在Android中使用ImageLoader类调整ListView适配器 [英] Adapting ListView adapter with an ImageLoader Class in Android
问题描述
我有一个实现ImageThreadLoader类的自定义ListView适配器.不幸的是，该类没有启用缓存选项-从网络下载图像并将其保存为缓存.
I have a custom ListView adapter which implements an ImageThreadLoader class. Unfortunately, the class doesn't enable a cache option-download the images from the web and save them as cache.
然后，我发现这个LazyList项目确实非常有用，其行为与ImageThreadLoader类非常相似，但是能够将图像保存为缓存.因此，我想将其ImageLoader类实现为当前的自定义ListView适配器.
And then I found this LazyList project really useful, it behaves quite the same like my ImageThreadLoader class but it's able to save the images as cache. So, I want to implement its ImageLoader class to my current custom ListView adapter.
不幸的是，我的代码和惰性列表的结构完全不同，导致我的尝试有些冲突.例如，LazyList使用字符串数组作为图像URL，另一方面，我使用JSON作为图像URL的源.
Unfortunately the structure of my codes and the Lazylist's is quite different, resulting some conflicts on my attempts. For example, the LazyList use array of strings for the image URL, in the other hand I use JSON as the source of image URL.
这就是为什么我需要帮助来使ListView适配器适应此ImageLoader类的原因.
That's why I need help to adapt my ListView adapter to this ImageLoader class.
以下是代码:
ImageLoader类:
public class ImageLoader {
//the simplest in-memory cache implementation. This should be replaced with something like SoftReference or BitmapOptions.inPurgeable(since 1.6)
private HashMap<String, Bitmap> cache=new HashMap<String, Bitmap>();
private File cacheDir;
public ImageLoader(Context context){
//Make the background thead low priority. This way it will not affect the UI performance
photoLoaderThread.setPriority(Thread.NORM_PRIORITY-1);
//Find the dir to save cached images
if (android.os.Environment.getExternalStorageState().equals(android.os.Environment.MEDIA_MOUNTED))
cacheDir=new File(android.os.Environment.getExternalStorageDirectory(),"Android/data/LazyList");
else
cacheDir=context.getCacheDir();
if(!cacheDir.exists())
cacheDir.mkdirs();
}
final int stub_id=R.drawable.stub;
public void DisplayImage(String url, Activity activity, ImageView imageView)
{
if(cache.containsKey(url))
imageView.setImageBitmap(cache.get(url));
else
{
queuePhoto(url, activity, imageView);
imageView.setImageResource(stub_id);
}
}
private void queuePhoto(String url, Activity activity, ImageView imageView)
{
//This ImageView may be used for other images before. So there may be some old tasks in the queue. We need to discard them.
photosQueue.Clean(imageView);
PhotoToLoad p=new PhotoToLoad(url, imageView);
synchronized(photosQueue.photosToLoad){
photosQueue.photosToLoad.push(p);
photosQueue.photosToLoad.notifyAll();
}
//start thread if it's not started yet
if(photoLoaderThread.getState()==Thread.State.NEW)
photoLoaderThread.start();
}
private Bitmap getBitmap(String url)
{
//I identify images by hashcode. Not a perfect solution, good for the demo.
String filename=String.valueOf(url.hashCode());
File f=new File(cacheDir, filename);
//from SD cache
Bitmap b = decodeFile(f);
if(b!=null)
return b;
//from web
try {
Bitmap bitmap=null;
InputStream is=new URL(url).openStream();
OutputStream os = new FileOutputStream(f);
Utils.CopyStream(is, os);
os.close();
bitmap = decodeFile(f);
return bitmap;
} catch (Exception ex){
ex.printStackTrace();
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;
BitmapFactory.decodeStream(new FileInputStream(f),null,o);
//Find the correct scale value. It should be the power of 2.
final int REQUIRED_SIZE=70;
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;
return BitmapFactory.decodeStream(new FileInputStream(f), null, o2);
} catch (FileNotFoundException e) {}
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;
}
}
PhotosQueue photosQueue=new PhotosQueue();
public void stopThread()
{
photoLoaderThread.interrupt();
}
//stores list of photos to download
class PhotosQueue
{
private Stack<PhotoToLoad> photosToLoad=new Stack<PhotoToLoad>();
//removes all instances of this ImageView
public void Clean(ImageView image)
{
for(int j=0 ;j<photosToLoad.size();){
if(photosToLoad.get(j).imageView==image)
photosToLoad.remove(j);
else
++j;
}
}
}
class PhotosLoader extends Thread {
public void run() {
try {
while(true)
{
//thread waits until there are any images to load in the queue
if(photosQueue.photosToLoad.size()==0)
synchronized(photosQueue.photosToLoad){
photosQueue.photosToLoad.wait();
}
if(photosQueue.photosToLoad.size()!=0)
{
PhotoToLoad photoToLoad;
synchronized(photosQueue.photosToLoad){
photoToLoad=photosQueue.photosToLoad.pop();
}
Bitmap bmp=getBitmap(photoToLoad.url);
cache.put(photoToLoad.url, bmp);
Object tag=photoToLoad.imageView.getTag();
if(tag!=null && ((String)tag).equals(photoToLoad.url)){
BitmapDisplayer bd=new BitmapDisplayer(bmp, photoToLoad.imageView);
Activity a=(Activity)photoToLoad.imageView.getContext();
a.runOnUiThread(bd);
}
}
if(Thread.interrupted())
break;
}
} catch (InterruptedException e) {
//allow thread to exit
}
}
}
PhotosLoader photoLoaderThread=new PhotosLoader();
//Used to display bitmap in the UI thread
class BitmapDisplayer implements Runnable
{
Bitmap bitmap;
ImageView imageView;
public BitmapDisplayer(Bitmap b, ImageView i){bitmap=b;imageView=i;}
public void run()
{
if(bitmap!=null)
imageView.setImageBitmap(bitmap);
else
imageView.setImageResource(stub_id);
}
}
public void clearCache() {
//clear memory cache
cache.clear();
//clear SD cache
File[] files=cacheDir.listFiles();
for(File f:files)
f.delete();
}
}
LazyList项目中的自定义列表视图适配器:
public class LazyAdapter extends BaseAdapter {
private Activity activity;
private String[] data;
private static LayoutInflater inflater=null;
public ImageLoader imageLoader;
public LazyAdapter(Activity a, String[] d) {
activity = a;
data=d;
inflater = (LayoutInflater)activity.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
imageLoader=new ImageLoader(activity.getApplicationContext());
}
public int getCount() {
return data.length;
}
public Object getItem(int position) {
return position;
}
public long getItemId(int position) {
return position;
}
public static class ViewHolder{
public TextView text;
public ImageView image;
}
public View getView(int position, View convertView, ViewGroup parent) {
View vi=convertView;
ViewHolder holder;
if(convertView==null){
vi = inflater.inflate(R.layout.item, null);
holder=new ViewHolder();
holder.text=(TextView)vi.findViewById(R.id.text);;
holder.image=(ImageView)vi.findViewById(R.id.image);
vi.setTag(holder);
}
else
holder=(ViewHolder)vi.getTag();
holder.text.setText("item "+position);
holder.image.setTag(data[position]);
imageLoader.DisplayImage(data[position], activity, holder.image);
return vi;
}
}
这是我的自定义ListView适配器: ProjectAdapter类
public class ProjectAdapter extends ArrayAdapter<Project> {
int resource;
String response;
Context context;
private final static String TAG = "MediaItemAdapter";
private ImageThreadLoader imageLoader = new ImageThreadLoader();
//Initialize adapter
public ProjectAdapter(Context context, int resource, List<Project> items) {
super(context, resource, items);
this.resource=resource;
}
@Override
public View getView(int position, View convertView, ViewGroup parent)
{
TextView textTitle;
final ImageView image;
Project pro = getItem(position);
LinearLayout projectView;
//Inflate the view
if(convertView==null)
{
projectView = new LinearLayout(getContext());
String inflater = Context.LAYOUT_INFLATER_SERVICE;
LayoutInflater vi;
vi = (LayoutInflater)getContext().getSystemService(inflater);
vi.inflate(resource, projectView, true);
}
else
{
projectView = (LinearLayout) convertView;
}
try {
textTitle = (TextView)projectView.findViewById(R.id.txt_title);
image = (ImageView)projectView.findViewById(R.id.image);
} catch( ClassCastException e ) {
Log.e(TAG, "Your layout must provide an image and a text view with ID's icon and text.", e);
throw e;
}
Bitmap cachedImage = null;
try {
cachedImage = imageLoader.loadImage(pro.smallImageUrl, new ImageLoadedListener() {
public void imageLoaded(Bitmap imageBitmap) {
image.setImageBitmap(imageBitmap);
notifyDataSetChanged(); }
});
} catch (MalformedURLException e) {
Log.e(TAG, "Bad remote image URL: " + pro.smallImageUrl, e);
}
textTitle.setText(pro.project_title);
if( cachedImage != null ) {
image.setImageBitmap(cachedImage);
}
return projectView;
}
}
推荐答案
我在此代码加载器代码 ..
检查该代码..
1.在活动"中，获取字符串数组"中的所有图像URL并将其传递..
1.In your Activity get all the images URL in String Array and pass it..
dealAdapter = new LazyAdapter(Activityname.this,VALUE_image);
其中VALUE_image包含您的图像.
where VALUE_image contains your images.
重要的是检查是否在清单文件中添加权限
Important thing is that check whether you add permission in Manifest file
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>
创建一个文件，即ImageLoader.class，然后粘贴该链接中提供的Image Loader的代码
Create a file namelyImageLoader.class and paste the code of Image Loader given in that link
然后创建文件Utils.class并将Utils的代码粘贴到该链接中.
Then create file namely Utils.class and paste code of Utils in that link.
在上面的代码中，它检查是否存在Sdcard(如果存在)，然后在Sdcard中创建文件夹，并以压缩格式存储所有图像，并在以后检索.
In the above code it checks whether Sdcard is present if so the create folder in Sdcard and store all images in compressed format and retrive it later..
否则，如果没有，它将图像存储在高速缓存中.
Else if no it store images in Cache memory..
第一次从服务器加载图像，然后再次检查是否在Sdcard或高速缓存中，如果是，则检索图像并显示.
First time its load image from the server and next time it check whether it is in Sdcard or in Cache Memory if so retrive the image and Displays..
检查一下.
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