我正在开发一个应用程序，我必须从互联网上延迟加载图像并将它们放在gridview中。 问题是，当我加载这些图像时，它们会在此gridview的滚动中混合。 例如，应该出现在第一个位置的图片出现在第3个位置，依此类推。 有人可以帮帮我吗？
这是我的主要活动代码：
import android.app.Activity;
import android.os.Bundle;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.GridView;
import android.widget.Toast;
public class MainActivityLoading extends Activity {
GridView grid;
LazyImageLoadAdapter adapter;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main_activity_loading);
grid=(GridView)findViewById(R.id.gridView1);
// Create custom adapter for listview
adapter=new LazyImageLoadAdapter(getApplicationContext(), this, mStrings);
grid.setAdapter(adapter);
Button b=(Button)findViewById(R.id.button1);
b.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View arg0) {
//Refresh cache directory downloaded images
adapter.imageLoader.clearCache();
adapter.notifyDataSetChanged();
}
});;
}
@Override
public void onDestroy()
{
// Remove adapter refference from list
grid.setAdapter(null);
super.onDestroy();
}
public void onItemClick(int mPosition)
{
String tempValues = mStrings[mPosition];
Toast.makeText(MainActivityLoading.this,
"Image URL : "+tempValues,
Toast.LENGTH_LONG).show();
}
// Image urls used in LazyImageLoadAdapter.java file
private String[] mStrings={
"http://icons.iconarchive.com/icons/visualpharm/icons8-metro-style/512/Emoticons-Sad-icon.png",
"http://icons.iconarchive.com/icons/visualpharm/icons8-metro-style/512/Emoticons-Happy-icon.png",
"http://icons.iconarchive.com/icons/visualpharm/icons8-metro-style/512/Emoticons-Crying-icon.png",
"http://icons.iconarchive.com/icons/visualpharm/icons8-metro-style/512/Emoticons-Cool-icon.png",
"http://icons.iconarchive.com/icons/visualpharm/icons8-metro-style/512/Emoticons-In-love-icon.png",
"http://icons.iconarchive.com/icons/visualpharm/icons8-metro-style/512/Emoticons-Lol-icon.png",
"http://icons.iconarchive.com/icons/visualpharm/icons8-metro-style/512/Emoticons-Surprised-icon.png",
"http://icons.iconarchive.com/icons/visualpharm/icons8-metro-style/512/Emoticons-Tongue-icon.png",
"http://icons.iconarchive.com/icons/visualpharm/icons8-metro-style/512/Emoticons-Wink-icon.png",
"http://icons.iconarchive.com/icons/visualpharm/icons8-metro-style/512/Emoticons-Sad-icon.png",
"http://icons.iconarchive.com/icons/visualpharm/icons8-metro-style/512/Emoticons-Happy-icon.png",
"http://icons.iconarchive.com/icons/visualpharm/icons8-metro-style/512/Emoticons-Crying-icon.png",
"http://icons.iconarchive.com/icons/visualpharm/icons8-metro-style/512/Emoticons-Cool-icon.png",
"http://icons.iconarchive.com/icons/visualpharm/icons8-metro-style/512/Emoticons-In-love-icon.png",
"http://icons.iconarchive.com/icons/visualpharm/icons8-metro-style/512/Emoticons-Lol-icon.png",
"http://icons.iconarchive.com/icons/visualpharm/icons8-metro-style/512/Emoticons-Surprised-icon.png",
"http://icons.iconarchive.com/icons/visualpharm/icons8-metro-style/512/Emoticons-Tongue-icon.png",
"http://icons.iconarchive.com/icons/visualpharm/icons8-metro-style/512/Emoticons-Wink-icon.png",
"http://icons.iconarchive.com/icons/visualpharm/icons8-metro-style/512/Emoticons-Sad-icon.png",
"http://icons.iconarchive.com/icons/visualpharm/icons8-metro-style/512/Emoticons-Happy-icon.png",
"http://icons.iconarchive.com/icons/visualpharm/icons8-metro-style/512/Emoticons-Crying-icon.png",
"http://icons.iconarchive.com/icons/visualpharm/icons8-metro-style/512/Emoticons-Cool-icon.png",
"http://icons.iconarchive.com/icons/visualpharm/icons8-metro-style/512/Emoticons-In-love-icon.png",
"http://icons.iconarchive.com/icons/visualpharm/icons8-metro-style/512/Emoticons-Lol-icon.png",
"http://icons.iconarchive.com/icons/visualpharm/icons8-metro-style/512/Emoticons-Surprised-icon.png",
"http://icons.iconarchive.com/icons/visualpharm/icons8-metro-style/512/Emoticons-Tongue-icon.png",
"http://icons.iconarchive.com/icons/visualpharm/icons8-metro-style/512/Emoticons-Wink-icon.png"
};
}
这是我的LazyImageLoadAdapter类代码：
import android.app.Activity;
import android.content.Context;
import android.view.LayoutInflater;
import android.view.View;
import android.view.View.OnClickListener;
import android.view.ViewGroup;
import android.widget.BaseAdapter;
import android.widget.ImageView;
public class LazyImageLoadAdapter extends BaseAdapter implements OnClickListener{
private Activity activity;
private String[] mStrings;
private Context mContext;
private static LayoutInflater inflater=null;
public ImageLoader imageLoader;
public LazyImageLoadAdapter(Context context, Activity a, String[] d) {
activity = a;
mStrings=d;
mContext = context;
inflater = (LayoutInflater)activity.
getSystemService(Context.LAYOUT_INFLATER_SERVICE);
imageLoader = new ImageLoader(activity.getApplicationContext());
}
public int getCount() {
return mStrings.length;
}
public Object getItem(int position) {
return position;
}
public long getItemId(int position) {
return position;
}
public View getView(int position, View convertView, ViewGroup parent)
{
View grid;
LayoutInflater inflater = (LayoutInflater) mContext.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
if (convertView == null)
{
grid = new View(mContext);
grid = inflater.inflate(R.layout.listview_row, null);
ImageView imageView = (ImageView)grid.findViewById(R.id.image);
imageLoader.DisplayImage(mStrings[position], imageView);
} else {
grid = (View) convertView;
}
grid.setOnClickListener(new OnItemClickListener(position));
return grid;
}
@Override
public void onClick(View arg0) {
}
private class OnItemClickListener implements OnClickListener{
private int mPosition;
OnItemClickListener(int position){
mPosition = position;
}
@Override
public void onClick(View arg0) {
MainActivityLoading sct = (MainActivityLoading)activity;
sct.onItemClick(mPosition);
}
}
这是我的ImageLoader类代码：
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 android.os.Handler;
import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.widget.ImageView;
public class ImageLoader {
// Initialize MemoryCache
MemoryCache memoryCache = new MemoryCache();
FileCache fileCache;
//Create Map (collection) to store image and image url in key value pair
private Map<ImageView, String> imageViews = Collections.synchronizedMap(
new WeakHashMap<ImageView, String>());
ExecutorService executorService;
//handler to display images in UI thread
Handler handler = new Handler();
public ImageLoader(Context context){
fileCache = new FileCache(context);
// Creates a thread pool that reuses a fixed number of
// threads operating off a shared unbounded queue.
executorService=Executors.newFixedThreadPool(5);
}
// default image shown in list (Before online image download)
final int stub_id=R.drawable.ic_launcher;
public void DisplayImage(String url, ImageView imageView)
{
//Store image and url in Map
imageViews.put(imageView, url);
//Check image is stored in MemoryCache Map or not (see MemoryCache.java)
Bitmap bitmap = memoryCache.get(url);
if(bitmap!=null){
// if image is stored in MemoryCache Map then
// Show image in listview row
imageView.setImageBitmap(bitmap);
}
else
{
//queue Photo to download from url
queuePhoto(url, imageView);
//Before downloading image show default image
imageView.setImageResource(stub_id);
}
}
private void queuePhoto(String url, ImageView imageView)
{
// Store image and url in PhotoToLoad object
PhotoToLoad p = new PhotoToLoad(url, imageView);
// pass PhotoToLoad object to PhotosLoader runnable class
// and submit PhotosLoader runnable to executers to run runnable
// Submits a PhotosLoader runnable task for execution
executorService.submit(new PhotosLoader(p));
}
//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{
//Check if image already downloaded
if(imageViewReused(photoToLoad))
return;
// download image from web url
Bitmap bmp = getBitmap(photoToLoad.url);
// set image data in Memory Cache
memoryCache.put(photoToLoad.url, bmp);
if(imageViewReused(photoToLoad))
return;
// Get bitmap to display
BitmapDisplayer bd=new BitmapDisplayer(bmp, photoToLoad);
// Causes the Runnable bd (BitmapDisplayer) to be added to the message queue.
// The runnable will be run on the thread to which this handler is attached.
// BitmapDisplayer run method will call
handler.post(bd);
}catch(Throwable th){
th.printStackTrace();
}
}
}
private Bitmap getBitmap(String url)
{
File f=fileCache.getFile(url);
//from SD cache
//CHECK : if trying to decode file which not exist in cache return null
Bitmap b = decodeFile(f);
if(b!=null)
return b;
// Download image file 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();
// Constructs a new FileOutputStream that writes to file
// if file not exist then it will create file
OutputStream os = new FileOutputStream(f);
// See Utils class CopyStream method
// It will each pixel from input stream and
// write pixels to output stream (file)
Utils.CopyStream(is, os);
os.close();
conn.disconnect();
//Now file created and going to resize file with defined height
// Decodes image and scales it to reduce memory consumption
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.
// Set width/height of recreated image
final int REQUIRED_SIZE=85;
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 current scale values
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;
}
boolean imageViewReused(PhotoToLoad photoToLoad){
String tag=imageViews.get(photoToLoad.imageView);
//Check url is already exist in imageViews MAP
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;
// Show bitmap on UI
if(bitmap!=null)
photoToLoad.imageView.setImageBitmap(bitmap);
else
photoToLoad.imageView.setImageResource(stub_id);
}
}
public void clearCache() {
//Clear cache directory downloaded images and stored data in maps
memoryCache.clear();
fileCache.clear();
}
}
这是我的MemoryCache类代码：
import java.util.Collections;
import java.util.Iterator;
import java.util.LinkedHashMap;
import java.util.Map;
import java.util.Map.Entry;
import android.graphics.Bitmap;
import android.util.Log;
public class MemoryCache {
private static final String TAG = "MemoryCache";
//Last argument true for LRU ordering
private Map<String, Bitmap> cache = Collections.synchronizedMap(
new LinkedHashMap<String, Bitmap>(10,1.5f,true));
//current allocated size
private long size=0;
//max memory cache folder used to download images in bytes
private long limit=1000000;
public MemoryCache(){
//use 25% of available heap size
setLimit(Runtime.getRuntime().maxMemory()/4);
}
public void setLimit(long new_limit){
limit=new_limit;
Log.i(TAG, "MemoryCache will use up to "+limit/1024./1024.+"MB");
}
public Bitmap get(String id){
try{
if(!cache.containsKey(id))
return null;
return cache.get(id);
}catch(NullPointerException ex){
ex.printStackTrace();
return null;
}
}
public void put(String id, Bitmap bitmap){
try{
if(cache.containsKey(id))
size-=getSizeInBytes(cache.get(id));
cache.put(id, bitmap);
size+=getSizeInBytes(bitmap);
checkSize();
}catch(Throwable th){
th.printStackTrace();
}
}
private void checkSize() {
Log.i(TAG, "cache size="+size+" length="+cache.size());
if(size>limit){
//least recently accessed item will be the first one iterated
Iterator<Entry<String, Bitmap>> iter=cache.entrySet().iterator();
while(iter.hasNext()){
Entry<String, Bitmap> entry=iter.next();
size-=getSizeInBytes(entry.getValue());
iter.remove();
if(size<=limit)
break;
}
Log.i(TAG, "Clean cache. New size "+cache.size());
}
}
public void clear() {
try{
// Clear cache
cache.clear();
size=0;
}catch(NullPointerException ex){
ex.printStackTrace();
}
}
long getSizeInBytes(Bitmap bitmap) {
if(bitmap==null)
return 0;
return bitmap.getRowBytes() * bitmap.getHeight();
}
}
这是我的FileCache类代码：
import java.io.File;
import android.content.Context;
public class FileCache {
private File cacheDir;
public FileCache(Context context){
//Find the dir at SDCARD to save cached images
if (android.os.Environment.getExternalStorageState().equals(
android.os.Environment.MEDIA_MOUNTED))
{
//if SDCARD is mounted (SDCARD is present on device and mounted)
cacheDir = new File(
android.os.Environment.getExternalStorageDirectory(),"LazyList");
}
else
{
// if checking on simulator the create cache dir in your application context
cacheDir=context.getCacheDir();
}
if(!cacheDir.exists()){
// create cache dir in your application context
cacheDir.mkdirs();
}
}
public File getFile(String url){
//Identify images by hashcode or encode by URLEncoder.encode.
String filename=String.valueOf(url.hashCode());
File f = new File(cacheDir, filename);
return f;
}
public void clear(){
// list all files inside cache directory
File[] files=cacheDir.listFiles();
if(files==null)
return;
//delete all cache directory files
for(File f:files)
f.delete();
}
}
这是我的Utils类代码：
import java.io.InputStream;
import java.io.OutputStream;
public class Utils {
public static void CopyStream(InputStream is, OutputStream os)
{
final int buffer_size=1024;
try
{
byte[] bytes=new byte[buffer_size];
for(;;)
{
//Read byte from input stream
int count=is.read(bytes, 0, buffer_size);
if(count==-1)
break;
//Write byte from output stream
os.write(bytes, 0, count);
}
}
catch(Exception ex){}
}
}
非常感谢。
答案 0 :(得分：0)
你为什么要自己做所有这些艰苦的工作。 Android sdk已经有了用于位图缓存和工作线程进程的专用库。 它将为您节省大量精力并使代码更清晰
http://developer.android.com/training/displaying-bitmaps/cache-bitmap.html http://developer.android.com/reference/android/os/AsyncTask.html http://developer.android.com/reference/android/graphics/BitmapFactory.html#decodeStream(java.io.InputStream)
就个人而言，这是我最喜欢的懒人图像加载器，它在低分辨率和高分辨率图像上都能很好地工作 https://github.com/nostra13/Android-Universal-Image-Loader