Question

我正在尝试实现上传图片（Wireframe）中显示的活动（）。可能有n个这样的项目。（预计将实现延迟加载。）图像是ImageButtons，QTY（数量）是微调器。项目名称，项目价格和项目图像是从服务器获取的。

当我点击Item Image并点击qunatity spinner时，我期待一个不同的实现。当我使用listview + adapter实现它时，这是不可能的。（我跟着http://wptrafficanalyzer.in/blog/android-lazy-loading-images-and-text-in-listview-from-http-json-data/）

我希望图像将被加载到不同的线程中。

有谁能请给我一个如何解决这个问题的方向？我已经阅读了使用listview +适配器的足够实现。他们都没有帮助解决问题 Expected wireframe design

Answer 1

Lars在ListViews上有一个很棒的教程，并使用自定义适配器填充它们here。标题为“ListViews和性能”的部分应该是最有帮助的。

对于延迟加载，请查看Universal Image Loader。您所要做的就是在应用程序类中初始化图像加载器，然后在需要使用它的任何地方调用ImageLoader.getInstance()。使用.displayImage()会获取图片uri和ImageView。所有线程和位图解码都由库完成。它使得它非常简单并且具有大量额外的功能。

Answer 2

//文件缓存类

package com.imageloader;

import java.io.File;
import android.content.Context;

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(),"LazyList");
        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();
    }

}

// ImageLoader类

package com.imageloader;

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;

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_launcher;
    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 (Exception ex){
           ex.printStackTrace();
           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;
        }

        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();
    }

}

// MemoryCache Class

package com.imageloader;

import java.lang.ref.SoftReference;
import java.util.Collections;
import java.util.HashMap;
import java.util.Map;
import android.graphics.Bitmap;

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();
    }
}

// Utils class

package com.imageloader;

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){}
    }
}

//从BaseAdapter中的url获取图像以获取listview和GridView

package com.inflater;

import java.util.ArrayList;
import android.content.Context;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.BaseAdapter;
import android.widget.ImageView;
import android.widget.TextView;

import com.globaldata.Utilities;
import com.imageloader.ImageLoader;

public class MyAdapter extends BaseAdapter {

    private Context mContext;
    private ImageLoader mImageLoader;
    private ArrayList<Model> mArrayList = new ArrayList<Model>();
    private LayoutInflater mLayoutInflater;

    public VideoArrangeAdapter(Context ctx, ArrayList<Model> mData) {

        this.mContext = ctx;
        this.mArrayList = mData;
        this.mImageLoader = new ImageLoader(this.mContext);
        this.mLayoutInflater = (LayoutInflater) this.mContext
                .getSystemService(Context.LAYOUT_INFLATER_SERVICE);
    }

    @Override
    public int getCount() {

        return mArrayList.size();
    }

    @Override
    public Object getItem(int position) {

        return mArrayList.get(position);
    }

    @Override
    public long getItemId(int arg0) {

        return arg0;
    }

    private class ViewHolder {
        private ImageView iv_image;
        private TextView textview_title;

    }

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

        ViewHolder holder = null;

        if (convertView == null) {

            holder = new ViewHolder();
            convertView = mLayoutInflater.inflate(R.layout.item_of_listview,
                    null);
            holder.iv_image = (ImageView) convertView
                    .findViewById(R.id.iv_image);
            holder.textview_title = (TextView) convertView
                    .findViewById(R.id.textview_title);

            convertView.setTag(holder);
        } else {
            holder = (ViewHolder) convertView.getTag();
        }

        holder.textview_title.setText(mArrayList.get(position).get_title());
        mImageLoader.DisplayImage(mArrayList.get(position).get_thumb(),
                holder.iv_image);

        notifyDataSetChanged();

        return convertView;

    }

}

线性布局的延迟加载（图像+文本）

2 个答案: