化后,通知adapter listView.setSelection(visibleLastIndex - visibleItemCount + 1); //设置选中项 loadMoreButton.setText("载入很多其它"); //恢复button文字 } }, 1000); } }); listView = (ListView) this.findViewById(R.id.listView1); listView.addFooterView(loadMoreView); //设置列表底部视图 // listView.addHeaderView(v) //设置列表顶部视图 initAdapter(); listView.setAdapter(adapter); //自己主动为id是list的ListView设置适配器 listView.setOnScrollListener(this); //加入滑动监听 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(); } }); } /** * 初始化适配器 */ private void initAdapter() { for (int i = 0; i < 20; i++) { items.add(String.valueOf(i + 1)); } adapter = new ListViewAdapter(items,this); } /** * 滑动时被调用 */ @Override public void onScroll(AbsListView view, int firstVisibleItem, int visibleItemCount, int totalItemCount) { this.visibleItemCount = visibleItemCount; visibleLastIndex = firstVisibleItem + visibleItemCount - 1; } /** * 滑动状态改变时被调用 */ @Override public void onScrollStateChanged(AbsListView view, int scrollState) { int itemsLastIndex = adapter.getCount() - 1; //数据集最后一项的索引 int lastIndex = itemsLastIndex + 1; //加上底部的loadMoreView项 if (scrollState == OnScrollListener.SCROLL_STATE_IDLE && visibleLastIndex == lastIndex) { //假设是自己主动载入,能够在这里放置异步载入数据的代码 Log.i("LOADMORE", "loading..."); } } /** * 模拟载入数据 */ private void loadData() { int count = adapter.getCount(); for (int i = count; i < count + 20; i++) { adapter.addItem(String.valueOf(i + 1)); } } }
最后看看效果:
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