在android(初学者级别)的Listview上延迟加载图像? [英] Lazy Load images on Listview in android(Beginner Level)?
问题描述
可能的重复:
Android - 我怎么做懒人ListView 中的图片加载
我正在使用自定义适配器处理列表视图.我想在其上加载图像和文本视图.图片是从互联网网址加载的.我只想向 hte 用户显示可见列表项的图像.我参考了 从 romainguy 上架了开源项目示例，但是理解代码很复杂.对于初学者，我只想知道如何处理适配器和活动之间的标签.来自 commonsware example 我可以在adapter上设置标签，但是在listview的空闲状态下无法显示相应的图像.请帮助我提出您的想法.示例代码更易于理解.
I am working on the listview with the custom adapter. I want to load the images and text view on it. The images are load from the internet urls. I just want to show the images which are visible list item to hte user. I refered the Shelves opensource project example from romainguy, but its to complicated to understand the code. For a beginner level, I just want to know how to handle the tag between the adapter and activity. From the commonsware example I can set the tag on adapter, but can't show the corresponding image at the idle state of the listview. Please help me with your ideas. Sample codes are more understandable.
谢谢.
结合高效 和 慢 ApiDemos 中的Adapter 更有助于理解.
The combination of Efficient and Slow Adapter in ApiDemos is more helpful to understand.
在像这样的高效适配器示例上所做的更改:
changes done on efficient adapter example like this:
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"};
}
现在工作正常.但是当滚动状态时它没有正确重新加载图像.某些项目间隔不显示图像2.这是加载图像的正确顺序.但并非在列表的所有项目中.实体项目间隔之间发生不匹配.如何纠正?
It works fine now. But when the scrolling state its not reloading the image properly. some interval of items not shows the images2. that is the correct order of the images are loading. But not in all items of list. Mismatches happening between solid item intervals. how to correct it?
推荐答案
Praveen -
因为你已经找到了我的博文，我只是想把它推回 Stackoverflow 以便其他人可以使用它.
As you already found my blog post on this, I just wanted to push it back to Stackoverflow so that others can use it.
以下是基本讨论:http://ballardhack.wordpress.com/2010/04/05/loading-remote-images-in-a-listview-on-android/
我后来记录了一个类，它使用一个线程和一个回调来加载图像:
And there's a class I documented later that uses a thread and a callback to load the images:
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 ImageView —— 它是任何东西用于保存图像和文本的布局视图.
Update: To address your specific exception, I think that view returned in the list from getChildAt is not an ImageView -- it's whatever layout view you are using to hold the image and text.
更新以包含相关代码:(根据@george-stocker 的建议)
Update to include relevant code: (Per @george-stocker's recommendation)
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;
}
}
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