我之前也做过同样的事情。你需要传递一个包含图片的文件夹名称给setBaseFolder
方法。这个方法会调用refresh()
,使用一个FilenameFilter
(代码未包含但很容易实现)从那个文件夹中获取所有名为orig_....jpg
的图片,并将其保存在mFileList
中。然后我们调用notifyDataSetChanged()
,这将触发每个单元格的getView()
。
现在,在getView()
中,如果我们已经有缩略图位图,则从缓存中获取它,否则我们会创建一个灰色占位符并启动一个ThumbnailBuilder
来创建缩略图或获取位图。
我认为你需要稍微修改一下ThumbnailBuilder
,因为我创建的“缩略图”相当大(500x500),因为我还需要调整大小的图像用于其他目的。此外,由于我使用相机拍摄的照片,所以还有一些内容,根据exif信息旋转图像。但基本上,ThumbnailBuilder
只是检查是否已经有缩略图图像(我的缩略图图像与原始图像放置在同一个文件夹中,但前缀为small_
而不是orig_
)-如果缩略图图片已经存在,则我们将其作为Bitmap
获取并完成,否则将生成图像。最后,在onPostExecute()
中,位图被设置到ImageView中。
public class PhotoAdapter extends BaseAdapter {
private Context mContext;
private int mCellSize;
private File mFolder;
private File[] mFileList;
private Map<Object, Bitmap> mThumbnails = new HashMap<Object, Bitmap>();
private Set<Object> mCreatingTriggered = new HashSet<Object>();
public PhotoAdapter(Context context, int cellSize) {
mContext = context;
mCellSize = cellSize;
}
@Override
public int getCount() {
if (mFolder == null) {
return 0;
} else {
return mFileList.length;
}
}
@Override
public Object getItem(int position) {
return mFileList[position];
}
@Override
public long getItemId(int position) {
return position;
}
@Override
public View getView(int position, View convertView, ViewGroup parent) {
ImageView view = (ImageView)convertView;
if (view == null) {
view = new ImageView(mContext);
view.setLayoutParams(new GridView.LayoutParams(mCellSize, mCellSize));
view.setScaleType(ImageView.ScaleType.CENTER_CROP);
view.setPadding(8, 8, 8, 8);
view.setBackgroundColor(0xFFC6CCD3);
}
Object item = getItem(position);
Bitmap bm = mThumbnails.get(item);
if (bm == null) {
view.setImageBitmap(null);
if (!mCreatingTriggered.contains(item)) {
mCreatingTriggered.add(item);
new ThumbnailBuilder(view, (File)item).execute();
}
} else {
view.setImageBitmap(bm);
}
return view;
}
public void setBaseFolder(File baseFolder) {
if (baseFolder == null) return;
if (!baseFolder.equals(mFolder)) {
releaseThumbnails();
mFolder = baseFolder;
}
refresh();
}
public void refresh() {
if (mFolder == null) {
return;
}
mFileList = mFolder.listFiles(EtbApplication.origImageFilenameFilter);
if (mFileList == null) mFileList = new File[0];
notifyDataSetChanged();
}
public void releaseThumbnails() {
for (Bitmap bm : mThumbnails.values()) {
bm.recycle();
}
mThumbnails.clear();
}
private class ThumbnailBuilder extends AsyncTask<Void, Integer, Bitmap> {
private ImageView mView;
private File mFile;
public ThumbnailBuilder(ImageView view, File file) {
mView = view;
mFile = file;
}
@Override
protected Bitmap doInBackground(Void... params) {
Log.d("adapter", "make small image and thumbnail");
try {
return createThumbnail(mFile.getAbsolutePath());
} catch (Exception e) {
return null;
}
}
@Override
protected void onPostExecute(Bitmap result) {
if (result != null) {
mView.setImageBitmap(result);
mThumbnails.put(mFile, result);
} else {
mView.setImageResource(R.drawable.ic_launcher);
}
}
private Bitmap createThumbnail(String file) throws IOException {
File thumbnailFile = new File(file.replace("orig_", "small_"));
if (thumbnailFile.exists()) {
return BitmapFactory.decodeFile(thumbnailFile.getAbsolutePath());
}
BitmapFactory.Options bounds = new BitmapFactory.Options();
bounds.inJustDecodeBounds = true;
BitmapFactory.decodeFile(file, bounds);
if ((bounds.outWidth == -1) || (bounds.outHeight == -1))
return null;
int w, h;
if (bounds.outWidth > bounds.outHeight) {
w = 500;
h = 500 * bounds.outHeight / bounds.outWidth;
} else {
h = 500;
w = 500 * bounds.outWidth / bounds.outHeight;
}
BitmapFactory.Options opts = new BitmapFactory.Options();
opts.inSampleSize = 4;
Bitmap resizedBitmap = BitmapFactory.decodeFile(file, opts);
resizedBitmap = Bitmap.createScaledBitmap(resizedBitmap, w, h, true);
ExifInterface exif = new ExifInterface(file);
String orientString = exif.getAttribute(ExifInterface.TAG_ORIENTATION);
int orientation = orientString != null ? Integer.parseInt(orientString) : ExifInterface.ORIENTATION_NORMAL;
int rotationAngle = 0;
if (orientation == ExifInterface.ORIENTATION_ROTATE_90) rotationAngle = 90;
if (orientation == ExifInterface.ORIENTATION_ROTATE_180) rotationAngle = 180;
if (orientation == ExifInterface.ORIENTATION_ROTATE_270) rotationAngle = 270;
Matrix matrix = new Matrix();
matrix.setRotate(rotationAngle, (float) resizedBitmap.getWidth() / 2, (float) resizedBitmap.getHeight() / 2);
Bitmap rotatedBitmap = Bitmap.createBitmap(resizedBitmap, 0, 0, w, h, matrix, true);
resizedBitmap.recycle();
ByteArrayOutputStream bytes = new ByteArrayOutputStream();
rotatedBitmap.compress(Bitmap.CompressFormat.JPEG, 90, bytes);
thumbnailFile.createNewFile();
FileOutputStream fo = new FileOutputStream(thumbnailFile);
fo.write(bytes.toByteArray());
fo.close();
return rotatedBitmap;
}
}
}