Question

我使用ImageLoader获取图像并显示进度条直到下载图像。 ArrayAdapter使用此类将图像加载到GridView。

我想知道当加载此gridview的片段已从活动中分离时如何释放图像内存。此外，如果在加载此视图后发生多个片段转换，将它存储在内存（即后台堆栈）中是否很昂贵。

这是我的代码

import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.InputStream;
import java.io.OutputStream;
import java.net.HttpURLConnection;
import java.net.URL;
import java.util.Collections;
import java.util.Map;
import java.util.WeakHashMap;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import android.app.Activity;
import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.util.Log;
import android.view.View;
import android.widget.ImageView;
import android.widget.ProgressBar;

public class ImageLoader {

    MemoryCache memoryCache = new MemoryCache();
    FileCache fileCache;

    private Map<ImageView, String> imageViews = Collections
            .synchronizedMap(new WeakHashMap<ImageView, String>());
    ExecutorService executorService;
    Activity activity = null;

    public ImageLoader(Context context) {
        fileCache = new FileCache(context);
        executorService = Executors.newFixedThreadPool(5);
    }

    public void DisplayImage(String url, Activity activity,
            ImageView imageView, ProgressBar p) {
        imageViews.put(imageView, url);
        this.activity = activity;
        Bitmap bitmap = memoryCache.get(url);
        if (bitmap != null) {
            imageView.setImageBitmap(bitmap);
            imageView.setTag("loaded");
            imageView.setVisibility(View.VISIBLE);
            p.setVisibility(View.GONE);
        } else {
            queuePhoto(url, imageView, p);
            imageView.setImageResource(Utils.stub_id);
        }
    }



    private void queuePhoto(String url, ImageView imageView, ProgressBar pb) {
        PhotoToLoad p = new PhotoToLoad(url, imageView, activity, pb);
        executorService.submit(new PhotosLoader(p));
    }

    private Bitmap getBitmap(String url) {
        File f = fileCache.getFile(url);

        // from SD cache
        Bitmap b = decodeFile(f);
        if (b != null)
            return b;

        // from web
        try {
            Bitmap bitmap = null;
            URL imageUrl = new URL(url);
            HttpURLConnection conn = (HttpURLConnection) imageUrl
                    .openConnection();
            conn.setConnectTimeout(Utils.timeout);
            conn.setReadTimeout(Utils.timeout);
            conn.setInstanceFollowRedirects(true);
            InputStream is = conn.getInputStream();
            OutputStream os = new FileOutputStream(f);
            Utils.CopyStream(is, os);
            os.close();
            bitmap = decodeFile(f);
            return bitmap;
        } catch (Exception ex) {

            return null;
        }
    }

    // decodes image and scales it to reduce memory consumption
    private Bitmap decodeFile(File f) {
        try {
            // decode image size
            BitmapFactory.Options o = new BitmapFactory.Options();
            o.inJustDecodeBounds = true;
            BitmapFactory.decodeStream(new FileInputStream(f), null, o);

            // Find the correct scale value. It should be the power of 2.
            final int REQUIRED_SIZE = 70;
            int width_tmp = o.outWidth, height_tmp = o.outHeight;
            int scale = 1;
            while (true) {
                if (width_tmp / 2 < REQUIRED_SIZE
                        || height_tmp / 2 < REQUIRED_SIZE)
                    break;
                width_tmp /= 2;
                height_tmp /= 2;
                scale *= 2;
            }

            // decode with inSampleSize
            BitmapFactory.Options o2 = new BitmapFactory.Options();
            o2.inSampleSize = scale;
            return BitmapFactory.decodeStream(new FileInputStream(f), null, o2);
        } catch (FileNotFoundException e) {
        }
        return null;
    }

    // Task for the queue
    private class PhotoToLoad {
        public String url;
        public ImageView imageView;
        Activity activity;
        public ProgressBar progressBar;

        public PhotoToLoad(String u, ImageView i, Activity a, ProgressBar p) {
            url = u;
            imageView = i;
            activity = a;
            progressBar = p;
        }
    }

    class PhotosLoader implements Runnable {
        PhotoToLoad photoToLoad;

        PhotosLoader(PhotoToLoad photoToLoad) {
            this.photoToLoad = photoToLoad;
        }

        @Override
        public void run() {
            if (imageViewReused(photoToLoad))
                return;
            try {
                Bitmap bmp = getBitmap(photoToLoad.url);
                memoryCache.put(photoToLoad.url, bmp);
                if (imageViewReused(photoToLoad))
                    return;
                BitmapDisplayer bd = new BitmapDisplayer(bmp, photoToLoad);
                // Activity a = (Activity) photoToLoad.imageView.getContext();
                photoToLoad.activity.runOnUiThread(bd);
            } catch (Exception e) {
                String s = e.getMessage();
            }
        }
    }

    boolean imageViewReused(PhotoToLoad photoToLoad) {
        String tag = imageViews.get(photoToLoad.imageView);
        if (tag == null || !tag.equals(photoToLoad.url))
            return true;
        return false;
    }

    // Used to display bitmap in the UI thread
    class BitmapDisplayer implements Runnable {
        Bitmap bitmap;
        PhotoToLoad photoToLoad;

        public BitmapDisplayer(Bitmap b, PhotoToLoad p) {
            bitmap = b;
            photoToLoad = p;
        }

        public void run() {
            if (imageViewReused(photoToLoad))
                return;

            if (bitmap != null)
            {
                photoToLoad.imageView.setImageBitmap(bitmap);
                photoToLoad.imageView.setTag("loaded");
            }
            else
                photoToLoad.imageView.setImageResource(Utils.stub_id);

            photoToLoad.imageView.setVisibility(View.VISIBLE);
            photoToLoad.progressBar.setVisibility(View.GONE);
        }

    }

    public void clearCache() {
        memoryCache.clear();
        fileCache.clear();
    }

   }

public class MemoryCache {
    private Map<String, SoftReference<Bitmap>> cache=Collections.synchronizedMap(new HashMap<String, SoftReference<Bitmap>>());

    public Bitmap get(String id){
        if(!cache.containsKey(id))
            return null;
        SoftReference<Bitmap> ref=cache.get(id);
        return ref.get();
    }

    public void put(String id, Bitmap bitmap){
        cache.put(id, new SoftReference<Bitmap>(bitmap));
    }

    public void clear() {
        cache.clear();
    }
}

Answer 1

您可以使用此方法

  MemoryCacheUtils.removeFromCache(url,ImageLoader.getInstance().getMemoryCache());
  DiscCacheUtils.removeFromCache(url, ImageLoader.getInstance().getDiscCache());

或者您可以通过

直接完成

imageLoader.clearMemoryCache();

`

在android上释放Image Loader的内存

1 个答案: