Android中ListView動態加載數據

1. 引言：

 

為了提高ListView的效率和應用程序的性能，在Android應用程序中不應該一次性加載ListView所要顯示的全部信息，而是采取分批加載策略，隨着用戶的滑動，動態的從后台加載所需的數據，並渲染到ListView組件中，這樣可以極大的改善應用程序的性能和用戶體驗。

2. 交互：

 

進入ListView組件，首先預加載N條記錄，當用戶滑動到最后一條記錄顯示加載提示信息，並從后台加載N條數據，接着渲染UI界面。

3. 效果圖：

 

4. 程序實現：

package com.focus.loading;
import android.app.ListActivity;
import android.os.Bundle;
import android.os.Handler;
import android.view.Gravity;
import android.view.View;
import android.view.ViewGroup;
import android.widget.AbsListView;
import android.widget.BaseAdapter;
import android.widget.LinearLayout;
import android.widget.ListView;
import android.widget.ProgressBar;
import android.widget.TextView;
import android.widget.AbsListView.OnScrollListener;
import android.widget.LinearLayout.LayoutParams;
public class ListViewLoadingActivity extends ListActivity implements
        OnScrollListener {
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        /**
         * "加載項"布局，此布局被添加到ListView的Footer中。
         */
        mLoadLayout = new LinearLayout(this);
        mLoadLayout.setMinimumHeight(60);
        mLoadLayout.setGravity(Gravity.CENTER);
        mLoadLayout.setOrientation(LinearLayout.HORIZONTAL);
        /**
         * 向"加載項"布局中添加一個圓型進度條。
         */
        ProgressBar mProgressBar = new ProgressBar(this);
        mProgressBar.setPadding(0, 0, 15, 0);
        mLoadLayout.addView(mProgressBar, mProgressBarLayoutParams);
        /**
         * 向"加載項"布局中添加提示信息。
         */
        TextView mTipContent = new TextView(this);
        mTipContent.setText("加載中...");
        mLoadLayout.addView(mTipContent, mTipContentLayoutParams);
        /**
         * 獲取ListView組件，並將"加載項"布局添加到ListView組件的Footer中。
         */
        mListView = getListView();
        mListView.addFooterView(mLoadLayout);
        /**
         * 組ListView組件設置Adapter,並設置滑動監聽事件。
         */
        setListAdapter(mListViewAdapter);
        mListView.setOnScrollListener(this);
    }
    public void onScroll(AbsListView view, int mFirstVisibleItem,
            int mVisibleItemCount, int mTotalItemCount) {
        mLastItem = mFirstVisibleItem + mVisibleItemCount - 1;
        if (mListViewAdapter.count > mCount) {
            mListView.removeFooterView(mLoadLayout);
        }
    }
    public void onScrollStateChanged(AbsListView view, int mScrollState) {

        /**
         * 當ListView滑動到最后一條記錄時這時，我們會看到已經被添加到ListView的"加載項"布局， 這時應該加載剩余數據。
         */
        if (mLastItem == mListViewAdapter.count
                && mScrollState == OnScrollListener.SCROLL_STATE_IDLE) {
            if (mListViewAdapter.count <= mCount) {
                mHandler.postDelayed(new Runnable() {
                    @Override
                    public void run() {
                        mListViewAdapter.count += 10;
                        mListViewAdapter.notifyDataSetChanged();
                        mListView.setSelection(mLastItem);
                    }
                }, 1000);
            }
        }
    }
    class ListViewAdapter extends BaseAdapter {
        int count = 10;
        public int getCount() {
            return count;
        }
        public Object getItem(int position) {
            return position;
        }
        public long getItemId(int position) {
            return position;
        }
        public View getView(int position, View view, ViewGroup parent) {
            TextView mTextView;
            if (view == null) {
                mTextView = new TextView(ListViewLoadingActivity.this);
            } else {
                mTextView = (TextView) view;
            }
            mTextView.setText("Item " + position);
            mTextView.setTextSize(20f);
            mTextView.setGravity(Gravity.CENTER);
            mTextView.setHeight(60);
            return mTextView;
        }
    }
    private LinearLayout mLoadLayout;
    private ListView mListView;
    private ListViewAdapter mListViewAdapter = new ListViewAdapter();
    private int mLastItem = 0;
    private int mCount = 41;
    private final Handler mHandler = new Handler();
    private final LayoutParams mProgressBarLayoutParams = new LinearLayout.LayoutParams(
            LinearLayout.LayoutParams.WRAP_CONTENT,
            LinearLayout.LayoutParams.WRAP_CONTENT);
    private final LayoutParams mTipContentLayoutParams = new LinearLayout.LayoutParams(
            LinearLayout.LayoutParams.WRAP_CONTENT,
            LinearLayout.LayoutParams.WRAP_CONTENT);
}