Question

我一直有这个问题很长一段时间了。我一点一点地到达那里，但我没有太多时间花在编程上:(

所以我不得不从URL加载图像以便在列表视图中显示，而我几乎就在那里。它们是延迟加载的，我使用的缓存系统运行良好。问题是，当我开始滚动时，下载的图像位于错误的位置，我无法弄清楚我哪里出错了。

代码的灵感来自以下两个链接：这个用于布局的想法 http://blog.blundell-apps.com/imageview-with-loading-spinner/
这个用于缓存系统 http://android-developers.blogspot.fr/2010/07/multithreading-for-performance.html

所以这是我的代码：

public class LoaderImageView extends LinearLayout
{

private static final String TAG = "LoderImageView";

private Context mContext;

private ImageView mImage;
private ProgressBar mSpinner;


/* The HashMap that contains the references to the different 
 * downloads currently running.
 */
public static HashMap<LoaderImageView, BitmapDownloaderTask> tasks =
        new LinkedHashMap<LoaderImageView, BitmapDownloaderTask>();

public LoaderImageView(Context context, AttributeSet attrs)
{
    super(context, attrs);
    mContext = context;

    mImage = new ImageView(mContext);
    mImage.setLayoutParams(new LayoutParams(LayoutParams.WRAP_CONTENT,
            LayoutParams.WRAP_CONTENT));

    mSpinner = new ProgressBar(mContext);
    mSpinner.setLayoutParams(new LayoutParams(LayoutParams.WRAP_CONTENT,
            LayoutParams.WRAP_CONTENT));

    mSpinner.setIndeterminate(true);


    addView(mSpinner);
    addView(mImage);

    Log.w(TAG, "Loading an imageView");
}

public void downloadImage(String url)
{
    resetPurgeTimer();

    //Log.w(TAG, "Loading: " + url);

    if(url.equals(""))
    {
        mImage.setImageDrawable(mContext.getResources().getDrawable(R.drawable.male));
    }
    else
    {

        Bitmap bitmap = getBitmapFromCache(url);

        if(bitmap == null)
        {
            /* The bitmap is not in the cache. */
            cancelPotentialDownload(this);

            /* Start the new download. */
            BitmapDownloaderTask bdt = new BitmapDownloaderTask(this, url);
            bdt.execute();
        }
        else
        {
            /*The bitmap is in the cache. */
            mImage.setImageBitmap(bitmap);
            mSpinner.setVisibility(View.GONE);
        }
    }

}

class BitmapDownloaderTask extends AsyncTask<Void, Void, Bitmap>
{
    private String mUrl;
    private LoaderImageView mLiv;

    public BitmapDownloaderTask(LoaderImageView liv, String url)
    {
        mLiv = liv;
        mUrl = url;
    }

    @Override
    protected void onPreExecute()
    {
        LoaderImageView.tasks.put(mLiv, this);
        mSpinner.setVisibility(View.VISIBLE);
        mImage.setVisibility(View.GONE);
        Log.w(TAG, "Starting an AsyncTask");
    }


    @Override
    protected Bitmap doInBackground(Void... voids)
    {
        URL url = null;

        try
        {
            url = new URL(mUrl);
        }
        catch (MalformedURLException e)
        {
            e.printStackTrace();
        }

        return BitmapTools.fetchBitmap(url);
    }


    @Override
    protected void onPostExecute(Bitmap bitmap)
    {
        BitmapDownloaderTask b = tasks.get(mLiv);

        if(b == this)
        {
            LoaderImageView.tasks.remove(this);
            mImage.setImageBitmap(bitmap);
        }

        if (isCancelled())
        {
            bitmap = null;
        }

        addBitmapToCache(mUrl, bitmap);
        tasks.remove(mLiv);
        mSpinner.setVisibility(View.GONE);
        mImage.setVisibility(View.VISIBLE);
    }
}

/ *更多方法也与缓存有关... * /

这里是 xml 布局：

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="60dp"
    android:background="@drawable/list_item_selector" >

    <com.myproject.liste.LoaderImageView
        android:id="@+id/visites_image"
        android:layout_width="50dp"
        android:layout_height="50dp"
        android:layout_alignParentLeft="true"
        android:layout_centerVertical="true" />
</RelativeLayout>

我正在使用BaseAdapter和ListActivity创建列表。此外，我正在按数据页面加载列表：我加载了10个项目，当用户向下滚动时我再加载10个项目，并调用notifyDataSetChange（）;

在listView上延迟加载imageView

0 个答案: