泊之心
2017-01-17 15:29:22浏览 2915
1.MainActivity
public class MainActivity extends Activity {
private ListView listView;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
listView = (ListView) findViewById(R.id.listView);
String url = "http://www.imooc.com/api/teacher?type=4&num=30";
new mAsyncTask().execute(url);
}
private List<ItemBean> getJsonData(String url){
List<ItemBean> jsonList = new ArrayList<ItemBean>();
try {
InputStream is = new URL(url).openStream();
String jsonString = readStream(is);
JSONObject object = new JSONObject(jsonString);
JSONArray arr = object.getJSONArray("data");
ItemBean mItemBean;
for(int i=0;i<arr.length();i++){
JSONObject object2 = arr.getJSONObject(i);
mItemBean = new ItemBean();
mItemBean.imageUrl = object2.getString("picSmall");
mItemBean.title = object2.getString("name");
mItemBean.content = object2.getString("description");
jsonList.add(mItemBean);
}
return jsonList;
} catch (MalformedURLException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (JSONException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
return null;
}
private String readStream(InputStream is){
try {
InputStreamReader isr = new InputStreamReader(is,"gbk");
BufferedReader br = new BufferedReader(isr);
StringBuffer sb = new StringBuffer();
String str;
while((str=br.readLine())!=null){
sb.append(str);
}
isr.close();
br.close();
is.close();
return sb.toString();
} catch (UnsupportedEncodingException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
return null;
}
public class mAsyncTask extends AsyncTask<String, Void, List<ItemBean>>{
@Override
protected List<ItemBean> doInBackground(String... params) {
return getJsonData(params[0]);
}
@Override
protected void onPostExecute(List<ItemBean> result) {
ListView_Adapter mAdapter = new ListView_Adapter(result,MainActivity.this,listView);
listView.setAdapter(mAdapter);
super.onPostExecute(result);
}
}
}
2.ItemBean
public class ItemBean {
public String imageUrl;
public String title;
public String content;
}
3.ListView_Adapter
public class ListView_Adapter extends BaseAdapter implements OnScrollListener{
private List<ItemBean> itemList;
private LayoutInflater inflator;
private ImageLoader imageLoader;
public static String[] URLS;
private int mStart,mEnd;
private boolean firstInTag = true;
public ListView_Adapter(List<ItemBean> itemList,Context context,ListView listView) {
this.itemList = itemList;
inflator = LayoutInflater.from(context);
imageLoader = new ImageLoader(listView);
URLS = new String[itemList.size()];
for(int i=0;i<itemList.size();i++){
URLS[i] = itemList.get(i).imageUrl;
}
listView.setOnScrollListener(this);
}
@Override
public int getCount() {
return itemList.size();
}
@Override
public Object getItem(int position) {
// TODO Auto-generated method stub
return itemList.get(position);
}
@Override
public long getItemId(int position) {
// TODO Auto-generated method stub
return position;
}
@Override
public View getView(int position, View convertView, ViewGroup parent) {
ViewHolder holder;
if(convertView==null){
holder = new ViewHolder();
convertView = inflator.inflate(R.layout.item_layout, null);
holder.imageView = (ImageView) convertView.findViewById(R.id.imageView);
holder.content = (TextView) convertView.findViewById(R.id.text_content);
holder.title = (TextView) convertView.findViewById(R.id.text_title);
convertView.setTag(holder);
}else{
holder = (ViewHolder) convertView.getTag();
}
holder.imageView.setImageResource(R.drawable.ic_launcher);
holder.imageView.setTag(itemList.get(position).imageUrl);
//new ImageLoader().showImageByThread(holder.imageView, itemList.get(position).imageUrl);
//imageLoader.showImageByAsyncTask(holder.imageView, itemList.get(position).imageUrl);
holder.title.setText(itemList.get(position).title);
holder.content.setText(itemList.get(position).content);
return convertView;
}
class ViewHolder{
private ImageView imageView;
private TextView title;
private TextView content;
}
@Override
public void onScroll(AbsListView view, int firstVisibleItem,
int visibleItemCount, int totalItemCount) {
mStart = firstVisibleItem;
mEnd = firstVisibleItem+visibleItemCount;
if(firstInTag&&visibleItemCount>0){
imageLoader.loadImage(mStart, mEnd);
firstInTag = false;
}
}
@Override
public void onScrollStateChanged(AbsListView view, int scrollState) {
if(scrollState==SCROLL_STATE_IDLE){ //没有滚动
imageLoader.loadImage(mStart, mEnd);
}else{ //滚动中
imageLoader.cancelAllTasks();
}
}
}
4.ImageLoader
public class ImageLoader {
private LruCache<String, Bitmap> mCache;
private ListView mListView;
private Set<LoadImageTask> mTasks;
public ImageLoader(ListView listView){
mListView = listView;
mTasks = new HashSet<ImageLoader.LoadImageTask>();
//获取最大可用内存
int maxMemory = (int) Runtime.getRuntime().maxMemory();
int cacheSize = maxMemory/4;
mCache = new LruCache<String, Bitmap>(cacheSize){
@Override
protected int sizeOf(String key, Bitmap value) {
//返回图片大小，每次存入缓存时调用
return value.getByteCount();
};
};
}
public void addBitmapToCache(String url,Bitmap bm){
mCache.put(url,bm);
if(getBitmapFromCache(url)!=null){
System.out.println("添加");
}
}
public Bitmap getBitmapFromCache(String url){
return mCache.get(url);
}
public void showImageByThread(ImageView imageView, String url){
final String imageUrl = url;
final ImageView mImageView = imageView;
final Handler mHandler = new Handler(){
public void handleMessage(android.os.Message msg) {
if(mImageView.getTag().equals(imageUrl)){
mImageView.setImageBitmap((Bitmap) msg.obj);
}
};
};
new Thread(){
@Override
public void run() {
Bitmap bm = getBitmapFromUrl(imageUrl);
Message message = new Message();
message.obj = bm;
mHandler.sendMessage(message);
super.run();
}
}.start();
}
public void showImageByAsyncTask(ImageView imageView, String url){
Bitmap bm = getBitmapFromCache(url);
if(bm==null){
System.out.println(1);
//new LoadImageTask(imageView,url).execute(url);
}else{
imageView.setImageBitmap(bm);
}
}
public void loadImage(int start, int end){
for(int i=start;i<end;i++){
String url = ListView_Adapter.URLS[i];
Bitmap bm = getBitmapFromCache(url);
if(bm==null){
LoadImageTask loadImageTask = new LoadImageTask(url);
loadImageTask.execute(url);
mTasks.add(loadImageTask);
}else{
ImageView imageView = (ImageView) mListView.findViewWithTag(url);
imageView.setImageBitmap(bm);
}
}
}
public void cancelAllTasks(){
if(mTasks!=null){
for(LoadImageTask loadImageTask:mTasks){
loadImageTask.cancel(true);
}
}
}
private class LoadImageTask extends AsyncTask<String, Void, Bitmap>{
private String url;
public LoadImageTask(String url) {
super();
this.url = url;
}
@Override
protected Bitmap doInBackground(String... params) {
Bitmap bm = getBitmapFromUrl(params[0]);
if(bm!=null){
addBitmapToCache(params[0], bm);
}
return bm;
}
@Override
protected void onPostExecute(Bitmap result) {
super.onPostExecute(result);
ImageView mImageView = (ImageView) mListView.findViewWithTag(url);
if(mImageView!=null&&result!=null){
mImageView.setImageBitmap(result);
}
mTasks.remove(this);
}
}
public Bitmap getBitmapFromUrl(String url){
try {
InputStream is = new URL(url).openConnection().getInputStream();
Bitmap bm = BitmapFactory.decodeStream(is);
is.close();
return bm;
} catch (MalformedURLException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
return null;
}
}