将 json url 中的图像转换为列表视图

Question

我有一个将自定义对象添加到列表视图中的教程from here...现在我想知道如何在同一过程中显示图像和文本...

Answer 1

您可以在您的项目中添加这个 ImageThreadLoader.java：

import java.io.BufferedInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.lang.Thread.State;
import java.lang.ref.SoftReference;
import java.net.MalformedURLException;
import java.net.URL;
import java.net.URLConnection;
import java.util.ArrayList;
import java.util.HashMap;

import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.os.Handler;
import android.util.Log;

/**
 * This is an object that can load images from a URL on a thread.
 *
 * @author Jeremy Wadsack
 */
public class ImageThreadLoader {
    private static final String TAG = "ImageThreadLoader";

    // Global cache of images.
    // Using SoftReference to allow garbage collector to clean cache if needed
    private final HashMap<String, SoftReference<Bitmap>> Cache = new HashMap<String,  SoftReference<Bitmap>>();

    private final class QueueItem {
        public URL url;
        public ImageLoadedListener listener;
    }
    private final ArrayList<QueueItem> Queue = new ArrayList<QueueItem>();

    private final Handler handler = new Handler();  // Assumes that this is started from the main (UI) thread
    private Thread thread;
    private QueueRunner runner = new QueueRunner();;

    /** Creates a new instance of the ImageThreadLoader */
    public ImageThreadLoader() {
        thread = new Thread(runner);
    }

    /**
     * Defines an interface for a callback that will handle
     * responses from the thread loader when an image is done
     * being loaded.
     */
    public interface ImageLoadedListener {
        public void imageLoaded(Bitmap imageBitmap );
    }

    /**
     * Provides a Runnable class to handle loading
     * the image from the URL and settings the
     * ImageView on the UI thread.
     */
    private class QueueRunner implements Runnable {
        public void run() {
            synchronized(this) {
                while(Queue.size() > 0) {
                    final QueueItem item = Queue.remove(0);

                    // If in the cache, return that copy and be done
                    if( Cache.containsKey(item.url.toString()) && Cache.get(item.url.toString()) != null) {
                        // Use a handler to get back onto the UI thread for the update
                        handler.post(new Runnable() {
                            public void run() {
                                if( item.listener != null ) {
                                    // NB: There's a potential race condition here where the cache item could get
                                    //     garbage collected between when we post the runnable and it's executed.
                                    //     Ideally we would re-run the network load or something.
                                    SoftReference<Bitmap> ref = Cache.get(item.url.toString());
                                    if( ref != null ) {
                                        item.listener.imageLoaded(ref.get());
                                    }
                                }
                            }
                        });
                    } else {
                        final Bitmap bmp = readBitmapFromNetwork(item.url);
                        if( bmp != null ) {
                            Cache.put(item.url.toString(), new SoftReference<Bitmap>(bmp));

                            // Use a handler to get back onto the UI thread for the update
                            handler.post(new Runnable() {
                                public void run() {
                                    if( item.listener != null ) {
                                        item.listener.imageLoaded(bmp);
                                    }
                                }
                            });
                        }

                    }

                }
            }
        }
    }

    /**
     * Queues up a URI to load an image from for a given image view.
     *
     * @param uri   The URI source of the image
     * @param callback  The listener class to call when the image is loaded
     * @throws MalformedURLException If the provided uri cannot be parsed
     * @return A Bitmap image if the image is in the cache, else null.
     */
    public Bitmap loadImage( final String uri, final ImageLoadedListener listener) throws MalformedURLException {
        // If it's in the cache, just get it and quit it
        if( Cache.containsKey(uri)) {
            SoftReference<Bitmap> ref = Cache.get(uri);
            if( ref != null ) {
                return ref.get();
            }
        }

        QueueItem item = new QueueItem();
        item.url = new URL(uri);
        item.listener = listener;
        Queue.add(item);

        // start the thread if needed
        if( thread.getState() == State.NEW) {
            thread.start();
        } else if( thread.getState() == State.TERMINATED) {
            thread = new Thread(runner);
            thread.start();
        }
        return null;
    }

    /**
     * Convenience method to retrieve a bitmap image from
     * a URL over the network. The built-in methods do
     * not seem to work, as they return a FileNotFound
     * exception.
     *
     * Note that this does not perform any threading --
     * it blocks the call while retrieving the data.
     *
     * @param url The URL to read the bitmap from.
     * @return A Bitmap image or null if an error occurs.
     */
    public static Bitmap readBitmapFromNetwork( URL url ) {
        InputStream is = null;
        BufferedInputStream bis = null;
        Bitmap bmp = null;
        try {
            URLConnection conn = url.openConnection();
            conn.connect();
            is = conn.getInputStream();
            bis = new BufferedInputStream(is);
            bmp = BitmapFactory.decodeStream(bis);
        } catch (MalformedURLException e) {
            Log.e(TAG, "Bad ad URL", e);
        } catch (IOException e) {
            Log.e(TAG, "Could not get remote ad image", e);
        } finally {
            try {
                if( is != null )
                    is.close();
                if( bis != null )
                    bis.close();
            } catch (IOException e) {
                Log.w(TAG, "Error closing stream.");
            }
        }
        return bmp;
    }

}

那么 Lthe Adpater 类可能如下所示：

public class ProjectAdapter extends ArrayAdapter<Project> {

    int resource;
    String response;
    Context context;
    private final static String TAG = "MediaItemAdapter";

    private ImageThreadLoader imageLoader = new ImageThreadLoader();



    //Initialize adapter
    public ProjectAdapter(Context context, int resource, List<Project> items) {
        super(context, resource, items);
        this.resource=resource;

    }



    @Override
    public View getView(int position, View convertView, ViewGroup parent)
    {

        TextView textTitle;
        final ImageView image;

        Project pro = getItem(position);

        LinearLayout projectView;
      //Inflate the view
        if(convertView==null)
        {
            projectView = new LinearLayout(getContext());
            String inflater = Context.LAYOUT_INFLATER_SERVICE;
            LayoutInflater vi;
            vi = (LayoutInflater)getContext().getSystemService(inflater);
            vi.inflate(resource, projectView, true);
        }
        else
        {
            projectView = (LinearLayout) convertView;
        }

        try {
          textTitle = (TextView)projectView.findViewById(R.id.txt_title);
          image = (ImageView)projectView.findViewById(R.id.image);
        } catch( ClassCastException e ) {
          Log.e(TAG, "Your layout must provide an image and a text view with ID's icon and text.", e);
          throw e;
        }


        Bitmap cachedImage = null;
        try {
          cachedImage = imageLoader.loadImage(pro.smallImageUrl, new ImageLoadedListener() {
          public void imageLoaded(Bitmap imageBitmap) {
          image.setImageBitmap(imageBitmap);
          notifyDataSetChanged();                }
          });
        } catch (MalformedURLException e) {
          Log.e(TAG, "Bad remote image URL: " + pro.smallImageUrl, e);
        }

        textTitle.setText(pro.project_title);

        if( cachedImage != null ) {
          image.setImageBitmap(cachedImage);
        }

        return projectView;
    }

}