滚动ListView时图像顺序混乱

本文选自StackOverflow（简称：SOF）精选问答汇总系列文章之一，本系列文章将为读者分享国外最优质的精彩问与答，供读者学习和了解国外最新技术。本文将为读者讲解滚动ListView时图像顺序混乱的解决方法。

问题：

zeitgeist

ListView有两个TextViews 和一个ImageView。图片是从网上下载的，缓存在LruCache。当在ListView滚动时，图片会出现几秒钟的混乱。直到正确的图片完全加载之前是不应该有任何图片出现的。我发现了几个同样的问题，但是没人能帮助我。

这是我的代码：

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public class NewsAdapter extends BaseAdapter {     private static LayoutInflater inflater;     private List<Item> items = new LinkedList<Item>();     private LruCache<String, Bitmap> mMemoryCache;       public NewsAdapter(Context context) {         inflater = (LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);           // Bitmap Cache         final int maxMemory = (int) (Runtime.getRuntime().maxMemory() / 1024);         final int cacheSize = maxMemory / 8;         mMemoryCache = new LruCache<String, Bitmap>(cacheSize) {             @Override             protected int sizeOf(String key, Bitmap bitmap) {                 return getSizeInBytes(bitmap) / 1024;             }         };     }       public void add(Item item) {         items.add(item);     }       @Override     public View getView(int position, View convertView, ViewGroup parent) {         ViewHolder viewHolder = new ViewHolder();         if(convertView == null) {             convertView = inflater.inflate(R.layout.list_item_item, null);             viewHolder.ivPic = (ImageView) convertView.findViewById(R.id.ivPic);             viewHolder.tvTitle = (TextView) convertView.findViewById(R.id.tvTitle);             viewHolder.tvShortDesc = (TextView) convertView.findViewById(R.id.tvShortDesc);             convertView.setTag(viewHolder);         } else {             viewHolder = (ViewHolder) convertView.getTag();         }           final Item item = items.get(position);         viewHolder.tvTitle.setText(item.getTitle());         viewHolder.tvShortDesc.setText(Html.fromHtml(item.getShortDesc()));           Bitmap bitmap = mMemoryCache.get(item.getPicUrl());         if (bitmap != null) {             viewHolder.ivPic.setImageBitmap(bitmap);         } else {             GetBitmap gb = new GetBitmap(item.getPicUrl(), viewHolder.ivPic);             gb.execute();         }           return convertView;     }       static class ViewHolder {         ImageView ivPic;         TextView tvTitle;         TextView tvShortDesc;     }       @Override     public int getCount() {         return items.size();     }       @Override     public Item getItem(int position) {         return items.get(position);     }       @Override     public long getItemId(int position) {         return 0;     }       @SuppressLint("NewApi")     public static int getSizeInBytes(Bitmap bitmap) {         if(Build.VERSION.SDK_INT >= Build.VERSION_CODES.HONEYCOMB) {             return bitmap.getByteCount();         } else {             return bitmap.getRowBytes() * bitmap.getHeight();         }     }       private class GetBitmap extends AsyncTask<Void, Bitmap, Bitmap> {         private String url;         private ImageView ivPic;           public GetBitmap(String url, ImageView ivPic) {             this.url = url;             this.ivPic = ivPic;         }           @Override         protected Bitmap doInBackground(Void... params) {             Bitmap bitmap = null;             try {                 URL url = new URL(this.url);                 bitmap = BitmapFactory.decodeStream(url.openConnection().getInputStream());             } catch (Exception e) {                 e.printStackTrace();             }               return bitmap;         }           @Override         protected void onPostExecute(Bitmap bitmap) {             super.onPostExecute(bitmap);             if (bitmap != null) ivPic.setImageBitmap(bitmap);         }       }   }

如果谁能帮助我那就太好了！先谢过！

PS:我忘记了一些东西，请不要建议任何库，我想在不使用外部库的情况下完成它。

答案：

Rajesh CP

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public GetBitmap(String url, ImageView ivPic, int position) {     this.url = url;     this.ivPic = ivPic;     this.position = position;     ivPic.setTag(position);     ivPic.setImageBitmap(null); }   @Override protected void onPostExecute(Bitmap bitmap) {      super.onPostExecute(bitmap);      if(bitmap != null && ((Integer)getTag) == this.position)          ivPic.setImageBitmap(bitmap); }

问题在于你没有检查图像是否在同一位置。试试上面的代码，希望能帮到你。在代码中，我没有找到任何推动位图加载到缓存的代码。

user2365568

可能是这个代码片段：

1	ViewHolder viewHolder = new ViewHolder();

这个片段是在每次调用getView的时候，创建viewHolder的新实例。

试试用这个来代替：

1	final ViewHolder viewHolder;

然后在if结构中：

1	viewHolder = new ViewHolder();

执行你的代码：

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@Override public View getView(int position, View convertView, ViewGroup parent) {    final ViewHolder viewHolder;       if(convertView == null) {         convertView = inflater.inflate(R.layout.list_item_item, null);         viewHolder = new ViewHolder();         viewHolder.ivPic = (ImageView) convertView.findViewById(R.id.ivPic);         viewHolder.tvTitle = (TextView) convertView.findViewById(R.id.tvTitle);         viewHolder.tvShortDesc = (TextView) convertView.findViewById(R.id.tvShortDesc);         convertView.setTag(viewHolder);     } else {         viewHolder = (ViewHolder) convertView.getTag();     }       final Item item = items.get(position);     viewHolder.tvTitle.setText(item.getTitle());     viewHolder.tvShortDesc.setText(Html.fromHtml(item.getShortDesc()));       Bitmap bitmap = mMemoryCache.get(item.getPicUrl());     if (bitmap != null) {         viewHolder.ivPic.setImageBitmap(bitmap);     } else {         GetBitmap gb = new GetBitmap(item.getPicUrl(), viewHolder.ivPic);         gb.execute();     }       return convertView; }

原文链接：ListView - Images shuffle while scrolling

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