在Android（初学者级别）列表视图上的懒加载图像？

可能重复：
Android - 我如何在ListView中执行延迟加载的图像

我正在使用自定义适配器处理listview。 我想加载它的图像和文本视图。 这些图像是从互联网网址加载的。 我只是想显示可见列表项的图像来激发用户。 我提到了来自romainguy的Shelves开源项目示例，但它很难理解代码。 对于初学者级别，我只想知道如何处理适配器和活动之间的标签。 从commonsware的例子中，我可以在适配器上设置标签，但不能在listview的空闲状态下显示相应的图像。 请帮助我提出你的想法。 示例代码更容易理解。

谢谢。

编辑：

ApiDemos中的Efficient和Slow Adapter的组合更有助于理解。

有效的适配器示例所做的更改如下所示：

public class List14 extends ListActivity implements ListView.OnScrollListener {
// private TextView mStatus;

private static boolean mBusy = false;
static ViewHolder holder;

public static class EfficientAdapter extends BaseAdapter {
    private LayoutInflater mInflater;
    private Bitmap mIcon1;
    private Bitmap mIcon2;

    public EfficientAdapter(Context context) {
        // Cache the LayoutInflate to avoid asking for a new one each time.
        mInflater = LayoutInflater.from(context);

        // Icons bound to the rows.
        mIcon1 = BitmapFactory.decodeResource(context.getResources(),
                R.drawable.icon48x48_1);
        mIcon2 = BitmapFactory.decodeResource(context.getResources(),
                R.drawable.icon48x48_2);
    }

    /**
     * The number of items in the list is determined by the number of
     * speeches in our array.
     * 
     * @see android.widget.ListAdapter#getCount()
     */
    public int getCount() {
        return DATA.length;
    }

    /**
     * Since the data comes from an array, just returning the index is
     * sufficent to get at the data. If we were using a more complex data
     * structure, we would return whatever object represents one row in the
     * list.
     * 
     * @see android.widget.ListAdapter#getItem(int)
     */
    public Object getItem(int position) {
        return position;
    }

    /**
     * Use the array index as a unique id.
     * 
     * @see android.widget.ListAdapter#getItemId(int)
     */
    public long getItemId(int position) {
        return position;
    }

    /**
     * Make a view to hold each row.
     * 
     * @see android.widget.ListAdapter#getView(int, android.view.View,
     *      android.view.ViewGroup)
     */
    public View getView(int position, View convertView, ViewGroup parent) {
        // A ViewHolder keeps references to children views to avoid
        // unneccessary calls
        // to findViewById() on each row.

        // 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 = mInflater.inflate(R.layout.list_item_icon_text,
                    null);

            // Creates a ViewHolder and store references to the two children
            // views
            // we want to bind data to.
            holder = new ViewHolder();
            holder.text = (TextView) convertView.findViewById(R.id.text);
            holder.icon = (ImageView) convertView.findViewById(R.id.icon);

            convertView.setTag(holder);
        } else {
            // Get the ViewHolder back to get fast access to the TextView
            // and the ImageView.
            holder = (ViewHolder) convertView.getTag();
        }
        if (!mBusy) {
            holder.icon.setImageBitmap(mIcon1);

            // Null tag means the view has the correct data
            holder.icon.setTag(null);
        } else {
            holder.icon.setImageBitmap(mIcon2);

            // Non-null tag means the view still needs to load it's data
            holder.icon.setTag(this);
        }
        holder.text.setText(DATA[position]);

        // Bind the data efficiently with the holder.
        // holder.text.setText(DATA[position]);

        return convertView;
    }

    static class ViewHolder {
        TextView text;
        ImageView icon;
    }
}

private Bitmap mIcon1;
private Bitmap mIcon2;
@Override
public void onCreate(Bundle savedInstanceState) {
    mIcon1 = BitmapFactory.decodeResource(this.getResources(),
            R.drawable.icon48x48_1);
    mIcon2 = BitmapFactory.decodeResource(this.getResources(),
            R.drawable.icon48x48_2);
    super.onCreate(savedInstanceState);
    setListAdapter(new EfficientAdapter(this));
    getListView().setOnScrollListener(this);
}

public void onScroll(AbsListView view, int firstVisibleItem,
        int visibleItemCount, int totalItemCount) {
}

public void onScrollStateChanged(AbsListView view, int scrollState) {
    switch (scrollState) {
    case OnScrollListener.SCROLL_STATE_IDLE:
        mBusy = false;

        int first = view.getFirstVisiblePosition();
        int count = view.getChildCount();
        for (int i = 0; i < count; i++) {

            holder.icon = (ImageView) view.getChildAt(i).findViewById(
                    R.id.icon);
            if (holder.icon.getTag() != null) {
                holder.icon.setImageBitmap(mIcon1);
                holder.icon.setTag(null);
            } 
        }

        // mStatus.setText("Idle");
        break;
    case OnScrollListener.SCROLL_STATE_TOUCH_SCROLL:
        mBusy = true;
        // mStatus.setText("Touch scroll");
        break;
    case OnScrollListener.SCROLL_STATE_FLING:
        mBusy = true;
        // mStatus.setText("Fling");
        break;
    }
}
private static final String[] DATA = { "Abbaye de Belloc",
        "Abbaye du Mont des Cats", "Abertam", "Abondance", "Ackawi",
        "Acorn", "Adelost", "Affidelice au Chablis", "Afuega'l Pitu"};
}

现在它工作正常。 但是，当滚动状态不正确重新加载图像。 项目的某些间隔不显示图像2。 这是加载图像的正确顺序。 但不是列表中的所有项目。 固体项目间隔之间发生不匹配。 如何纠正它？

---

Praveen -

正如你已经发现我的博客文章，我只是想推回到Stackoverflow，以便其他人可以使用它。

以下是基本的讨论：http://ballardhack.wordpress.com/2010/04/05/loading-remote-images-in-a-listview-on-android/

还有一个我稍后记录的类，它使用线程和回调来加载图像：

http://ballardhack.wordpress.com/2010/04/10/loading-images-over-http-on-a-separate-thread-on-android/

更新：为了解决您的特定异常，我认为从getChildAt返回的列表中的视图不是一个ImageView - 它是您用来保存图像和文本的任何布局视图。

更新以包含相关的代码 :(按照@乔治 - 斯托克的建议）

这是我使用的适配器：

public class MediaItemAdapter extends ArrayAdapter<MediaItem> {
  private final static String TAG = "MediaItemAdapter";
  private int resourceId = 0;
  private LayoutInflater inflater;
  private Context context;

  private ImageThreadLoader imageLoader = new ImageThreadLoader();

  public MediaItemAdapter(Context context, int resourceId, List<MediaItem> mediaItems) {
    super(context, 0, mediaItems);
    this.resourceId = resourceId;
    inflater = (LayoutInflater)context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
    this.context = context;
  }

  @Override
  public View getView(int position, View convertView, ViewGroup parent) {

    View view;
    TextView textTitle;
    TextView textTimer;
    final ImageView image;

    view = inflater.inflate(resourceId, parent, false);

    try {
      textTitle = (TextView)view.findViewById(R.id.text);
      image = (ImageView)view.findViewById(R.id.icon);
    } catch( ClassCastException e ) {
      Log.e(TAG, "Your layout must provide an image and a text view with ID's icon and text.", e);
      throw e;
    }

    MediaItem item = getItem(position);
    Bitmap cachedImage = null;
    try {
      cachedImage = imageLoader.loadImage(item.thumbnail, new ImageLoadedListener() {
      public void imageLoaded(Bitmap imageBitmap) {
      image.setImageBitmap(imageBitmap);
      notifyDataSetChanged();                }
      });
    } catch (MalformedURLException e) {
      Log.e(TAG, "Bad remote image URL: " + item.thumbnail, e);
    }

    textTitle.setText(item.name);

    if( cachedImage != null ) {
      image.setImageBitmap(cachedImage);
    }

    return view;
  }
}

---

我知道了。 这是我想要的完美代码。 延迟加载工作到自定义适配器只是可见列表项的图标。 希望它对初学者有所帮助

public class List14 extends ListActivity implements ListView.OnScrollListener {
// private TextView mStatus;

private static boolean mBusy = false;
static ViewHolder holder;

public static class EfficientAdapter extends BaseAdapter {
    private LayoutInflater mInflater;
    private Bitmap mIcon1;
    private Bitmap mIcon2;
    private Context mContext;

    public EfficientAdapter(Context context) {
        // Cache the LayoutInflate to avoid asking for a new one each time.
        mInflater = (LayoutInflater) context
                .getSystemService(Context.LAYOUT_INFLATER_SERVICE);
        mContext = context;
        // Icons bound to the rows.
        mIcon1 = BitmapFactory.decodeResource(context.getResources(),
                R.drawable.icon48x48_1);
        mIcon2 = BitmapFactory.decodeResource(context.getResources(),
                R.drawable.icon48x48_2);
    }

    /**
     * The number of items in the list is determined by the number of
     * speeches in our array.
     * 
     * @see android.widget.ListAdapter#getCount()
     */
    public int getCount() {
        return DATA.length;
    }

    /**
     * Since the data comes from an array, just returning the index is
     * sufficent to get at the data. If we were using a more complex data
     * structure, we would return whatever object represents one row in the
     * list.
     * 
     * @see android.widget.ListAdapter#getItem(int)
     */
    public Object getItem(int position) {
        return position;
    }

    /**
     * Use the array index as a unique id.
     * 
     * @see android.widget.ListAdapter#getItemId(int)
     */
    public long getItemId(int position) {
        return position;
    }

    /**
     * Make a view to hold each row.
     * 
     * @see android.widget.ListAdapter#getView(int, android.view.View,
     *      android.view.ViewGroup)
     */
    public View getView(int position, View convertView, ViewGroup parent) {
        // A ViewHolder keeps references to children views to avoid
        // unneccessary calls
        // to findViewById() on each row.

        // 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 = mInflater.inflate(R.layout.list_item_icon_text,
                    parent, false);

            // Creates a ViewHolder and store references to the two children
            // views
            // we want to bind data to.
            holder = new ViewHolder();
            holder.text = (TextView) convertView.findViewById(R.id.text);
            holder.icon = (ImageView) convertView.findViewById(R.id.icon);

             convertView.setTag(holder);
        } else {
            // Get the ViewHolder back to get fast access to the TextView
            // and the ImageView.
             holder = (ViewHolder) convertView.getTag();
        }

        if (!mBusy) {

            holder.icon.setImageBitmap(mIcon1);

            // Null tag means the view has the correct data
            holder.icon.setTag(null);

        } else {
            holder.icon.setImageBitmap(mIcon2);

            // Non-null tag means the view still needs to load it's data
            holder.icon.setTag(this);
        }
        holder.text.setText(DATA[position]);

        // Bind the data efficiently with the holder.
        // holder.text.setText(DATA[position]);

        return convertView;
    }

    static class ViewHolder {
        TextView text;
        ImageView icon;
    }
}

private Bitmap mIcon1;
private Bitmap mIcon2;

@Override
public void onCreate(Bundle savedInstanceState) {
    mIcon1 = BitmapFactory.decodeResource(this.getResources(),
            R.drawable.icon48x48_1);
    mIcon2 = BitmapFactory.decodeResource(this.getResources(),
            R.drawable.icon48x48_2);
    super.onCreate(savedInstanceState);
    setListAdapter(new EfficientAdapter(this));
    getListView().setOnScrollListener(this);
}

public void onScroll(AbsListView view, int firstVisibleItem,
        int visibleItemCount, int totalItemCount) {
}

public void onScrollStateChanged(AbsListView view, int scrollState) {
    switch (scrollState) {
    case OnScrollListener.SCROLL_STATE_IDLE:
        mBusy = false;

        int first = view.getFirstVisiblePosition();
        int count = view.getChildCount();

        for (int i = 0; i < count; i++) {

            holder.icon = (ImageView) view.getChildAt(i).findViewById(
                    R.id.icon);
            if (holder.icon.getTag() != null) {
                holder.icon.setImageBitmap(IMAGE[first+i]);// this is the image url array.
                holder.icon.setTag(null);
            }
        }

        // mStatus.setText("Idle");
        break;
    case OnScrollListener.SCROLL_STATE_TOUCH_SCROLL:
        mBusy = true;
        // mStatus.setText("Touch scroll");
        break;
    case OnScrollListener.SCROLL_STATE_FLING:
        mBusy = true;
        // mStatus.setText("Fling");
        break;
    }
}

private static final String[] DATA = { "Abbaye de Belloc",
        "Abbaye du Mont des Cats", "Abertam", "Abondance", "Ackawi",
        "Acorn", "Adelost", "Affidelice au Chablis", "Afuega'l Pitu",
        "Yarra Valley Pyramid", "Yorkshire Blue", "Zamorano",
        "Zanetti Grana Padano", "Zanetti Parmigiano Reggiano" };
  }

---

据我所知，你需要在滚动完成后更新你的列表。 这很容易。 以下是您的固定代码：

EfficientAdapter adapter;

@Override
public void onCreate(Bundle savedInstanceState) {
    mIcon1 = BitmapFactory.decodeResource(this.getResources(),
            R.drawable.icon48x48_1);
    mIcon2 = BitmapFactory.decodeResource(this.getResources(),
            R.drawable.icon48x48_2);
    super.onCreate(savedInstanceState);
    adapter=new EfficientAdapter(this);
    setListAdapter(adapter);
    getListView().setOnScrollListener(this);
}

public void onScroll(AbsListView view, int firstVisibleItem,
    int visibleItemCount, int totalItemCount) {
}

public void onScrollStateChanged(AbsListView view, int scrollState) {
    switch (scrollState) {
    case OnScrollListener.SCROLL_STATE_IDLE:
        mBusy = false;
        adapter.notifyDataSetChanged() 
        break;
    case OnScrollListener.SCROLL_STATE_TOUCH_SCROLL:
        mBusy = true;
        // mStatus.setText("Touch scroll");
        break;
    case OnScrollListener.SCROLL_STATE_FLING:
        mBusy = true;
        // mStatus.setText("Fling");
        break;
    }
}

notifyDataSetChanged会通知适配器重新显示所有可见项目，因此它们将与image2一起显示。

链接地址: http://www.djcxy.com/p/93117.html

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