我正在尝试使用 volley 库。我得到它来下载一组项目，将它们放入列表视图并加载每个项目都可以的远程图像。受此鼓舞，我尝试实现一个连续的列表视图，这样我就可以放弃分页控件。
我要从中请求数据的网站在页面中提供数据，每个页面有 10 个项目，因此我在我的 adapter.getView 上添加了一个检查，以便在页面结束之前位置为 2（第 1 页的位置 8，第 18 页的位置第 2 页等），它应该加载一个新页面并将新项目附加到列表的末尾。它有效，但行为不是我所期望的。
第一页加载正常，图像加载需要几秒钟，但没关系。然后，当我向下滚动时，当它加载新页面时，所有已经显示的图像都消失了，尽管它们与新的图像一起再次出现。也就是说，它加载好的前 10 张图片，然后“打嗝”使它们消失，然后它们与接下来的 10 张图片一起重新出现。但是，数据加载正常并且不会消失或类似的东西。
这是我的 ArrayAdapter
public class ItemAdapter extends ArrayAdapter<Item> implements Listener<JSONObject>, ErrorListener{
private static final String TAG = VolleyTestApp.LOGTAG;
private final Context mCtx;
private final ArrayList<Item> items;
//private int elegido = -1;
ItemsViewHolder viewHolder;
/**********************************/
private int pageSize = 0;
private int currentPage = 0;
private boolean mLoading = false;
private RequestQueue rq;
private ItemsListRequestParameter params;
public ItemAdapter(Context context, int resource,
List<Item> objects) {
super(context, resource,
objects);
mCtx = context;
items = (ArrayList<Item>) objects;
rq = SingletonRequestQueue.getInstance(mCtx);
}
public View getView(int position, View convertView, ViewGroup parent) {
View v = convertView;
LayoutInflater vi = ((Activity) mCtx).getLayoutInflater();
v = vi.inflate(R.layout.items_list_item, null);
viewHolder = new ItemsViewHolder(v);
Log.d(TAG, "Adapter viewholder creado " );
v.setTag(viewHolder);
viewHolder = (ItemsViewHolder) v.getTag();
Log.d(TAG, "Adapter posición: " + position);
if(viewHolder != null){
if (items.size() > 0){
Log.d(TAG, "Adapter tamaño lista: " + getCount());
Item t = items.get(position);
Log.d(TAG, "Adapter devolviendo item: " + items.get(position).getItemName());
String foto = t.getItemPicUrl();
if (foto == null || foto.equalsIgnoreCase("")){
viewHolder.itemPic.setImageResource(R.drawable.img_default_item_thumbnail);
}else{
Log.d(TAG, "Adapter devolviendo item foto: " + foto);
int cacheSize = getCacheSize();
Log.d(TAG, "Adapter cacheSize: " + cacheSize);
BitmapLruImageCache cache = new BitmapLruImageCache(cacheSize);
ImageLoader imgLoader =
new ImageLoader(SingletonRequestQueue.getInstance(mCtx),
cache);
viewHolder.itemPic.setImageUrl(foto, imgLoader);
}
viewHolder.itemName.setText(t.getItemName());
viewHolder.itemData1.setText(t.getData1());
}
}else{
Log.d(TAG, "Adapter viewHolder null: " );
}
/**************************************************/
Log.d(TAG, "Adapter.getView posición: " + position + "; pageSize: " + pageSize + "; currentPage: " + currentPage);
if (position +2 == (this.pageSize * (this.currentPage +1) )&& !mLoading){
Log.d(TAG, "Adapter.getView pidiendo nuevos datos");
if(this.params == null){
Log.w(TAG, "Adapter.getView params null " );
}else{
Log.w(TAG, "Adapter.getView nueva carga" );
this.params.nextPage();
this.loadData(this.params, pageSize);
}
}
return v;
}
public int getCacheSize() {
final DisplayMetrics displayMetrics = mCtx.getResources().getDisplayMetrics();
final int screenWidth = displayMetrics.widthPixels;
final int screenHeight = displayMetrics.heightPixels;
final int screenBytes = screenWidth * screenHeight * 4; // 4 bytes per pixel
return screenBytes * 3;
}
@Override
public void add(Item object) {
items.add(object);
Log.d(TAG, "Item añadida a adapter: " + object.getItemName());
}
@Override
public void clear() {
//super.clear();
items.clear();
}
@Override
public int getCount() {
return items.size();
}
static class ItemsViewHolder{
TextView itemName;
TextView itemData1;
NetworkImageView itemPic;
LinearLayout container;
public ItemsViewHolder(View v){
this.itemName = (TextView) v.findViewById(R.id.lti_nombre_item);
this.itemData1 = (TextView) v.findViewById(R.id.lti_datos_item1);
this.itemPic = (NetworkImageView) v.findViewById(R.id.tli_r_img);
this.container = (LinearLayout) v.findViewById(R.id.lti_container);
}
}
public void loadData(ItemsListRequestParameter params, int pageSize){
mLoading = true;
ItemListRequest jr = new ItemListRequest(params, this, this);
this.pageSize = pageSize;
this.params = params;
this.rq.add(jr);
}
@Override
public void onErrorResponse(VolleyError error) {
Log.d(TAG, "Adapter.onErrorResponse request con error");
mLoading = false;
// TODO meter elemento con mensaje error
Log.i(TAG, "Adapter.onErrorResponse request respondida " + error.getMessage());
}
@Override
public void onResponse(JSONObject response) {
Log.d(TAG, "Adapter.onResponse request respondida " + response.toString());
mLoading = false;
Response tr = ResponseParser.parseUltimasItemsJSONresponse(response);
if (tr.getResponseCode().equalsIgnoreCase("000")){
DaoList tdl = (DaoList) tr.getResponseInfo();
this.currentPage = tdl.getCurrentPage();
Log.d(TAG, "Adapter.onResponse currentPage: " + currentPage);
Iterator<Dao> it = tdl.iterator();
//tta.clear();
while (it.hasNext()){
Item t = (Item) it.next();
this.add(t);
}
this.notifyDataSetChanged();
}
}
}
我的 ItemListRequest 子类化了 volley Request 的修改版本
基本请求
public class BaseRequest extends Request<JSONObject>{
private Listener<JSONObject> mListener;
public BaseRequest(int method,
String url,
Listener<JSONObject> successListener,
ErrorListener errorListener) {
super(method,url,errorListener);
this.mListener = successListener;
}
/**
* transform NetworkResponse into Response<JSONObject>
*/
@Override
protected Response<JSONObject> parseNetworkResponse(NetworkResponse response) {
try {
String jsonString =
new String(response.data, HttpHeaderParser.parseCharset(response.headers));
return Response.success(new JSONObject(jsonString),
HttpHeaderParser.parseCacheHeaders(response));
} catch (UnsupportedEncodingException e) {
return Response.error(new ParseError(e));
} catch (JSONException je) {
return Response.error(new ParseError(je));
}
}
/**
* Here we send the response to the successListener
*/
@Override
protected void deliverResponse(JSONObject response) {
this.mListener.onResponse(response);
}
}
后请求
public class PostRequest extends BaseRequest {
private Map<String, String> mParams;
private static int method = Method.POST;
public PostRequest(ItemsListRequestParameter params,
String url, Listener<JSONObject> successListener,
ErrorListener errorListener) {
super(method, url, successListener, errorListener);
this.mParams = params.getMappedParams();
}
/**
* Override getParams so that it returns our POST params
*/
@Override
protected Map<String, String> getParams() throws AuthFailureError {
return mParams;
}
}
还有 ItemListRequest，我在适配器中使用的实际请求
public class ItemListRequest extends PostRequest{
public ItemListRequest(TapasListRequestParameter params,
Listener<JSONObject> successListener,
ErrorListener errorListener) {
super( params, RequestData.SEARCH_TAPAS_LIST_URL,successListener, errorListener);
this.setShouldCache(Boolean.TRUE);
}
}
我真的不明白图像重新加载背后的原因。任何有关如何防止它的帮助将不胜感激。