我正在寻找答案半天，但我找不到任何东西，虽然我认为这是一个常见的问题。我的问题：
我有一个ListView，其中包含不同大小（高度）的项目。每个项目都包含ImageView。此ImageView的图像由ImageLoader类在后台加载：
imageLoader.DisplayImage(url, holder.image);
如果我向下滚动ListView一切正常。图像被加载并显示（当然在屏幕/列表的底部）。
但是如果我向上滚动并且图像不再存储在缓存中，那么ImageLoader必须重新加载图像，ListView跳转/项目被移动。我认为这是因为在列表顶部创建了一个新的View，其中ImageView的高度为0dp。如果加载图像并将其设置为ImageView，则ImageView的高度会自动从0dp更改为图像的大小。我认为这会推动ListView。
如果设置了图片，我尝试保存ImageViews的高度，然后将在顶部创建的ImageView的高度设置为已保存的高度。但没有成功..
我不知道你是否能理解我的问题：D我希望如此：）
谢谢，祝你有愉快的一天！
编辑：添加了ImageLoader班级
public class ImageLoader {
MemoryCache memoryCache=new MemoryCache();
FileCache fileCache;
int size;
Context context;
private Map<ImageView, String> imageViews=Collections.synchronizedMap(new WeakHashMap<ImageView, String>());
private HashMap<String, Integer> imagesSizes;
ExecutorService executorService;
Handler handler=new Handler();//handler to display images in UI thread
public ImageLoader(Context context, int size){
fileCache=new FileCache(context);
this.context = context;
executorService=Executors.newFixedThreadPool(5);
this.size = size;
imagesSizes = new HashMap<String, Integer>();
}
final int stub_id=R.color.transparent;
public void DisplayImage(String url, ImageView imageView)
{
imageViews.put(imageView, url);
Bitmap bitmap=memoryCache.get(url);
if(bitmap!=null){
imageView.setImageBitmap(bitmap);
saveImageSize(imageView, url);
}
else
{
queuePhoto(url, imageView);
imageView.setImageResource(stub_id);
setImageSize(imageView, url);
}
}
public void DisplayImage(File file, ImageView imageView)
{
imageViews.put(imageView, file.getAbsolutePath());
Bitmap bitmap=memoryCache.get(file.getAbsolutePath());
if(bitmap!=null){
imageView.setImageBitmap(bitmap);
saveImageSize(imageView, file.getAbsolutePath());
}
else
{
queuePhoto(file, imageView);
imageView.setImageResource(stub_id);
setImageSize(imageView, file.getAbsolutePath());
}
}
private void saveImageSize(ImageView imageView, String url){
int height = imageView.getHeight();
imagesSizes.put(url, height);
System.out.println("IMAGE SIZE: Save: " + url + " " + height );
}
private void setImageSize(ImageView imageView, String url){
if(imageView != null && imagesSizes!=null && imagesSizes.containsKey(url)){
imageView.getLayoutParams().height = imagesSizes.get(url);
imageView.requestLayout();
System.out.println("IMAGE SIZE: Set: " + url + " " + imagesSizes.get(url) );
}
}
private void queuePhoto(String url, ImageView imageView)
{
PhotoToLoad p=new PhotoToLoad(url, imageView);
executorService.submit(new PhotosLoader(p));
}
private void queuePhoto(File file, ImageView imageView)
{
PhotoToLoad p=new PhotoToLoad(file, imageView);
executorService.submit(new PhotosLoader(p));
}
public Bitmap getImage(String url){
return getBitmap(url);
}
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=size;
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 File file;
public String url;
public ImageView imageView;
public PhotoToLoad(String u, ImageView i){
url=u;
imageView=i;
file = null;
}
public PhotoToLoad(File file, ImageView i){
url=file.getAbsolutePath();
imageView=i;
this.file = file;
}
}
class PhotosLoader implements Runnable {
PhotoToLoad photoToLoad;
PhotosLoader(PhotoToLoad photoToLoad){
this.photoToLoad=photoToLoad;
}
@Override
public void run() {
try{
if(imageViewReused(photoToLoad))
return;
Bitmap bmp;
if(photoToLoad.file== null){
bmp=getBitmap(photoToLoad.url);
} else {
bmp=decodeFile(photoToLoad.file);
}
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);
if(photoToLoad.file== null){
setImageSize(photoToLoad.imageView, photoToLoad.url);
} else {
setImageSize(photoToLoad.imageView, photoToLoad.file.getAbsolutePath());
}
}
}
public void clearCache() {
memoryCache.clear();
fileCache.clear();
}
编辑：已添加适配器：
public class LazyNewPostsAdapter extends BaseAdapter implements Constants{
private Activity activity;
private ArrayList<Image> data;
private static LayoutInflater inflater=null;
private ImageLoader imageLoader;
private AsyncHelper helper;
public static final int VIEW_TYPE_LOADING = 0;
public static final int VIEW_TYPE_ACTIVITY = 1;
private int imgposition;
Handler fmHandler = null;
Handler handler = new Handler(){
public void handleMessage(android.os.Message msg) {
switch(msg.what){
case HANDLER_NEW_POST_VOTE_IMAGE:
int position = msg.arg1;
JSONObject json;
try {
json = new JSONObject((String) msg.obj);
int success = json.getInt("success");
if(success == 1){
int i_id = json.getInt("i_id");
int votesUp = json.getInt("votes_up");
int votesDown = json.getInt("votes_down");
data.get(position).setVotesUp(votesUp);
data.get(position).setVotesDown(votesDown);
notifyDataSetChanged();
}
} catch (JSONException e) {
e.printStackTrace();
}
break;
case HANDLER_USER_REPORTED_IMAGE:
JSONObject json2 = Utils.createJSON((String)msg.obj);
System.out.println("REPORT IMAGE " + json2);
if(json2 != null){
try {
int success = json2.getInt("success");
if(success==1){
Toast.makeText(activity, "Image reported!", Toast.LENGTH_LONG).show();
}
} catch (JSONException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
break;
case HANDLER_IMAGE_SIZE_AVAILABLE:
String url = (String) msg.obj;
int height = msg.arg1;
int width = msg.arg2;
int imgPosition = findImageOfCertainURL(url);
System.out.println("GETVIEW HANDLER 1: IMAGE POSITION" + imgPosition);
if(imgPosition != -1){
data.get(imgPosition).setHeight(height);
data.get(imgPosition).setWidth(width);
}
Message copyMsg = new Message();
copyMsg.what = HANDLER_IMAGE_SIZE_AVAILABLE;
copyMsg.arg1 = height;
copyMsg.arg2 = width;
copyMsg.obj = url;
fmHandler.sendMessage(copyMsg);
notifyDataSetChanged();
break;
}
};
};
private int findImageOfCertainURL(String url){
for(int i = 0; i <data.size();i++){
if((URL_FOLDER_IMAGES + data.get(i).getUrl()).equalsIgnoreCase(url)){
return i;
}
}
return -1;
}
public LazyNewPostsAdapter(Activity a, ArrayList<Image> d, Handler fragmentHandler) {
activity = a;
data=d;
inflater = (LayoutInflater)activity.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
helper = new AsyncHelper(activity, handler);
imageLoader=new ImageLoader(activity.getApplicationContext(), 600,handler) ;
fmHandler = fragmentHandler;
}
public void updateData(ArrayList<Image> d){
data = d;
notifyDataSetChanged();
}
public int getCount() {
return data.size()+1;
}
@Override
public int getViewTypeCount() {
return 2;
}
@Override
public int getItemViewType(int position) {
// TODO Auto-generated method stub
return (position >= data.size()) ? VIEW_TYPE_LOADING
: VIEW_TYPE_ACTIVITY;
}
@Override
public boolean isEnabled(int position) {
return getItemViewType(position) == VIEW_TYPE_ACTIVITY;
}
public Object getItem(int position) {
return (getItemViewType(position) == VIEW_TYPE_ACTIVITY) ? data.get(position) : null;
}
public long getItemId(int position) {
return (getItemViewType(position) == VIEW_TYPE_ACTIVITY) ? position
: -1;
}
public View getFooterView(int position, View convertView,
ViewGroup parent) {
// the ListView has reached the last row
TextView tvLastRow = new TextView(activity);
if(AsyncHelper.isDownloadingImages){
tvLastRow.setHint("Requesting new Images..");
} else {
tvLastRow.setHint("Reached the last row.");
}
tvLastRow.setGravity(Gravity.CENTER);
return tvLastRow;
}
private OnClickListener myHotButtonClickListener = new OnClickListener() {
@Override
public void onClick(View v) {
int position = (Integer) v.getTag();
if(ActivityMain.user.isLoggedIn()){
data.get(position).setThisUserVote(1);
helper.vote_image(position, data.get(position).getId(), HOT);
} else {
Toast.makeText(activity, "Login to vote" , Toast.LENGTH_SHORT).show();
}
}
};
private OnClickListener myColdButtonClickListener = new OnClickListener() {
@Override
public void onClick(View v) {
int position = (Integer) v.getTag();
if(ActivityMain.user.isLoggedIn()){
data.get(position).setThisUserVote(2);
helper.vote_image(position, data.get(position).getId(), COLD);
}else {
Toast.makeText(activity, "Login to vote" , Toast.LENGTH_SHORT).show();
}
}
};
private OnClickListener myOptionsButtonClickListener = new OnClickListener() {
@Override
public void onClick(View v) {
final int position = (Integer) v.getTag();
Runnable optionsRunnable = new Runnable() {
@Override
public void run() {
openOptionsDialog(position);
}
};
handler.postDelayed(optionsRunnable, 500);
}
};
private void openOptionsDialog(final int imgposition){
final CharSequence[] items = {"Share", "Save", "Report"};
AlertDialog.Builder builder = new AlertDialog.Builder(activity);
builder.setTitle("Options");
builder.setItems(items, new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog, int item) {
if(item==0){
Utils.shareImage(activity, imageLoader.getImage(URL_FOLDER_IMAGES + data.get(imgposition).getUrl()) , data.get(imgposition).getTitle());
} else if(item==1) {
Utils.saveImage(imageLoader.getImage(URL_FOLDER_IMAGES + data.get(imgposition).getUrl()),activity);
} else if(item==2) {
openReportDialog(imgposition);
}
}
});
AlertDialog alert = builder.create();
alert.show();
}
private void openReportDialog(final int imgposition){
AlertDialog.Builder builder = new AlertDialog.Builder(activity, R.style.AppCompatAlertDialogStyle);
builder.setTitle("Report This Image?");
builder.setPositiveButton("Yes", new DialogInterface.OnClickListener() {
@Override
public void onClick(DialogInterface dialog, int which) {
helper.reportImage(data.get(imgposition).getId());
}
});
builder.setNegativeButton("No", null);
AlertDialog alert = builder.create();
alert.show();
}
public View getView(final int position, View convertView, ViewGroup parent) {
if (getItemViewType(position) == VIEW_TYPE_LOADING) {
// display the last row
return getFooterView(position, convertView, parent);
}
View vi=convertView;
final ViewHolder holder;
final Image img = data.get(position);
boolean isViNull = false;
if(convertView==null){
vi = inflater.inflate(R.layout.item_new_posts, null);
holder = new ViewHolder();
isViNull = true;
holder.title=(BrushTextView)vi.findViewById(R.id.tv_newposts_title);
holder.image=(RatioImageView)vi.findViewById(R.id.iv_newposts_image);
holder.uploader = (BrushTextView) vi.findViewById(R.id.tv_newposts_uploader);
holder.upvotes = (BrushTextView) vi.findViewById(R.id.tv_newposts_upvotes);
holder.downvotes= (BrushTextView) vi.findViewById(R.id.tv_newposts_downvotes);
holder.options=(LinearLayout)vi.findViewById(R.id.ll_newposts_button_options);
holder.iv_hot=(ImageView)vi.findViewById(R.id.iv_newposts_button_upvote);
holder.iv_cold=(ImageView)vi.findViewById(R.id.iv_newposts_button_downvote);
holder.ll_hot=(LinearLayout)vi.findViewById(R.id.ll_newposts_button_upvote);
holder.ll_cold=(LinearLayout)vi.findViewById(R.id.ll_newposts_button_downvote);
vi.setTag(holder);
} else {
holder = (ViewHolder) vi.getTag();
}
if(img.getHeight() != 0 && img.getWidth() != 0){
holder.image.getLayoutParams().height = img.getHeight();
holder.image.getLayoutParams().width = img.getWidth();
holder.image.requestLayout();
}
holder.ll_hot.setTag(position);
holder.ll_hot.setOnClickListener(myHotButtonClickListener);
holder.ll_cold.setTag(position);
holder.ll_cold.setOnClickListener(myColdButtonClickListener);
holder.options.setTag(position);
holder.options.setOnClickListener(myOptionsButtonClickListener);
changeVoteButtonImages(img, holder.iv_hot, holder.iv_cold);
if(img.getTitle()!=null){
holder.title.setVisibility(View.VISIBLE);
holder.title.setText(img.getTitle());
} else {
holder.title.setVisibility(View.GONE);
}
holder.uploader.setText(img.getUploader());
holder.upvotes.setText(img.getVotesUp()+"");
holder.downvotes.setText(img.getVotesDown()+"");
String url = URL_FOLDER_IMAGES + img.getUrl();
System.out.println("GETVIEW NEW POST ADAPTER: height = " + img.getHeight() + " width = " + img.getWidth());
if(isViNull)
System.out.println("GETVIEW CONVERTVIEW: VI: " +vi.getHeight());
imageLoader.DisplayImage(url, holder.image);
return vi;
}
private void changeVoteButtonImages(Image image, ImageView upvote,ImageView downvote){
switch(image.getThisUserVote()){
case 0:
upvote.setImageDrawable(activity.getResources().getDrawable(R.drawable.ic_post_hot_0));
downvote.setImageDrawable(activity.getResources().getDrawable(R.drawable.ic_post_cold_0));
break;
case 1:
downvote.setImageDrawable(activity.getResources().getDrawable(R.drawable.ic_post_cold_0));
upvote.setImageDrawable(activity.getResources().getDrawable(R.drawable.ic_post_hot_1));
break;
case 2:
upvote.setImageDrawable(activity.getResources().getDrawable(R.drawable.ic_post_hot_0));
downvote.setImageDrawable(activity.getResources().getDrawable(R.drawable.ic_post_cold_1));
break;
}
}
static class ViewHolder {
public BrushTextView title, uploader, upvotes, downvotes;
public ImageView iv_hot,iv_cold;
public LinearLayout options, ll_hot,ll_cold;
public RatioImageView image;
}
}
以下是Fragment，其中包含ListView
public class Fragment_New_Posts extends Fragment implements Constants, OnRefreshListener{
private static final String ARG_SECTION_NUMBER = "section_number";
private ListView list;
private LazyNewPostsAdapter adapter;
private Images images;
private ArrayList<Image> imagesList;
private SharedPreferences prefs;
private Editor editor;
private int visible_i_id;
private SwipeRefreshLayout swipeLayout;
private int option_image_filter;
private AsyncHelper helper;
private boolean onRefreshFired = false;
private Parcelable state;
public static Fragment_New_Posts newInstance(int sectionNumber) {
Fragment_New_Posts fragment = new Fragment_New_Posts();
Bundle args = new Bundle();
args.putInt(ARG_SECTION_NUMBER, sectionNumber);
fragment.setArguments(args);
return fragment;
}
public static Fragment_New_Posts newInstance(int sectionNumber, Images imgs) {
Fragment_New_Posts fragment = new Fragment_New_Posts(imgs);
Bundle args = new Bundle();
args.putInt(ARG_SECTION_NUMBER, sectionNumber);
fragment.setArguments(args);
return fragment;
}
public void updateImages(Images images, boolean createNew, boolean loadOldImages){
int i_id_position = 0;
this.images = images;
if(!images.hasErrorOccured){
if(this.imagesList == null || createNew || onRefreshFired){
this.imagesList = images.getListOfImages();
} else {
this.imagesList.addAll(images.getListOfImages());
}
}
if(loadOldImages){
i_id_position = this.images.getIDPosition(visible_i_id);
}
if(onRefreshFired){
swipeLayout.setRefreshing(false);
onRefreshFired = false;
}
synchronized (adapter) {
adapter.updateData(this.imagesList);
if(list!=null && createNew){
if(loadOldImages){
list.setSelection(i_id_position);
} else {
list.setSelection(0);
}
}
}
}
private Handler handler = new Handler(){
public void handleMessage(android.os.Message msg) {
switch(msg.what){
case HANDLER_MAIN_IMAGE_UPDATE:
String imagesString = (String) msg.obj;
Images imgs = new Images(imagesString);
updateImages(imgs, false, false);
if(imgs.hasErrorOccured){
Toast.makeText(getActivity(), "Can\'t get new Images", Toast.LENGTH_SHORT).show();
}
break;
case HANDLER_IMAGE_SIZE_AVAILABLE:
String url = (String) msg.obj;
int height = msg.arg1;
int width = msg.arg2;
int imgPosition = findImageOfCertainURL(url);
System.out.println("GETVIEW HANDLER 2: IMAGE POSITION" + imgPosition);
if(imgPosition != -1){
imagesList.get(imgPosition).setHeight(height);
imagesList.get(imgPosition).setWidth(width);
}
break;
}
};
};
private int findImageOfCertainURL(String url){
for(int i = 0; i <imagesList.size();i++){
if((URL_FOLDER_IMAGES + imagesList.get(i).getUrl()).equalsIgnoreCase(url)){
return i;
}
}
return -1;
}
public Fragment_New_Posts() {
}
public Fragment_New_Posts(Images imgs) {
this.images = imgs;
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
System.out.println("NEW POST FRAGMENT ONCREATE");
View rootView = inflater.inflate(R.layout.fragment_new_posts, container, false);
prefs = getActivity().getSharedPreferences(PREF_WOODU, getActivity().MODE_PRIVATE);
editor = prefs.edit();
if(prefs!=null){
visible_i_id = prefs.getInt(PREF_NEW_POSTS_VISIBLE_I_ID, 0);
option_image_filter = prefs.getInt(PHP_TAG_IMAGE_FILTER, 0);
}
swipeLayout = (SwipeRefreshLayout) rootView.findViewById(R.id.swipe_container);
swipeLayout.setColorSchemeColors(R.color.red_hot);
swipeLayout.setOnRefreshListener(this);
helper = new AsyncHelper(getActivity(), handler);
imagesList = new ArrayList<Image>();
if(images != null){
imagesList = images.getListOfImages();
System.out.println("SAVE IMAGES: load: imgsList " + imagesList);
}
list = (ListView) rootView.findViewById(R.id.lv_new_posts);
adapter = new LazyNewPostsAdapter(getActivity(), imagesList, handler);
list.setAdapter(adapter);
list.setOnScrollListener(new EndlessScrollListener() {
@Override
public void onLoadMore(int page, int totalItemsCount) {
if(imagesList!=null && imagesList.size()!=0){
helper.getImageUpdate(imagesList.get(imagesList.size()-1).getId(), option_image_filter);
}
}
});
if(images != null){
updateImages(images, true, true);
}
return rootView;
}
@Override
public void onPause() {
int lastVisposition = list.getLastVisiblePosition();
if(lastVisposition>=0 && lastVisposition < this.imagesList.size()){
visible_i_id = this.imagesList.get(list.getFirstVisiblePosition()).getId();
editor.putInt(PREF_NEW_POSTS_VISIBLE_I_ID, visible_i_id);
editor.commit();
}
super.onPause();
}
@Override
public void onResume() {
super.onResume();
}
@Override
public void onDestroy() {
if(images != null){
editor.putString(PREF_NEW_POSTS_CURRENT_IMAGES, Utils.createJSONStringFromImageArrayList(imagesList, editor));
editor.commit();
}
super.onDestroy();
}
@Override
public void onRefresh() {
onRefreshFired = true;
if(prefs!=null){
option_image_filter = prefs.getInt(PHP_TAG_IMAGE_FILTER, 0);
}
helper.getImageUpdate(0, option_image_filter);
}
}
现在这里有很多信息和代码。我希望这不会吓到任何人帮忙：D
谢谢！
答案 0 :(得分：4)
拜托，请，请不要“重新发明轮子”，并使用任何lib来进行图像加载，缓存等，如Picasso，Fresco，Glide等....
答案 1 :(得分：2)
我可能已经解决了问题..最后..我在getView中设置ImageView高度的想法并不是那么糟糕..问题是：
我的ImageView被包装在XML中的CardView内。所以我需要更改CardView的高度而不是ImageView：）
答案 2 :(得分：1)
WeakHashMap ...您正在使用弱引用。哪个是对的。不再使用时删除对象。所以，只需将其更改为HashMap，你应该做得很好。