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。
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：
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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);}@Overrideprotected 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。
可能是这个代码片段：
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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：
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final ViewHolder viewHolder; |
然后在if结构中：
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viewHolder = new
ViewHolder(); |
执行你的代码：
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@Overridepublic 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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