在Android（初级水平）Listview上延迟加载图像？ [重复]

5 回答

• 0

  Praveen -

  正如您已经在此发现我的博客文章，我只是想将其推回到Stackoverflow，以便其他人可以使用它 .

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

  还有一个我后来记录的类，它使用一个线程和一个回调来加载图像：

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

  Update: 为了解决您的特定异常，我认为 getChildAt 列表中返回的视图不是 ImageView - 它是用于保存图像和文本的任何布局视图 .

  Update to include relevant code :( Per @ george-stocker的推荐）

  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;
    }
  }
  

  回复于 2024-04-28T23:42:05+08:00
• 7

  我知道了 . 这是我想要的完美代码 . 延迟加载适用于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" };
    }
  

  回复于 2024-04-28T23:42:05+08:00
• 0

  据我了解，滚动完成后需要更新列表 . 这很简单 . 这是您的固定代码：

  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将告诉适配器重新显示所有可见项，因此它们将与image2一起显示 .

  回复于 2024-04-28T23:42:05+08:00
• 17

  据我所见，静态 ViewHolder 没有任何帮助 . 尝试将整个 onScrollStateChanged 函数放在 /* 和 */ 之间，删除 static ViewHolder 行，并将 holder = new ViewHolder(); 更改为 ViewHolder holder = new ViewHolder(); .

  回复于 2024-04-28T23:42:05+08:00
• 7

  啊，检查你的logcat以确保你的应用程序没有被杀死并重新启动 . 大多数手机将您的总应用程序大小限制为16mb或24mb . 很容易加载一堆图像，运行，杀死，重新启动，并让你的onPause不会在屏幕上加载大数据 . 这是穷人的收集 .

  回复于 2024-04-28T23:42:05+08:00