我正在创建一个应用程序，其中包含许多从JSON文件加载的产品。一切都很好，但我有一个小问题，我很难找到答案。只需单击一个按钮，我就可以从服务器上的JSON文件中获取所有数据（它包含一个URL值以获取产品的图片）。单击按钮时，我想立即移动到产品列表，只加载可见图像。相反，它需要大约8秒钟才能加载，并且它会预先加载所有图像。有人可以告诉我，我做错了什么？我在线阅读我应该使用类似的东西：imageLoader.DisplayImage（data [position]，image）;,但我使用的是Hashmap，而不仅仅是一个字符串。
这是我的代码，非常感谢任何帮助：
LazyAdapter
public class LazyAdapter extends BaseAdapter {
private Activity activity;
private ArrayList<HashMap<String, String>> data;
private static LayoutInflater inflater=null;
public ImageLoader imageLoader;
public LazyAdapter(Activity a, ArrayList<HashMap<String, String>> d) {
activity = a;
data=d;
inflater = (LayoutInflater)activity.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
imageLoader=new ImageLoader(activity.getApplicationContext());
}
public int getCount() {
return data.size();
}
public Object getItem(int position) {
return position;
}
public long getItemId(int position) {
return position;
}
public View getView(int position, View convertView, ViewGroup parent) {
View vi=convertView;
if(convertView==null)
vi = inflater.inflate(R.layout.list_row, null);
TextView brand = (TextView)vi.findViewById(R.id.brand); // title
TextView name = (TextView)vi.findViewById(R.id.name); // artist name
TextView price = (TextView)vi.findViewById(R.id.price); // duration
TextView imgValue = (TextView)vi.findViewById(R.id.imgValue);
//TextView rating = (TextView)vi.findViewById(R.id.rating); // rating
ImageView thumb_image=(ImageView)vi.findViewById(R.id.list_image); // thumb image
HashMap<String, String> products = new HashMap<String, String>();
products = data.get(position);
// Setting all values in listview
brand.setText(products.get(CustomizedListView.TAG_BRAND));
name.setText(products.get(CustomizedListView.TAG_NAME));
price.setText("£" + products.get(CustomizedListView.TAG_MIN_GBP));
imgValue.setText(products.get(CustomizedListView.TAG_IMG));
imgValue.setVisibility(View.GONE);
//rating.setText("Rating: " + song.get(CustomizedListView.TAG_RATING_NO) + "/5");
imageLoader.DisplayImage("http://debenhams.scene7.com/is/image/Debenhams/" + imgValue.getText() + "?hei=440&op_usm=1.1,0.5,0,0", thumb_image);
return vi;
}
}
的ListView
public class CustomizedListView extends Activity {
// All static variables
static final String link = "https://dl.dropboxusercontent.com/u/142838353/productlist.json";
// XML node keys
static final String TAG_PRODUCTS = "Products";
static final String TAG_PRODNUM = "prodnum";
static final String TAG_BRAND = "brand";
static final String TAG_NAME = "name"; // parent node
static final String TAG_MIN_GBP = "minGBP";
static final String TAG_IMG = "img";
static final String TAG_RATING_NO = "rating_number";
JSONArray products = null;
ListView list;
LazyAdapter adapter;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.shop);
// Hashmap for ListView
ArrayList<HashMap<String, String>> productList = new ArrayList<HashMap<String, String>>();
// Creating JSON Parser instance
JSONParser jParser = new JSONParser();
// getting JSON string from URL
JSONObject json = jParser.getJSONFromUrl(link);
try {
// Getting Array of Contacts
products = json.getJSONArray(TAG_PRODUCTS);
// looping through All Contacts
for(int i = 0; i < products.length(); i++){
JSONObject c = products.getJSONObject(i);
// Storing each json item in variable
// String prodnum = c.getString(TAG_PRODNUM);
String brand = c.getString(TAG_BRAND);
String name = c.getString(TAG_NAME);
String img = c.getString(TAG_IMG);
String price = c.getString(TAG_MIN_GBP);
//String ratingNo = c.getString(TAG_RATING_NO);
// creating new HashMap
HashMap<String, String> map = new HashMap<String, String>();
// adding each child node to HashMap key => value
map.put(TAG_MIN_GBP, price);
map.put(TAG_BRAND, brand);
map.put(TAG_NAME, name);
map.put(TAG_IMG, img);
//map.put(TAG_RATING_NO, ratingNo);
// adding HashList to ArrayList
productList.add(map);
}
} catch (JSONException e) {
e.printStackTrace();
}
list=(ListView)findViewById(R.id.list);
// Getting adapter by passing xml data ArrayList
adapter=new LazyAdapter(this, productList);
list.setAdapter(adapter);
// Click event for single list row
list.setOnItemClickListener(new OnItemClickListener() {
@Override
public void onItemClick(AdapterView<?> parent, View view,
int position, long id) {
String brand = ((TextView) view.findViewById(R.id.brand)).getText().toString();
String name = ((TextView) view.findViewById(R.id.name)).getText().toString();
String imgValue = ((TextView) view.findViewById(R.id.imgValue)).getText().toString();
String price = ((TextView) view.findViewById(R.id.price)).getText().toString();
//String imgVal = ((ImageView) view.findViewById(R.id.list_image)).;
//String imgVal = ((ImageView) view.findViewById(R.id.img)).getResources().toString();
// Starting new intent
Intent in = new Intent(getApplicationContext(), ProductActivity.class);
in.putExtra(TAG_BRAND, brand);
in.putExtra(TAG_NAME, name);
in.putExtra(TAG_IMG, imgValue);
in.putExtra(TAG_MIN_GBP, price);
startActivity(in);
}
});
}
@Override
public void onDestroy()
{
list.setAdapter(null);
super.onDestroy();
}
}
ImageLoader的
public class ImageLoader {
MemoryCache memoryCache=new MemoryCache();
FileCache fileCache;
private Map<ImageView, String> imageViews=Collections.synchronizedMap(new WeakHashMap<ImageView, String>());
ExecutorService executorService;
Handler handler=new Handler();//handler to display images in UI thread
public ImageLoader(Context context){
fileCache=new FileCache(context);
executorService=Executors.newFixedThreadPool(5);
}
final int stub_id=R.drawable.default_image;
public void DisplayImage(String url, ImageView imageView)
{
imageViews.put(imageView, url);
Bitmap bitmap=memoryCache.get(url);
if(bitmap!=null)
imageView.setImageBitmap(bitmap);
else
{
queuePhoto(url, imageView);
imageView.setImageResource(stub_id);
}
}
private void queuePhoto(String url, ImageView imageView)
{
PhotoToLoad p=new PhotoToLoad(url, imageView);
executorService.submit(new PhotosLoader(p));
}
private Bitmap getBitmap(String url)
{
File f=fileCache.getFile(url);
//from SD cache
Bitmap b = decodeFile(f);
if(b!=null)
return b;
//from web
try {
Bitmap bitmap=null;
URL imageUrl = new URL(url);
HttpURLConnection conn = (HttpURLConnection)imageUrl.openConnection();
conn.setConnectTimeout(30000);
conn.setReadTimeout(30000);
conn.setInstanceFollowRedirects(true);
InputStream is=conn.getInputStream();
OutputStream os = new FileOutputStream(f);
Utils.CopyStream(is, os);
os.close();
conn.disconnect();
bitmap = decodeFile(f);
return bitmap;
} catch (Throwable ex){
ex.printStackTrace();
if(ex instanceof OutOfMemoryError)
memoryCache.clear();
return null;
}
}
//decodes image and scales it to reduce memory consumption
private Bitmap decodeFile(File f){
try {
//decode image size
BitmapFactory.Options o = new BitmapFactory.Options();
o.inJustDecodeBounds = true;
FileInputStream stream1=new FileInputStream(f);
BitmapFactory.decodeStream(stream1,null,o);
stream1.close();
//Find the correct scale value. It should be the power of 2.
final int REQUIRED_SIZE=256;
int width_tmp=o.outWidth, height_tmp=o.outHeight;
int scale=1;
while(true){
if(width_tmp/2<REQUIRED_SIZE || height_tmp/2<REQUIRED_SIZE)
break;
width_tmp/=2;
height_tmp/=2;
scale*=2;
}
//decode with inSampleSize
BitmapFactory.Options o2 = new BitmapFactory.Options();
o2.inSampleSize=scale;
FileInputStream stream2=new FileInputStream(f);
Bitmap bitmap=BitmapFactory.decodeStream(stream2, null, o2);
stream2.close();
return bitmap;
} catch (FileNotFoundException e) {
}
catch (IOException e) {
e.printStackTrace();
}
return null;
}
//Task for the queue
private class PhotoToLoad
{
public String url;
public ImageView imageView;
public PhotoToLoad(String u, ImageView i){
url=u;
imageView=i;
}
}
class PhotosLoader implements Runnable {
PhotoToLoad photoToLoad;
PhotosLoader(PhotoToLoad photoToLoad){
this.photoToLoad=photoToLoad;
}
@Override
public void run() {
try{
if(imageViewReused(photoToLoad))
return;
Bitmap bmp=getBitmap(photoToLoad.url);
memoryCache.put(photoToLoad.url, bmp);
if(imageViewReused(photoToLoad))
return;
BitmapDisplayer bd=new BitmapDisplayer(bmp, photoToLoad);
handler.post(bd);
}catch(Throwable th){
th.printStackTrace();
}
}
}
boolean imageViewReused(PhotoToLoad photoToLoad){
String tag=imageViews.get(photoToLoad.imageView);
if(tag==null || !tag.equals(photoToLoad.url))
return true;
return false;
}
//Used to display bitmap in the UI thread
class BitmapDisplayer implements Runnable
{
Bitmap bitmap;
PhotoToLoad photoToLoad;
public BitmapDisplayer(Bitmap b, PhotoToLoad p){bitmap=b;photoToLoad=p;}
public void run()
{
if(imageViewReused(photoToLoad))
return;
if(bitmap!=null)
photoToLoad.imageView.setImageBitmap(bitmap);
else
photoToLoad.imageView.setImageResource(stub_id);
}
}
public void clearCache() {
memoryCache.clear();
fileCache.clear();
}
}
答案 0 :(得分：0)
如果你不反对使用图书馆这样做，我在Universal Image Loader取得了很大的成功。这需要解决问题的复杂性，并且很容易设置。有一些问题from a while back与其他一些实现有一些讨论（我不确定它们是否有任何维护）。即使您不使用该库，它们的设计模式也可能是一个有用的起点。