Android实现异步加载
16lz
2021-01-26
效果图
代码
public class ImageLoader { private InputStream inputStream; private HttpURLConnection conn; private ImageView mImageview; private LruCache mLrucache; private ListView mlistview; private String threadUrl; private Set tasks; private Handler mHandler = new Handler(){ @Override public void handleMessage(Message msg) { super.handleMessage(msg); if(mImageview.getTag().equals(threadUrl)){ mImageview.setImageBitmap((Bitmap) msg.obj); } } }; public ImageLoader(ListView listView){ mlistview = listView; tasks = new HashSet<>(); int maxMemory = (int) Runtime.getRuntime().maxMemory(); int cacheSize = maxMemory/8; mLrucache = new LruCache(cacheSize){ @Override protected int sizeOf(String key, Bitmap bitmap) { return bitmap.getByteCount(); } }; } public void addBitmapToCache(String url,Bitmap bitmap){ if(getBitmapFromCache(url)==null){ mLrucache.put(url,bitmap); } } public Bitmap getBitmapFromCache(String mUrl){ return mLrucache.get(mUrl); } public void showImageByThread(ImageView imageView, final String url){ mImageview = imageView; threadUrl = url; new Thread(){ @Override public void run() { super.run(); Bitmap bitmap = getBitmapFromUrl(url); Message message = Message.obtain(); message.obj = bitmap; mHandler.sendMessage(message); } }.start(); } public Bitmap getBitmapFromUrl(String urlString){ Bitmap bitmap = null; try { URL url = new URL(urlString); conn = (HttpURLConnection) url.openConnection(); conn.setConnectTimeout(2000); conn.setReadTimeout(2000); if(conn.getResponseCode()==200){ inputStream = new BufferedInputStream(conn.getInputStream()); bitmap = BitmapFactory.decodeStream(inputStream); return bitmap; } } catch (MalformedURLException e) { e.printStackTrace(); } catch (IOException e) { e.printStackTrace(); }finally { conn.disconnect(); try { inputStream.close(); } catch (IOException e) { e.printStackTrace(); } } return null; } public void showImageByAsyncTask(ImageView imageView,String url){ Bitmap bitmap = getBitmapFromCache(url); if(bitmap != null){ imageView.setImageBitmap(bitmap); }else{ //getView的时候不去下载// new NewsTask(url).execute(url); imageView.setImageResource(R.mipmap.ic_launcher); } } private class NewsTask extends AsyncTask{ private String mUrl; public NewsTask(String url){ mUrl = url; } @Override protected Bitmap doInBackground(String... params) { String url = params[0]; Bitmap bitmap = getBitmapFromUrl(url); if(bitmap!=null){ addBitmapToCache(url,bitmap); } return bitmap; } @Override protected void onPostExecute(Bitmap bitmap) { super.onPostExecute(bitmap);// if(mImageview.getTag().equals(mUrl)){// mImageview.setImageBitmap(bitmap);// } ImageView imageView = (ImageView) mlistview.findViewWithTag(mUrl); if(imageView!=null&&bitmap!=null){ imageView.setImageBitmap(bitmap); } tasks.remove(this); } } public void loadImages(int start,int end){ for (int i = start; i < end; i++) { String url = NewsAdapter.URLS[i]; Bitmap bitmap = getBitmapFromCache(url); if(bitmap != null){ ImageView imageView = (ImageView) mlistview.findViewWithTag(url); imageView.setImageBitmap(bitmap); }else{ NewsTask task = new NewsTask(url); task.execute(url); tasks.add(task); } } } public void canCellAllTask(){ for (NewsTask task:tasks) { task.cancel(false); } }} public class NewsAdapter extends BaseAdapter implements AbsListView.OnScrollListener{ private Context context; private List listDataBeen; private LayoutInflater mInflate; private String url; private ImageLoader mImageLoader; private int mStart; private int mEnd; public static String[] URLS; private ListView mListview; private boolean isFirstShow = true; public NewsAdapter(Context context, List dataBeen,ListView listView){ this.context = context; this.listDataBeen = dataBeen; mInflate = LayoutInflater.from(context); mListview = listView; mImageLoader = new ImageLoader(mListview); URLS = new String[dataBeen.size()]; for(int i = 0;i< dataBeen.size();i++){ URLS[i] = dataBeen.get(i).picBig; } listView.setOnScrollListener(this); } @Override public int getCount() { return listDataBeen.size(); } @Override public MewsBean.DataBean getItem(int position) { return listDataBeen.get(position); } @Override public long getItemId(int position) { return position; } @Override public View getView(int position, View convertView, ViewGroup parent) { ViewHodler hodler; if(convertView == null){ convertView = mInflate.inflate(R.layout.item_layout,null); hodler = new ViewHodler(); hodler.imageView = (ImageView) convertView.findViewById(R.id.iv_icon); hodler.tvTitle = (TextView) convertView.findViewById(R.id.tv_title); hodler.tvContent = (TextView) convertView.findViewById(R.id.tv_content); convertView.setTag(hodler); }else{ hodler = (ViewHodler) convertView.getTag(); } MewsBean.DataBean dataBean = listDataBeen.get(position); hodler.imageView.setImageResource(R.mipmap.ic_launcher); url = dataBean.picBig; hodler.imageView.setTag(url);// new ImageLoader().showImageByThread(hodler.imageView,url);// new ImageLoader().showImageByAsyncTask(hodler.imageView,url);// mImageLoader.showImageByAsyncTask(hodler.imageView,url); hodler.tvTitle.setText(dataBean.name); hodler.tvContent.setText(dataBean.description); return convertView; } @Override public void onScrollStateChanged(AbsListView view, int scrollState) { if(scrollState == SCROLL_STATE_IDLE){ mImageLoader.loadImages(mStart,mEnd); }else{ //停止所有加载 mImageLoader.canCellAllTask(); } } //第一次进来的时候此方法会调用 @Override public void onScroll(AbsListView view, int firstVisibleItem, int visibleItemCount, int totalItemCount) { mStart = firstVisibleItem; mEnd = firstVisibleItem + visibleItemCount; //初始化调用的时候visibleItemCount=0,此时item还没有加载 if(isFirstShow&&visibleItemCount>0){ mImageLoader.loadImages(mStart,mEnd); isFirstShow = false; } } public static class ViewHodler{ public ImageView imageView; public TextView tvTitle; public TextView tvContent; }} public class MainActivity extends Activity{ ListView listview; private ListAdapter adapter; //这里必须带http的前缀 public static final String URL = "http://www.imooc.com/api/teacher?type=4&num=30"; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); listview = (ListView) findViewById(R.id.listview); new NewsTask().execute(URL); } class NewsTask extends AsyncTask>{ @Override protected List doInBackground(String... params) { return getJsonData(params[0]); } @Override protected void onPostExecute(List dataBeen) { super.onPostExecute(dataBeen); NewsAdapter adapter = new NewsAdapter(MainActivity.this,dataBeen,listview); listview.setAdapter(adapter); } } public List getJsonData(String url){ List list = new ArrayList<>(); try { //此句功能与url.openConnection().openInputStream功能相同 String jsonString = getJsonString(new URL(url).openStream()); Gson gson = new Gson(); MewsBean mewsBean = gson.fromJson(jsonString, MewsBean.class); for (int i = 0; i < mewsBean.data.size(); i++) { list.add(mewsBean.data.get(i)); } } catch (IOException e) { e.printStackTrace(); } return list; } public String getJsonString(InputStream inputStream){ String result = ""; InputStreamReader isr = null; try { String line = ""; isr = new InputStreamReader(inputStream,"utf-8"); BufferedReader reader = new BufferedReader(isr); while((line = reader.readLine())!=null){ result+=line; } } catch (UnsupportedEncodingException e) { e.printStackTrace(); } catch (IOException e) { e.printStackTrace(); 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