滚动ListView时图像顺序混乱

时间：2023-03-10 07:11:14
滚动ListView时图像顺序混乱

本文选自*（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。

滚动ListView时图像顺序混乱

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：

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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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@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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