Question

我屏幕上有6个可见项目。这是我的第一项：

我想要的是当我滚动时，第7个将是这样的：

但是在更改回第7项的3本书之前，它立即显示第1项的3本书。我认为这个问题与listview的回收机制或缓存有关，但我不知道如何解决它。请教我！

这是我的代码：

Adapter.class：

public class MyAdapter extends BaseAdapter {

    private Context mContext;
    private int[] mResourceId;
    private ImageLoader mImageLoader;
    private int count = 0;
    private ArrayList<MyImageObject> mImageObjects;

    public MyAdapter(Context context, int[] resourceId,ArrayList<MyImageObject> imageObjects) {
        // TODO Auto-generated constructor stub
        mContext = context;
        mResourceId = resourceId;
        mImageLoader = new ImageLoader(mContext);
        mImageObjects = imageObjects;
    }

    @Override
    public int getCount() {
        // TODO Auto-generated method stub

        return mImageObjects.size();
    }

    @Override
    public Object getItem(int position) {
        // TODO Auto-generated method stub
        return null;
    }

    @Override
    public long getItemId(int position) {
        // TODO Auto-generated method stub
        return 0;
    }

    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
        // TODO Auto-generated method stub
        ViewHolder viewHolder;
        if (convertView == null) {
            LayoutInflater layoutInflater = LayoutInflater.from(mContext);
            convertView = layoutInflater.inflate(R.layout.item_listview, parent, false);
            viewHolder = new ViewHolder();
            viewHolder.img1 = (ImageView) convertView.findViewById(R.id.imageView1);
            viewHolder.img2 = (ImageView) convertView.findViewById(R.id.imageView2);
            viewHolder.img3 = (ImageView) convertView.findViewById(R.id.imageView3);
            viewHolder.pb1 = (ProgressBar) convertView.findViewById(R.id.progressBar1);
            viewHolder.pb2 = (ProgressBar) convertView.findViewById(R.id.progressBar2);
            viewHolder.pb3 = (ProgressBar) convertView.findViewById(R.id.progressBar3);
            convertView.setTag(viewHolder);
        } else {
            viewHolder = (ViewHolder) convertView.getTag();
        }

        Log.e("POSITION", ""+ position);
        mImageLoader.displayImage(mImageObjects.get(position),viewHolder.img1, viewHolder.img2, viewHolder.img3, viewHolder.pb1, viewHolder.pb2, viewHolder.pb3);

        return convertView;
    }

ImageLoader.class：

public class ImageLoader {

    private Handler mHandler;
    private Context mContext;
    private ImageCacher mImageCacher = new ImageCacher();
    private ExecutorService mExecutorService;
    final int stub_int = R.drawable.ic_launcher;

    public ImageLoader(Context context) {
        // TODO Auto-generated constructor stub
        mContext = context;
        mImageCacher = new ImageCacher();
        mHandler = new Handler();
        mExecutorService = Executors.newFixedThreadPool(3);
    }

    public void displayImage(MyImageObject imageObject,final ImageView img1,final ImageView img2,
        final ImageView img3,final ProgressBar pb1,final ProgressBar pb2,final ProgressBar pb3) {

        //Set Imageview invisible if there is no book
        if(imageObject.getmResourceId2() == 0){
            pb2.setVisibility(View.INVISIBLE);
            img2.setVisibility(View.INVISIBLE);
        }
        else{
            img2.setVisibility(View.VISIBLE);
        }

        //Set Imageview invisible if there is no book
        if(imageObject.getmResourceId3() == 0){
            pb3.setVisibility(View.INVISIBLE);
            img3.setVisibility(View.INVISIBLE);
        }else{
            img3.setVisibility(View.VISIBLE);
        }

        //Check if image is already in cache or not
        Bitmap bitmap1 = mImageCacher.get(imageObject.getmResourceId1());
        Bitmap bitmap2 = mImageCacher.get(imageObject.getmResourceId2());
        Bitmap bitmap3 = mImageCacher.get(imageObject.getmResourceId3());
        //--------------------------------------------------------//
        if (bitmap1 != null) {
            pb1.setVisibility(View.INVISIBLE);
            img1.setImageBitmap(bitmap1);
        } else {
            queuePhoto(imageObject.getmResourceId1(), img1,pb1);
        }
        //-------------------------------------------------------//
        if (bitmap2 != null) {
            pb2.setVisibility(View.INVISIBLE);
            img2.setImageBitmap(bitmap2);
        } else {
            queuePhoto(imageObject.getmResourceId2(), img2,pb2);
        }
        //-------------------------------------------------------//
        if (bitmap3 != null) {
            pb3.setVisibility(View.INVISIBLE);
            img3.setImageBitmap(bitmap3);
        } else {
            queuePhoto(imageObject.getmResourceId3(), img3,pb3);
        }
    }



    private void queuePhoto(int resourceId, ImageView imageView,ProgressBar pb) {

        PhotoToLoad photoToLoad = new PhotoToLoad(resourceId, imageView,pb);
        mExecutorService.submit(new PhotosLoader(photoToLoad));

    }

    private class PhotoToLoad {
        private int mResourceId;
        private ImageView mImageView;
        private ProgressBar mProgressBar;

        private PhotoToLoad(int r, ImageView i,ProgressBar pb) {
            mResourceId = r;
            mImageView = i;
            mProgressBar = pb;
        }
    }

    private class PhotosLoader implements Runnable {

        PhotoToLoad photoToLoad;

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

        @Override
        public void run() {
            try {
                Bitmap bmp = scaleImage(photoToLoad.mResourceId);
                mImageCacher.put(photoToLoad.mResourceId, bmp);
                BitmapDisplayer bd = new BitmapDisplayer(bmp, photoToLoad);
                mHandler.post(bd);
            } catch (Throwable e) {
                e.printStackTrace();
            }
        }
    }



    private class BitmapDisplayer implements Runnable {

        Bitmap bitmap;
        PhotoToLoad photoToLoad;

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

        @Override
        public void run() {
            if (bitmap != null) {
                photoToLoad.mProgressBar.setVisibility(View.INVISIBLE);
                photoToLoad.mImageView.setImageBitmap(bitmap);
            } else {
                photoToLoad.mImageView.setImageResource(stub_int);
            }
        }
    }


    public Bitmap scaleImage(int resId) {

        final BitmapFactory.Options options = new BitmapFactory.Options();
        options.inJustDecodeBounds = true;
        BitmapFactory.decodeResource(mContext.getResources(), resId, options);


        options.inSampleSize = calculateInSampleSize(options, 90, 130);


        options.inJustDecodeBounds = false;
        Bitmap bitmap = BitmapFactory.decodeResource(mContext.getResources(), resId, options);
        bitmap = Bitmap.createScaledBitmap(bitmap, 70, 90, true);
        return bitmap;
    }

    public static int calculateInSampleSize(BitmapFactory.Options options, int reqWidth, int reqHeight) {
        // Raw height and width of image
        final int height = options.outHeight;
        final int width = options.outWidth;
        int inSampleSize = 1;

        if (height > reqHeight || width > reqWidth) {

            final int heightRatio = Math.round((float) height / (float) reqHeight);
            final int widthRatio = Math.round((float) width / (float) reqWidth);

            inSampleSize = heightRatio < widthRatio ? heightRatio : widthRatio;
        }

        return inSampleSize;
    }


    public void clearCache() {
        mImageCacher.clear();
    }
}

最后是ImageCacher：

public class ImageCacher {
    private static final String TAG = "MemoryCache";

    private Map<Integer, Bitmap> cache = Collections
            .synchronizedMap(new LinkedHashMap<Integer, Bitmap>(10, 1.5f, true));

    private long size = 0;

    private long limit = 1000000;

    public ImageCacher() {
        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(int id) {
        try {
            if (!cache.containsKey(id))
                return null;

            return cache.get(id);

        } catch (NullPointerException e) {
            e.printStackTrace();
            return null;
        }
    }

    public void put(int id, Bitmap bitmap) {

        try {

            if (cache.containsKey(id)) {
                size -= getSizeInBytes(cache.get(id));
            } else {
                cache.put(id, bitmap);
                size += getSizeInBytes(bitmap);
                checkSize();
            }
        } catch (Throwable e) {
            e.printStackTrace();
        }
    }

    private void checkSize() {

        //If cache size exceed limit --> remove last item
        if (size > limit) {
            Iterator<Entry<Integer, Bitmap>> iter = cache.entrySet().iterator();
            while (iter.hasNext()) {
                Entry<Integer, 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 e) {
            e.printStackTrace();
        }
    }

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

Answer 1

尝试
public class X { public void xCall() { System.out.println("X method called"); } public void move(){ System.out.println("I'm in parent class"); } } public class Y extends X{ public void yCall() { System.out.println("Y method called"); } public void move(){ System.out.println("I'm in child class"); } }

在displayImage方法的开头

编辑1

使用图像加载器和缓存来显示图像资源很重且没用。

您可能应该在适配器中使用X a = new X(); X b = new Y(); a.move();// runs the method in X class b.move();//Runs the method in Y class

请帮我解决这个Listview问题

1 个答案: