如何在Android中的ListView中延迟加载图像

如何在Android中的ListView中延迟加载图像

这是我创建的用于保存应用程序当前正在显示的图像的内容。请注意，此处使用的“ Log”对象是我在Android内部最终Log类周围的自定义包装。

package com.wilson.android.library;import java.io.IOException;public class DrawableManager {    private final Map<String, Drawable> drawableMap;    public DrawableManager() {        drawableMap = new HashMap<String, Drawable>();    }    public Drawable fetchDrawable(String urlString) {        if (drawableMap.containsKey(urlString)) { return drawableMap.get(urlString);        }        Log.d(this.getClass().getSimpleName(), "image url:" + urlString);        try { InputStream is = fetch(urlString); Drawable drawable = Drawable.createFromStream(is, "src"); if (drawable != null) {     drawableMap.put(urlString, drawable);     Log.d(this.getClass().getSimpleName(), "got a thumbnail drawable: " + drawable.getBounds() + ", "  + drawable.getIntrinsicHeight() + "," + drawable.getIntrinsicWidth() + ", "  + drawable.getMinimumHeight() + "," + drawable.getMinimumWidth()); } else {   Log.w(this.getClass().getSimpleName(), "could not get thumbnail"); } return drawable;        } catch (MalformedURLException e) { Log.e(this.getClass().getSimpleName(), "fetchDrawable failed", e); return null;        } catch (IOException e) { Log.e(this.getClass().getSimpleName(), "fetchDrawable failed", e); return null;        }    }    public void fetchDrawableonThread(final String urlString, final ImageView imageView) {        if (drawableMap.containsKey(urlString)) { imageView.setImageDrawable(drawableMap.get(urlString));        }        final Handler handler = new Handler() { @Override public void handleMessage(Message message) {     imageView.setImageDrawable((Drawable) message.obj); }        };        Thread thread = new Thread() { @Override public void run() {     //TODO : set imageView to a "pending" image     Drawable drawable = fetchDrawable(urlString);     Message message = handler.obtainMessage(1, drawable);     handler.sendMessage(message); }        };        thread.start();    }    private InputStream fetch(String urlString) throws MalformedURLException, IOException {        DefaultHttpClient httpClient = new DefaultHttpClient();        HttpGet request = new HttpGet(urlString);        HttpResponse response = httpClient.execute(request);        return response.getEntity().getContent();    }}