Android图像缓存？

Question

你好我正在开发一个安卓程序。我不知道如何缓存图像。我的图片从网页加载。我已经在谷歌上搜索过这个，但我找不到与我的缓存系统类似的东西。我的系统是这样工作的； c 是显示的图像，x 是缓存的图像

x x x x c x x x

有人可以帮助我吗？谢谢

Answer 1

 Create Imageloader object like below and follow below step.

  ImageLoader loader = new ImageLoader(this);
  ImageView i =new ImageView(this);

   loader.DisplayImage("set image url here ",i, 0);

   add below four class file:


1)// ImageLoader.java

import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
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.content.Context;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.os.Handler;
import android.util.Log;
import android.view.View;
import android.widget.ImageView;

public class ImageLoader {

    MemoryCache memoryCache = new MemoryCache();
    FileCache fileCache;
    private Map<ImageView, String> imageViews = Collections
            .synchronizedMap(new WeakHashMap<ImageView, String>());
    ExecutorService executorService;
    Handler handler = new Handler();// handler to display images in UI thread
    int index=0;
    Context cxt;
    public ImageLoader(Context context) {
        cxt =context;
        fileCache = new FileCache(cxt);
        executorService = Executors.newFixedThreadPool(5);
    }

    public void DisplayImage(String url, ImageView imageView, int val) {
        index = val;
        if (url.equals("")||url.equals("NA")) {
            if (index == 1)
                imageView.setImageResource(R.drawable.noagent);
            else
                imageView.setImageResource(R.drawable.no_image_large);
            return;
        }

        imageViews.put(imageView, url);
        Bitmap bitmap = memoryCache.get(url);

        if (bitmap != null)
            imageView.setImageBitmap(bitmap);
        else {
            queuePhoto(url, imageView);
            imageView.setImageResource(R.drawable.loading);
        }
    }

    private void queuePhoto(String url, ImageView imageView) {
        PhotoToLoad p = new PhotoToLoad(url, imageView);
        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(30000);
            conn.setReadTimeout(30000);
            conn.setInstanceFollowRedirects(true);
            InputStream is = conn.getInputStream();
            OutputStream os = new FileOutputStream(f);
            Utils.CopyStream(is, os);
            os.close();
            bitmap = decodeFile(f);
            return bitmap;
        } catch (Throwable ex) {
            ex.printStackTrace();
            if (ex instanceof OutOfMemoryError)
                memoryCache.clear();
            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;
            FileInputStream stream1 = new FileInputStream(f);
            BitmapFactory.decodeStream(stream1, null, o);
            stream1.close();

            // Find the correct scale value. It should be the power of 2.
            final int REQUIRED_SIZE = 100;
            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;
            }

            if (scale >= 2) {
                scale /= 2;
            }

            // decode with inSampleSize
            BitmapFactory.Options o2 = new BitmapFactory.Options();
            o2.inSampleSize = scale;
            FileInputStream stream2 = new FileInputStream(f);
            Bitmap bitmap = BitmapFactory.decodeStream(stream2, null, o2);
            stream2.close();
            return bitmap;
        } catch (FileNotFoundException e) {
        } catch (IOException e) {
            e.printStackTrace();
        }
        return null;
    }

    // Task for the queue
    private class PhotoToLoad {
        public String url;
        public ImageView imageView;

        public PhotoToLoad(String u, ImageView i) {
            url = u;
            imageView = i;
        }
    }

    class PhotosLoader implements Runnable {
        PhotoToLoad photoToLoad;

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

        @Override
        public void run() {
            try {
                if (imageViewReused(photoToLoad))
                    return;
                Bitmap bmp = getBitmap(photoToLoad.url);
                memoryCache.put(photoToLoad.url, bmp);
                if (imageViewReused(photoToLoad))
                    return;
                BitmapDisplayer bd = new BitmapDisplayer(bmp, photoToLoad);
                handler.post(bd);
            } catch (Throwable th) {
                th.printStackTrace();
            }
        }
    }

    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;
            Log.i("index", index+"");
            if (bitmap != null)
                photoToLoad.imageView.setImageBitmap(bitmap);
            else if (index == 1)
                photoToLoad.imageView.setImageResource(R.drawable.noagent);
            else if (index == 2)
                photoToLoad.imageView.setVisibility(View.GONE);
            else
                photoToLoad.imageView
                        .setImageResource(R.drawable.no_image_large);
        }
    }

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

}



2) // MemoryCache.java

import java.util.Collections;
import java.util.Iterator;
import java.util.LinkedHashMap;
import java.util.Map;
import java.util.Map.Entry;

import android.graphics.Bitmap;
import android.util.Log;

public class MemoryCache {

    private static final String TAG = "MemoryCache";
    private Map<String, Bitmap> cache=Collections.synchronizedMap(
            new LinkedHashMap<String, Bitmap>(10,1.5f,true));//Last argument true for LRU ordering
    private long size=0;//current allocated size
    private long limit=1000000;//max memory in bytes

    public MemoryCache(){
        //use 25% of available heap size
        setLimit(Runtime.getRuntime().maxMemory()/4);
    }

    public void setLimit(long new_limit){
        limit=new_limit;
        Log.i(TAG, "MemoryCache will use up to "+limit/1024./1024.+"MB");
    }

    public Bitmap get(String id){
        try{
            if(!cache.containsKey(id))
                return null;
            return cache.get(id);
        }catch(NullPointerException ex){
            ex.printStackTrace();
            return null;
        }
    }

    public void put(String id, Bitmap bitmap){
        try{
            if(cache.containsKey(id))
                size-=getSizeInBytes(cache.get(id));
            cache.put(id, bitmap);
            size+=getSizeInBytes(bitmap);
            checkSize();
        }catch(Throwable th){
            th.printStackTrace();
        }
    }

    private void checkSize() {
        Log.i(TAG, "cache size="+size+" length="+cache.size());
        if(size>limit){
            Iterator<Entry<String, Bitmap>> iter=cache.entrySet().iterator();//least recently accessed item will be the first one iterated  
            while(iter.hasNext()){
                Entry<String, Bitmap> entry=iter.next();
                size-=getSizeInBytes(entry.getValue());
                iter.remove();
                if(size<=limit)
                    break;
            }
            Log.i(TAG, "Clean cache. New size "+cache.size());
        }
    }

    public void clear() {
        try{
            cache.clear();
            size=0;
        }catch(NullPointerException ex){
            ex.printStackTrace();
        }
    }

    long getSizeInBytes(Bitmap bitmap) {
        if(bitmap==null)
            return 0;
        return bitmap.getRowBytes() * bitmap.getHeight();
    }
}

3) //Utils.java

import java.io.InputStream;
import java.io.OutputStream;

public class Utils {
    public static void CopyStream(InputStream is, OutputStream os)
    {
        final int buffer_size=1024;
        try
        {
            byte[] bytes=new byte[buffer_size];
            for(;;)
            {
              int count=is.read(bytes, 0, buffer_size);
              if(count==-1)
                  break;
              os.write(bytes, 0, count);
            }
        }
        catch(Exception ex){}
    }
}


4) // FileCache.java


import java.io.File;

import android.content.Context;

public class FileCache {

    private File cacheDir;

    public FileCache(Context context){
        if (android.os.Environment.getExternalStorageState().equals(android.os.Environment.MEDIA_MOUNTED))
            cacheDir=new File(android.os.Environment.getExternalStorageDirectory(),"LazyList");
        else
            cacheDir=context.getCacheDir();
        if(!cacheDir.exists())
            cacheDir.mkdirs();
    }

    public File getFile(String url){
        String filename=String.valueOf(url.hashCode());
        File f = new File(cacheDir, filename);
        return f;
    }

    public void clear(){
        File[] files=cacheDir.listFiles();
        if(files==null)
            return;
        for(File f:files)
            f.delete();
    }

}

Answer 2

您可以使用Android Smart Image View

myImage.setImageUrl("http://www.awesomeimages.com/myawesomeimage.jpg");

Answer 3

android.net.http.HttpResponseCache 是迄今为止最容易使用的缓存。

在 onCreate 中调用它

private void enableHttpResponseCache() {
        try {
            long httpCacheSize = 10 * 1024 * 1024; // 10 MiB
            File httpCacheDir = new File(getCacheDir(), "http");
            Class.forName("android.net.http.HttpResponseCache")
                    .getMethod("install", File.class, long.class)
                    .invoke(null, httpCacheDir, httpCacheSize);
        } catch (Exception httpResponseCacheNotAvailable) {
            Log.d("no cache", "HTTP response cache is unavailable.");
        }
    }