所以我创建了一个在网络上与JSON通信的应用程序。它从JSON中获取图像和文本。 现在我有一项任务是在没有互联网连接的情况下访问此应用程序。 它应该是这样的：
第一次启动时，应用程序必须检查是否有任何互联网连接。如果没有，请弹出一个对话框'请检查您的互联网连接'。 如果有的话，应用程序已打开，必须从JSON下载图像和文本并将其保存到外部存储
下次打开应用程序时，如果没有互联网，它将从外部存储装载图像和文本文件。每次连接到互联网时，它都会下载文件并替换以前的文件。
有人可以通过修改下面的这些类来为我提供解决方案吗？
public class ImageThreadLoader {
private static final String TAG = "ImageThreadLoader";
// Global cache of images.
// Using SoftReference to allow garbage collector to clean cache if needed
private final HashMap<String, SoftReference<Bitmap>> Cache = new HashMap<String, SoftReference<Bitmap>>();
private final class QueueItem {
public URL url;
public ImageLoadedListener listener;
}
private final ArrayList<QueueItem> Queue = new ArrayList<QueueItem>();
private final Handler handler = new Handler(); // Assumes that this is started from the main (UI) thread
private Thread thread;
private QueueRunner runner = new QueueRunner();;
/** Creates a new instance of the ImageThreadLoader */
public ImageThreadLoader() {
thread = new Thread(runner);
}
/**
* Defines an interface for a callback that will handle
* responses from the thread loader when an image is done
* being loaded.
*/
public interface ImageLoadedListener {
public void imageLoaded(Bitmap imageBitmap );
}
/**
* Provides a Runnable class to handle loading
* the image from the URL and settings the
* ImageView on the UI thread.
*/
private class QueueRunner implements Runnable {
public void run() {
synchronized(this) {
while(Queue.size() > 0) {
final QueueItem item = Queue.remove(0);
// If in the cache, return that copy and be done
if( Cache.containsKey(item.url.toString()) && Cache.get(item.url.toString()) != null) {
// Use a handler to get back onto the UI thread for the update
handler.post(new Runnable() {
public void run() {
if( item.listener != null ) {
// NB: There's a potential race condition here where the cache item could get
// garbage collected between when we post the runnable and it's executed.
// Ideally we would re-run the network load or something.
SoftReference<Bitmap> ref = Cache.get(item.url.toString());
if( ref != null ) {
item.listener.imageLoaded(ref.get());
}
}
}
});
} else {
final Bitmap bmp = readBitmapFromNetwork(item.url);
if( bmp != null ) {
Cache.put(item.url.toString(), new SoftReference<Bitmap>(bmp));
// Use a handler to get back onto the UI thread for the update
handler.post(new Runnable() {
public void run() {
if( item.listener != null ) {
item.listener.imageLoaded(bmp);
}
}
});
}
}
}
}
}
}
/**
* Queues up a URI to load an image from for a given image view.
*
* @param uri The URI source of the image
* @param callback The listener class to call when the image is loaded
* @throws MalformedURLException If the provided uri cannot be parsed
* @return A Bitmap image if the image is in the cache, else null.
*/
public Bitmap loadImage( final String uri, final ImageLoadedListener listener) throws MalformedURLException {
// If it's in the cache, just get it and quit it
if( Cache.containsKey(uri)) {
SoftReference<Bitmap> ref = Cache.get(uri);
if( ref != null ) {
return ref.get();
}
}
QueueItem item = new QueueItem();
item.url = new URL(uri);
item.listener = listener;
Queue.add(item);
// start the thread if needed
if( thread.getState() == State.NEW) {
thread.start();
} else if( thread.getState() == State.TERMINATED) {
thread = new Thread(runner);
thread.start();
}
return null;
}
/**
* Convenience method to retrieve a bitmap image from
* a URL over the network. The built-in methods do
* not seem to work, as they return a FileNotFound
* exception.
*
* Note that this does not perform any threading --
* it blocks the call while retrieving the data.
*
* @param url The URL to read the bitmap from.
* @return A Bitmap image or null if an error occurs.
*/
public static Bitmap readBitmapFromNetwork( URL url ) {
InputStream is = null;
BufferedInputStream bis = null;
Bitmap bmp = null;
try {
URLConnection conn = url.openConnection();
conn.connect();
is = conn.getInputStream();
bis = new BufferedInputStream(is);
bmp = BitmapFactory.decodeStream(bis);
} catch (MalformedURLException e) {
Log.e(TAG, "Bad ad URL", e);
} catch (IOException e) {
Log.e(TAG, "Could not get remote ad image", e);
} finally {
try {
if( is != null )
is.close();
if( bis != null )
bis.close();
} catch (IOException e) {
Log.w(TAG, "Error closing stream.");
}
}
return bmp;
}
}
和
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;
}
}
谢谢！
答案 0 :(得分：0)
使用下载图像的名称和路径创建数据库。在onCreate（）（或您想要进行检查的任何地方），读取数据库并检查它是否为空。如果没有，则使用图像。