在两个活动之间传递图像的最快方法是什么？

Question

说我有：

Activityactivity1 包含ImageViewimageView1

和

Activityactivity2 包含ImageViewimageView2，

我有一个字符串 url 指向一个图像（由 Picasso 缓存），我已经将它加载到 imageView1 中。 如何以最快的方式启动 Activitiy2 并将相同的图像加载到 ImageView2 中？

目前，我会在活动启动后立即在网址上调用Picasso.load().into()。这很快，但我正在寻找更快的东西。

Picasso.with(mContext)
        .load(myUrl)
        .into(imageView2);

任何建议都将不胜感激。

Answer 1

毕加索下载完整图像并将原始图像保存在磁盘/内存中。假设原始图像尺寸为 800x800，并且您尝试将此图像加载到尺寸为：100x100 的视图中，那么 Picasso 将需要一些时间来重新调整大小。 您可能想尝试一下 Glide[1]。 Glide 可以选择缓存调整大小的图像和原始图像。 （检查 Glide#diskCachingStratedgy）

此外，对于 Picasso，如果您使用 .noFade() 选项，则图像加载速度可能会更快。

[1]https://inthecheesefactory.com/blog/get-to-know-glide-recommended-by-google/en

Answer 2

我认为它已经足够快了。 Picasso 只是从共享内存缓存中获取它，它被存储为准备使用的位图。它比使用 intent.putExtra("image".bitmapByteArray) 或使用带有解码或编码位图的文件更快。

Answer 3

您需要创建三个类来将图像存储在缓存中，并且加载图像的速度非常快。 1.ImageLoader.java 2. FileCache.java 3. MemoryCache.java

ImageLoader.java

package com.thefinal3.Camera;

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.widget.ImageView;

import com.thefinal3.R;
import com.thefinal3.Utils.Utils;

/**
 * Created by Akash patel on 03-05-2016.
 */
public class ImageLoader {

    MemoryCache memoryCache=new MemoryCache();
    FileCache fileCache;
    private Map<ImageView, String> imageViews=Collections.synchronizedMap(new WeakHashMap<ImageView, String>());
    ExecutorService executorService;

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

    final int stub_id= R.drawable.ic_no_image;
    public void DisplayImage(String url, ImageView imageView)
    {
        imageViews.put(imageView, url);
        Bitmap bitmap=memoryCache.get(url);
        if(bitmap!=null)
            imageView.setImageBitmap(bitmap);
        else
        {
            queuePhoto(url, imageView);
            imageView.setImageResource(stub_id);
        }
    }

    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;
            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;
        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() {
            if(imageViewReused(photoToLoad))
                return;
            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();
            a.runOnUiThread(bd);
        }
    }

    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);
            else
                photoToLoad.imageView.setImageResource(stub_id);
        }
    }

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

}

FileCache.java

package com.thefinal3.Camera;

import android.content.Context;

import java.io.File;

/**
 * Created by Akash patel on 03-05-2016.
 */
public class FileCache {

    private File cacheDir;

    public FileCache(Context context){
        //Find the dir to save cached images
        if (android.os.Environment.getExternalStorageState().equals(android.os.Environment.MEDIA_MOUNTED))
            cacheDir=new File(android.os.Environment.getExternalStorageDirectory(),"TTImages_cache");
        else
            cacheDir=context.getCacheDir();
        if(!cacheDir.exists())
            cacheDir.mkdirs();
    }

    public File getFile(String url){
        //I identify images by hashcode. Not a perfect solution, good for the demo.
        String filename=String.valueOf(url.hashCode());
        //Another possible solution (thanks to grantland)
        //String filename = URLEncoder.encode(url);
        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();
    }

}

MemoryCache.java

    package com.thefinal3.Camera;
    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;
                //NullPointerException sometimes happen here http://code.google.com/p/osmdroid/issues/detail?id=78
                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{
                //NullPointerException sometimes happen here http://code.google.com/p/osmdroid/issues/detail?id=78
                cache.clear();
                size=0;
            }catch(NullPointerException ex){
                ex.printStackTrace();
            }
        }

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

创建以上三个类后，您只需要像这样在 imageview 中加载图像：

ImageLoader imageLoader = new ImageLoader(activity);
            imageLoader.DisplayImage(bean.getPhotoURL(),holder.imgSelectedPhoto);

Answer 4

您能否提供“快速”（如 0.1 秒）的定量测​​量？你可以很容易地做到这一点 -

Intent intent = new Intent(this, NewActivity.class);
intent.putExtra("BitmapImage", bitmap);

并将其检索为 -

Intent intent = getIntent();
Bitmap bitmap = (Bitmap) intent.getParcelableExtra("BitmapImage");