我正在构建一个包含大量1000张图片的图片的网格视图。为了减少gridview的加载时间，我想使用AbsListView实现onScrollListener。我将限制每个视图20个图像，然后当滚动到达底部时，它将加载另外20个图像。这将重复，直到所有图像都已加载。
我一直在谷歌搜索样本，但似乎找不到适合我的代码。谁能指导我怎么做？我目前正在使用图像加载器Lazylist作为我的图像。我也在使用AsyncTask。
MainGridView.class
public class MainGridView extends SherlockActivity {
private ProgressDialog pDialog;
ArrayList<HashMap<String, String>> songsList;
static final String KEY_SONG = "song";
static final String KEY_ID = "id";
static final String KEY_TITLE = "title";
static final String KEY_ARTIST = "artist";
static final String KEY_CAT_ARTIST = "artistcat";
static final String KEY_DURATION = "duration";
static final String KEY_THUMB_URL = "thumb_url";
static final String KEY_BIG_URL = "big_url";
static final String KEY_CAT_URL = "cat_url";
static String IMAGE_POSITION;
GridView grid;
MainGridViewLazyAdapter adapter;
String cat_url;
String artist_url;
private int visibleThreshold = 5;
private int currentPage = 0;
private int previousTotal = 0;
private boolean loading = true;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.gridview_main);
getSupportActionBar().setDisplayHomeAsUpEnabled(true);
checkInternetConnection();
grid = (GridView) findViewById(R.id.grid_view);
grid.setOnScrollListener(new OnScrollListener() {
@Override
public void onScroll(AbsListView view, int firstVisibleItem,
int visibleItemCount, int totalItemCount) {
// TODO Auto-generated method stub
if (loading) {
if (visibleItemCount > totalItemCount) {
loading = false;
previousTotal = totalItemCount;
currentPage++;
}
}
if (!loading && (totalItemCount - visibleItemCount) <= (firstVisibleItem + visibleThreshold)) {
// I load the next page of gigs using a background task,
// but you can call any function here.
new loadGridView().execute(currentPage + 1);
loading = true;
}
}
@Override
public void onScrollStateChanged(AbsListView view, int scrollState) {
// TODO Auto-generated method stub
}
});
}
public class loadGridView extends AsyncTask<Integer, String, String> {
@Override
protected void onPreExecute() {
super.onPreExecute();
pDialog = new ProgressDialog(MainGridView.this);
pDialog.setTitle("Connect to Server");
pDialog.setMessage("This process can take a few seconds to a few minutes, depending on your Internet Connection Speed.");
pDialog.setIndeterminate(false);
pDialog.setCancelable(false);
pDialog.show();
}
@Override
protected String doInBackground(Integer... args) {
// updating UI from Background Thread
Intent in = getIntent();
songsList = new ArrayList<HashMap<String, String>>();
cat_url = in.getStringExtra(KEY_CAT_URL);
artist_url = in.getStringExtra(KEY_CAT_ARTIST);
XMLParser parser = new XMLParser();
String xml = parser.getXmlFromUrl(cat_url); // getting XML from URL
Document doc = parser.getDomElement(xml); // getting DOM element
NodeList nl = doc.getElementsByTagName(KEY_SONG);
// looping through all song nodes <song>
for (int i = 0; i < nl.getLength(); i++) {
// creating new HashMap
HashMap<String, String> map = new HashMap<String, String>();
Element e = (Element) nl.item(i);
// adding each child node to HashMap key => value
map.put(KEY_ID, parser.getValue(e, KEY_ID));
map.put(KEY_TITLE, parser.getValue(e, KEY_TITLE));
map.put(KEY_ARTIST, parser.getValue(e, KEY_ARTIST));
map.put(KEY_DURATION, parser.getValue(e, KEY_DURATION));
map.put(KEY_THUMB_URL, parser.getValue(e, KEY_THUMB_URL));
map.put(KEY_BIG_URL, parser.getValue(e, KEY_BIG_URL));
// adding HashList to ArrayList
songsList.add(map);
}
return null;
}
@Override
protected void onPostExecute(String args) {
ActionBar ab = getSupportActionBar();
ab.setTitle(artist_url);
adapter=new MainGridViewLazyAdapter(MainGridView.this, songsList);
grid.setAdapter(adapter);
pDialog.dismiss();
}
}
答案 0 :(得分：5)
我想你想从Urls加载图片。为此，您可以使用此解决方案：Lazy load of images in ListView
为了使用onScrollListener控制您的分页，我想您希望看到Endless scrolling example。这是一个简单的示例，但您必须添加的唯一内容是检查是否已到达xml的最后一项。
在AsyncTask（在每次新加载时调用）中，您只需解析xml中的一些数据（对应于您的情况下的20个项目）。这是基于您的代码的使用示例：
public class MainGridView extends SherlockActivity implements OnScrollListener {
public static final String KEY_SONG = "song";
public static final String KEY_ID = "id";
public static final String KEY_TITLE = "title";
public static final String KEY_ARTIST = "artist";
public static final String KEY_CAT_ARTIST = "artistcat";
public static final String KEY_DURATION = "duration";
public static final String KEY_THUMB_URL = "thumb_url";
public static final String KEY_BIG_URL = "big_url";
public static final String KEY_CAT_URL = "cat_url";
private final static int ITEMS_PPAGE = 20;
private ProgressDialog mDialog;
private ArrayList<HashMap<String, String>> mSongsList;
private static String IMAGE_POSITION;
private GridView mGridView;
//MainGridViewLazyAdapter mAdapter;
private ArrayAdapter<String> mAdapter;
private String cat_url;
private String artist_url;
private int mVisibleThreshold = 5;
private int mCurrentPage = 0;
private int mPreviousTotal = 0;
private boolean mLoading = true;
private boolean mLastPage = false;
private String mXml;
@Override
public void onCreate(Bundle savedInstanceState) {
setTheme(SherlockBarUtils.getCurrentTheme(this));
super.onCreate(savedInstanceState);
setContentView(R.layout.gridview_main);
getSupportActionBar().setDisplayHomeAsUpEnabled(true);
//checkInternetConnection();
mGridView = (GridView) findViewById(R.id.grid_view);
mGridView.setOnScrollListener(this);
mAdapter = new ArrayAdapter<String>(this, android.R.layout.simple_list_item_1);
//mAdapter=new MainGridViewLazyAdapter(MainGridView.this);
mGridView.setAdapter(mAdapter);
new DownloadDataAsyncTask().execute();
}
@Override
public void onScroll(AbsListView view, int firstVisibleItem, int visibleItemCount, int totalItemCount) {
if (mLoading) {
if (totalItemCount > mPreviousTotal) {
mLoading = false;
mPreviousTotal = totalItemCount;
mCurrentPage++;
// Find your own condition in order to know when you
// have finished displaying all items
if (mCurrentPage + 1 > 50) {
mLastPage = true;
}
}
}
if (!mLastPage && !mLoading &&
(totalItemCount - visibleItemCount) <= (firstVisibleItem + mVisibleThreshold)) {
new AddItemsAsyncTask().execute();
mLoading = true;
}
}
@Override
public void onScrollStateChanged(AbsListView view, int scrollState) {
}
public class DownloadDataAsyncTask extends AsyncTask<String, String, String> {
@Override
protected void onPreExecute() {
super.onPreExecute();
mDialog = new ProgressDialog(MainGridView.this);
mDialog.setTitle("Connect to Server");
mDialog.setMessage("This process can take a few seconds to a few minutes, depending on your Internet Connection Speed.");
mDialog.setIndeterminate(false);
mDialog.setCancelable(false);
mDialog.show();
}
@Override
protected String doInBackground(String... args) {
// Downloading XML
/*
Intent in = getIntent();
mSongsList = new ArrayList<HashMap<String, String>>();
cat_url = in.getStringExtra(KEY_CAT_URL);
artist_url = in.getStringExtra(KEY_CAT_ARTIST);
XMLParser parser = new XMLParser();
mXml = parser.getXmlFromUrl(cat_url); // getting XML from URL
*/
return null;
}
@Override
protected void onPostExecute(String args) {
/*
getSupportActionBar().setTitle(artist_url);
*/
mDialog.dismiss();
mLoading = false;
}
}
public class AddItemsAsyncTask extends AsyncTask<Integer, String, String> {
@Override
protected void onPreExecute() {
super.onPreExecute();
}
@Override
protected String doInBackground(Integer... args) {
MainGridView.this.runOnUiThread(new Runnable() {
@Override
public void run() {
// Parsing 20 more items and adding them to the adapter
for (int i = mCurrentPage * ITEMS_PPAGE; i < (mCurrentPage + 1) * ITEMS_PPAGE; i++) {
MainGridView.this.mAdapter.add(String.valueOf(Math.random() * 5000));
}
MainGridView.this.mAdapter.notifyDataSetChanged();
}
});
return null;
}
@Override
protected void onPostExecute(String args) {
}
}
}
为方便起见，我在GridView内使用了文本而不是图像。我专注于分页系统所以我没有解析XML，只是动态添加了一些随机值。
此外，您可以考虑使用相同的addItemsAsyncTask在每次加载时仅下载xml的一部分（20个项目），而不是在创建GridView之前下载整个1000多个项目。