在主要活动中：-
public class Main extends Activity {
String mImagesPath;
/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
mImagesPath = this.getFilesDir().getParent() + "/images/";
createImagesDir(mImagesPath);
copyImagesToStorage();
loadGridView();
}
/**
* Method handles the logic for setting the adapter for the gridview
*/
private void loadGridView(){
GridView lLazyGrid = (GridView) this.findViewById(R.id.gridview);
try {
LazyImageAdapter lLazyAdapter = new LazyImageAdapter(this.getApplicationContext(),
null,
mImagesPath);
lLazyGrid.setAdapter(lLazyAdapter);
} catch (Exception e) {
e.printStackTrace();
}
}
/**
* Copy images from assets to storage
*/
private void copyImagesToStorage(){
AssetManager lAssetManager = getAssets();
String[] lFiles = null;
String lTag = "copyImageFail";
try {
// get all of the files in the assets directory
lFiles = lAssetManager.list("");
} catch (IOException e) {
Log.e(lTag, e.getMessage());
}
for(int i=0; i<lFiles.length; i++) {
// We have a file to copy
try {
// copy the file
copyFile(lFiles[i], mImagesPath + lFiles[i]);
} catch(Exception e) {
Log.e(lTag, e.getMessage());
}
}
}
/**
* Method copies the contents of one stream to another
* @param aIn stream to copy from
* @param aOut stream to copy to
* @throws IOException
*/
private void copyFile(String aIn, String aOut) throws IOException {
byte[] lBuffer = new byte[1024];
int lRead;
final int lOffset = 0;
// create an in and out stream
InputStream lIn = getAssets().open(aIn);
OutputStream lOut = new FileOutputStream(aOut);
// Copy contents while there is data
while((lRead = lIn.read(lBuffer)) != -1){
lOut.write(lBuffer, lOffset, lRead);
}
// clean up after our streams
lIn.close();
lIn = null;
lOut.flush();
lOut.close();
lOut = null;
}
/**
* Create the directory specified at aPath if it does not exist
* @param aPath directory to check for and create
*/
private void createImagesDir(String aPath){
File lDir = new File(aPath);
if(!lDir.exists()){
lDir.mkdir();
}
}
}
======================================
在 ImageLoader 类中：
public class ImageLoader extends Thread {
public interface ImageLoadListener {
void handleImageLoaded(ViewSwitcher aViewSwitcher, ImageView aImageView, Bitmap aBitmap);
}
private static final String TAG = ImageLoader.class.getSimpleName();
ImageLoadListener mListener = null;
private Handler handler;
/**
* Image loader takes an object that extends ImageLoadListener
* @param lListener
*/
ImageLoader(ImageLoadListener lListener){
mListener = lListener;
}
@Override
public void run() {
try {
// preparing a looper on current thread
// the current thread is being detected implicitly
Looper.prepare();
// Looper gets attached to the current thread by default
handler = new Handler();
Looper.loop();
// Thread will start
} catch (Throwable t) {
Log.e(TAG, "ImageLoader halted due to a error: ", t);
}
}
/**
* Method stops the looper and thus the thread
*/
public synchronized void stopThread() {
// Use the handler to schedule a quit on the looper
handler.post(new Runnable() {
public void run() {
// This runs on the ImageLoader thread
Log.i(TAG, "DownloadThread loop quitting by request");
Looper.myLooper().quit();
}
});
}
/**
* Method queues the image at path to load
* Note that the actual loading takes place in the UI thread
* the ImageView and ViewSwitcher are just references for the
* UI thread.
* @param aPath - Path where the bitmap is located to load
* @param aImageView - The ImageView the UI thread will load
* @param aViewSwitcher - The ViewSwitcher that needs to display the imageview
*/
public synchronized void queueImageLoad(
final String aPath,
final ImageView aImageView,
final ViewSwitcher aViewSwitcher) {
// Wrap DownloadTask into another Runnable to track the statistics
handler.post(new Runnable() {
public void run() {
try {
synchronized (aImageView){
// make sure this thread is the only one performing activities on
// this imageview
BitmapFactory.Options lOptions = new BitmapFactory.Options();
lOptions.inSampleSize = 1;
Bitmap lBitmap = BitmapFactory.decodeFile(aPath, lOptions);
//aImage.setImageBitmap(lBitmap);
// Load the image here
signalUI(aViewSwitcher, aImageView, lBitmap);
}
}
catch(Exception e){
e.printStackTrace();
}
}
});
}
/**
* Method is called when the bitmap is loaded. The UI thread adds the bitmap to the imageview.
* @param aViewSwitcher - The ViewSwitcher that needs to display the imageview
* @param aImageView - The ImageView the UI thread will load
* @param aImage - The Bitmap that gets loaded into the ImageView
*/
private void signalUI(
ViewSwitcher aViewSwitcher,
ImageView aImageView,
Bitmap aImage){
if(mListener != null){
// we have an object that implements ImageLoadListener
mListener.handleImageLoaded(aViewSwitcher, aImageView, aImage);
}
}
}
=======================================
在 LazyImageAdapter 中：
public class LazyImageAdapter extends BaseAdapter implements ImageLoadListener {
private static final int PROGRESSBARINDEX = 0;
private static final int IMAGEVIEWINDEX = 1;
private Context mContext = null;
private OnClickListener mItemClickListener;
private Handler mHandler;
private ImageLoader mImageLoader = null;
private File mDirectory;
/**
* Lazy loading image adapter
* @param aContext
* @param lClickListener click listener to attach to each item
* @param lPath the path where the images are located
* @throws Exception when path can't be read from or is not a valid directory
*/
public LazyImageAdapter(
Context aContext,
OnClickListener lClickListener,
String lPath
) throws Exception {
mContext = aContext;
mItemClickListener = lClickListener;
mDirectory = new File(lPath);
// Do some error checking
if(!mDirectory.canRead()){
throw new Exception("Can't read this path");
}
else if(!mDirectory.isDirectory()){
throw new Exception("Path is a not a directory");
}
mImageLoader = new ImageLoader(this);
mImageLoader.start();
mHandler = new Handler();
}
@Override
protected void finalize() throws Throwable {
// TODO Auto-generated method stub
super.finalize();
// stop the thread we started
mImageLoader.stopThread();
}
public int getCount() {
return mDirectory.listFiles().length;
}
public Object getItem(int aPosition) {
String lPath = null;
File []lFiles = mDirectory.listFiles();
if(aPosition < lFiles.length){
lPath = mDirectory.listFiles()[aPosition].getAbsolutePath();
}
return lPath;
}
public long getItemId(int arg0) {
// TODO Auto-generated method stub
return 0;
}
public View getView(final int aPosition, View aConvertView, ViewGroup parent) {
final ViewSwitcher lViewSwitcher;
String lPath = (String)getItem(aPosition);
// logic for conserving resources see google video on making your ui fast
// and responsive
if (null == aConvertView) {
lViewSwitcher = new ViewSwitcher(mContext);
lViewSwitcher.setPadding(8, 8, 8, 8);
ProgressBar lProgress = new ProgressBar(mContext);
lProgress.setLayoutParams(new ViewSwitcher.LayoutParams(80, 80));
lViewSwitcher.addView(lProgress);
ImageView lImage = new ImageView(mContext);
lImage.setLayoutParams(new ViewSwitcher.LayoutParams(100, 100));
lViewSwitcher.addView(lImage);
// attach the onclick listener
lViewSwitcher.setOnClickListener(mItemClickListener);
} else {
lViewSwitcher = (ViewSwitcher) aConvertView;
}
ViewTagInformation lTagHolder = (ViewTagInformation) lViewSwitcher
.getTag();
if (lTagHolder == null ||
!lTagHolder.aImagePath.equals(lPath)) {
// The Tagholder is null meaning this is a first time load
// or this view is being recycled with a different image
// Create a ViewTag to store information for later
ViewTagInformation lNewTag = new ViewTagInformation();
lNewTag.aImagePath = lPath;
lViewSwitcher.setTag(lNewTag);
// Grab the image view
// Have the progress bar display
// Then queue the image loading
ImageView lImageView = (ImageView) lViewSwitcher.getChildAt(1);
lViewSwitcher.setDisplayedChild(PROGRESSBARINDEX);
mImageLoader.queueImageLoad(lPath, lImageView, lViewSwitcher);
}
return lViewSwitcher;
}
public void handleImageLoaded(
final ViewSwitcher aViewSwitcher,
final ImageView aImageView,
final Bitmap aBitmap) {
// The enqueue the following in the UI thread
mHandler.post(new Runnable() {
public void run() {
// set the bitmap in the ImageView
aImageView.setImageBitmap(aBitmap);
// explicitly tell the view switcher to show the second view
aViewSwitcher.setDisplayedChild(IMAGEVIEWINDEX);
}
});
}
}
/**
* View holder pattern as described in google sample code
* we may want to add more attributes to this if the path was
* say being stored in a sqlite database
* @author bacaj
*/
class ViewTagInformation {
String aImagePath;
}