在过去的几天里，我一直在为这个问题而苦苦挣扎。我已经尝试了堆栈溢出时可用的所有方法，但我无法解决这个问题。
仅当我的第一个项目没有有效的 url 并且仅针对第一个元素时才会出现此错误。向下滚动后，加载了正确的图像。
基本思想是我放置一个临时图像，该图像将替换为从 JSON 加载的图像。如果没有 url（或无效），则应根据我正在显示的动物的类型显示特定的默认值（如果是狗将显示狗图像，如果是猫将显示猫图像，依此类推）。
这是我使用的 ImageLoader 类中的代码：
package ro.nextlogic.petsplus.utils;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.net.HttpURLConnection;
import java.net.URL;
import java.util.Collections;
import java.util.Map;
import java.util.WeakHashMap;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import ro.nextlogic.petsplus.R;
import android.app.Activity;
import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.util.Log;
import android.widget.ImageView;
public class ImageLoader {
static MemoryCache memoryCache=new MemoryCache();
static FileCache fileCache;
private Map<ImageView, String> imageViews=Collections.synchronizedMap(new WeakHashMap<ImageView, String>());
ExecutorService executorService;
/**
* The maximum number of threads used when loading images.
*/
private static final int MAX_THREADS = 5;
private Context context;
private volatile static ImageLoader instance;
/** Returns singleton class instance */
public static ImageLoader getInstance(Context context) {
if (instance == null) {
synchronized (ImageLoader.class) {
if (instance == null) {
instance = new ImageLoader(context);
}
}
}
return instance;
}
private ImageLoader(Context context) {
this.context = context;
fileCache=new FileCache(context);
executorService = Executors.newFixedThreadPool(MAX_THREADS);
}
final int stub_id = R.drawable.default_other;
public void displayImage(String url, ImageView imageView, final int REQUIRED_SIZE) {
if (url == null) {
return;
}
Log.i("BITMAP", "imageView = " + imageView + "\nurl = " + url);
imageViews.put(imageView, url);
Bitmap bitmap=memoryCache.get(url);
if (bitmap!=null && !bitmap.isRecycled() ) {
imageView.setImageBitmap(bitmap);
} else {
queuePhoto(url, imageView, REQUIRED_SIZE);
imageView.setImageResource(stub_id);
}
}
private void queuePhoto(String url, ImageView imageView, final int REQUIRED_SIZE) {
PhotoToLoad p=new PhotoToLoad(url, imageView, REQUIRED_SIZE);
executorService.submit(new PhotosLoader(p));
}
public static Bitmap getBitmap(final String url, final int REQUIRED_SIZE) {
File f = fileCache.getFile(url);
//from SD cache
Bitmap b = decodeFile(f, REQUIRED_SIZE);
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();
bitmap = decodeFile(f, REQUIRED_SIZE);
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 static Bitmap decodeFile(final File f, final int REQUIRED_SIZE) {
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();
// The new size we want to scale to
// final int REQUIRED_SIZE=70; // 70 is best for Thumbnail
// Get the width and height of the image
int width_tmp=o.outWidth, height_tmp=o.outHeight;
// Find the correct scale value. It should be the power of 2.
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 e1) {
// Log.e("IMAGELOADER", "FileNotFoundException: ", e1);
} catch (IOException e2) {
Log.e("IMAGELOADER", "IOException: ", e2);
}
return null;
}
//Task for the queue
private class PhotoToLoad {
public final String url;
public final ImageView imageView;
public final int REQUIRED_SIZE;
public PhotoToLoad(final String u, final ImageView i, final int rq){
url=u;
imageView=i;
REQUIRED_SIZE = rq;
}
}
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, photoToLoad.REQUIRED_SIZE);
memoryCache.put(photoToLoad.url, bmp);
if(imageViewReused(photoToLoad))
return;
BitmapDisplayer bd=new BitmapDisplayer(bmp, photoToLoad);
Activity a=(Activity)photoToLoad.imageView.getContext();
a.runOnUiThread(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)
Utils.imageViewAnimatedChange(context, photoToLoad.imageView, bitmap);
// photoToLoad.imageView.setImageBitmap(bitmap);
}
}
public void clearCache() {
memoryCache.clear();
fileCache.clear();
}
}
这就是我所说的：
@Override
public View getView(int position, View convertView, ViewGroup parent) {
View rowView = convertView;
final ViewHolder holder;
if (convertView == null) {
rowView = inflator.inflate(R.layout.shelter_animal_rowlayout, parent, false);
holder = new ViewHolder();
holder.animalImg = (ImageView) rowView.findViewById(R.id.shelter_animal_image);
holder.animalName = (TextView) rowView.findViewById(R.id.shelter_animal_name);
holder.animalDescription = (TextView) rowView.findViewById(R.id.shelter_animal_description);
rowView.setTag(holder);
} else {
holder = ((ViewHolder) rowView.getTag());
}
AnimalItem animalItem = filteredModelItemsArray.get(position);
if (animalItem != null) {
// Display the animal name, set "Unknown" if not available
if (!TextUtils.isEmpty(animalItem.name) && // Not empty
!animalItem.name.contains("Unknown")) { // Not Unknown
holder.animalName.setText(animalItem.name);
} else {
holder.animalName.setText(R.string.shelter_animal_name);
}
// Display the animal description, set "Unknown" if not available
if (!TextUtils.isEmpty(animalItem.description) && // Not empty
!animalItem.description.contains("Unknown")) { // Not Unknown
holder.animalDescription.setText(Html.fromHtml(animalItem.description));
} else {
holder.animalDescription.setText(R.string.shelter_animal_description);
}
// Display the animal image
if (animalItem.photo != null) {
imageLoader.displayImage(animalItem.photo, holder.animalImg, 70);
} else if (animalItem.animal.contains("Dog")) {
holder.animalImg.setImageResource(R.drawable.default_dog);
} else if (animalItem.animal.contains("Cat")) {
holder.animalImg.setImageResource(R.drawable.default_cat);
} else {
holder.animalImg.setImageResource(android.R.drawable.ic_menu_help);
}
} else {
Toast.makeText(context, "NO animals retrieved from server!", Toast.LENGTH_LONG).show();
}
return rowView;
}
animalItem.photo是来自 JSON 的 url
animalItem.animal也是从 JSON 获得的动物类型
我应该提到文本显示正常......只有图像是错误的，并且仅适用于第一个元素（当照片不可用时）。
如果有人能指出我正确的方向或告诉我做错了什么，将不胜感激。
编辑： 我想我通过不再使用 WeakHashMap 并在 Map 中保存每个 ImageView 的 hashCode 来解决这个问题。所以这就是我改变的：
private Map<ImageView, String> imageViews=Collections.synchronizedMap(new WeakHashMap<ImageView, String>());
进入
private Map<Integer, String> imageViews=Collections.synchronizedMap(new HashMap<Integer, String>());
并用于保存和获取值：
imageViews.put(imageView, url);
进入
imageViews.put(imageView.hashCode(), url);
和
imageViews.get(photoToLoad.imageView);
进入
imageViews.get(photoToLoad.imageView.hashCode());
解决方案： 我通过添加取消图像加载的方法解决了这个问题而不影响性能：
这是方法（在 ImageLoader 中声明）：
public void cancelDisplayTaskFor(ImageView imageView) {
imageViews.remove(imageView);
}
并将在我设置图像的自定义 ArrayAdapter 中调用此方法：
// Display the animal image
if (animalItem.photo != null) {
imageLoader.displayImage(animalItem.photo, holder.animalImg, 70);
} else if (animalItem.animal.contains("Dog")) {
imageLoader.cancelDisplayTaskFor(holder.animalImg);
holder.animalImg.setImageResource(R.drawable.default_dog);
} else if (animalItem.animal.contains("Cat")) {
imageLoader.cancelDisplayTaskFor(holder.animalImg);
holder.animalImg.setImageResource(R.drawable.default_cat);
} else {
imageLoader.cancelDisplayTaskFor(holder.animalImg);
holder.animalImg.setImageResource(android.R.drawable.ic_menu_help);
}
希望这对其他人有帮助:)