2

我使用此示例中的 ListAdapter：

http://code.google.com/p/au-optimizing-layouts-201/source/browse/au_optimizinglayouts/src/com/example/android/training/optimizinglayouts/OptimizedListAdapter.java?r=4

这个例子不是很好，因为列表中的元素会根据我滚动的速度被绘制多次。那是因为只重用了一个

private FakeImageLoader mFakeImageLoader;

如果 FakeImageLoader.java getImage() 将加载真实图像。需要做什么才能让这个示例运行并保持性能？

public class OptimizedListAdapter extends BaseAdapter{

        ...
        private FakeImageLoader mFakeImageLoader;

public OptimizedListAdapter(Context cxt)
        {
                // Cache the LayoutInflate to avoid asking for a new one each time.
                mLayoutInflater = LayoutInflater.from(cxt);
                mFakeImageLoader = new FakeImageLoader(cxt);
                ...

 public View getView(final int position, View convertView, ViewGroup parent)
        {
        // A ViewHolder keeps references to children views to avoid unneccessary calls
        // to findViewById() on each row.
        ViewHolder holder;

                // When convertView is not null, we can reuse it directly, there is no need
        // to reinflate it. We only inflate a new View when the convertView supplied
        // by ListView is null.
                if(convertView==null)
                {
                        convertView = mLayoutInflater.inflate(R.layout.listitem, null);

                        // Creates a ViewHolder and store references to the two children views
            // we want to bind data to.
            holder = new ViewHolder();
            holder.icon = (ImageView) convertView.findViewById(R.id.listitem_image);
            holder.text = (TextView) convertView.findViewById(R.id.listitem_text);
            holder.timestamp = (TextView) convertView.findViewById(R.id.listitem_timestamp);
            convertView.setTag(holder);
                }else
                {
                        holder = (ViewHolder) convertView.getTag();
                }

                //holder.icon.setImageDrawable(drawable);
                holder.text.setText(new StringBuffer(ITEM_PRE_TEXT).append(position));
                holder.timestamp.setText(""+(System.currentTimeMillis()-START_TIMESTAMP));
        holder.position = position;

        //during a fast scroll this could start 100's of threads, need a thread pool processing them!
        //see previous ImageLoader.
                new AsyncTask<ViewHolder, Void, Bitmap>() {
                        private ViewHolder v;

                        @Override
                        protected Bitmap doInBackground(ViewHolder... params) {
                                v = params[0];
                                return mFakeImageLoader.getImage();
                        }

                        @Override
                        protected void onPostExecute(Bitmap result) {
                                super.onPostExecute(result);
                                if(v.position == position)
                                {
                                        v.icon.setImageBitmap(result);
                                }
                        }

                  }.execute(holder);
                  //holder.icon.setImageBitmap(mFakeImageLoader.getImage());

                return convertView;
        }

谢谢塔塔

4

2 回答 2

1

我在一个应用程序中使用了这个通用图像加载器库通用图像加载器库来下载图像，它对我来说更有用。

于 2013-01-28T18:46:28.790 回答
0

这就是我用于延迟加载的方法。请注意，此代码已修改（删除了您不需要查看 xD 的内容）并且没有经过测试，只是为了分享这个想法。

import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;


public final class ResultsAdapter
        extends BaseAdapter
{

    // this is used for runnint on UI thread, as View.post did not always executed for me
    private Activity host;
    private ExecutorService service;

    public ResultsAdapter(Activity host)
    {
        this.host = host;
    }

    /**
     *  Set new data to this adapter. Or if your data will not change, you can do this in constructor
     */
    public void refresh(List<MyClass> data)
    {
        if (this.service != null) {
            this.service.shutdownNow();
        }

        this.data = data;

        this.service = Executors.newSingleThreadExecutor();
        this.notifyDataSetChanged();
    }

    @Override
    public View getView(int position, View convertView, ViewGroup parent)
    {
        ...
        MyClass item = items.get(position);
        holder.image.setTag(Long.valueOf(item.getId()));
         try {
            this.service.submit(new Job(current.getImageURL(), h.logo, Long.valueOf(item.getId())));
        } catch (Throwable e) {
        }
        ...

    }


    private final class Job
            implements Runnable
    {

        private final ImageView logo;
        private final Long logoTag;
        private final String URL;

        private Job(String url; ImageView logo, Long logoTag)
        {
            this.URL = url;
            this.logo = logo;
            this.logoTag = logoTag;
        }

        @Override
        public void run()
        {
            Thread t = Thread.currentThread();
            t.setPriority(Thread.NORM_PRIORITY - 1); //not to load ui thread much
            ...
            //load my stuff
            ...
            // logo tag could change during scrolling. getView could be called for the same reused view, so we check if we are not currently setting old data.
            if (logo.getTag().equals(logoTag)) {
                host.runOnUiThread(new Runnable()
                {
                    @Override
                    public void run()
                    {
                        logo.setImageBitmap(myStuff);
                    }
                }
            });
        }
    }
}

但是我在快速滚动过程中仍然遇到一些数据变化。告诉我这是否使它不那么引人注目。

于 2013-01-29T09:18:30.687 回答