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Android - How do I do a lazy load of images in ListView在Android（初學者級別）Listview中的懶加載圖像？
我的工作與自定義適配器列表視圖。我想加載它的圖像和文本視圖。這些圖像是從互聯網網址加載的。我只是想顯示可見列表項的圖像來激發用戶。我提到了Shelves opensource project example from romainguy，但它很難理解代碼。對於初學者級別，我只想知道如何處理適配器和活動之間的標籤。從commonswareexample我可以在適配器上設置標籤，但不能在列表視圖的空閒狀態下顯示相應的圖像。請幫助我提出你的想法。示例代碼更容易理解。
謝謝。
編輯：
Efficient和Slow適配器在ApiDemos的組合是更有助於理解。
變化對有效的適配器例如做過這樣的：
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"};
}
現在工作得很好。但是，當滾動狀態不正確重新加載圖像。項目的某些間隔不顯示圖像2。這是加載圖像的正確順序。但不是列表中的所有項目。固體項目間隔之間發生不匹配。 如何糾正它？
你知道如何獲得圖像視圖對象嗎？我看到並使用了你的代碼。但是，沒有正確加載圖像。一個或兩個圖像沒有完成丟失。並獲得Outofmemory異常。爲什麼？願你呢？ – Praveen 2010-05-28 08:46:40
您需要跟蹤您的視圖層次結構。在ListView上調用getChildAt（index）將返回可見列表頂部索引的列表視圖項（佈局視圖）。在該視圖對象上，您可以調用findViewById來獲取圖像視圖。 – jwadsack 2010-05-28 19:42:26
請從您的博客相關部分到這裏。沒有這一點，當這些鏈接死亡時，你的答案的有效性就會隨之消失。 – 2012-07-02 23:55:13