/** 清除数据库中暂存的缩略图信息及对应的缩略图文件，需要在每次退出程序前清除过时的信息，只保留MaxThumbnailNum个缩略图信息， 防止暂存区不断扩大 */
public void clearThumbnailData() {
final int ORIG_PATH_COLUMN = 0;
final int THUMB_PATH_COLUMN = 1;
final int CREATE_TIME = 2;
String[] columns = {
ImageDatabase.ORIG_PATH, ImageDatabase.THUMB_PATH, ImageDatabase.CREATE_TIME
};
String sort = ImageDatabase.CREATE_TIME + " DESC";
// 按降序整理查询的结果
Cursor c = imageDB.query(columns, null, null, sort);
int i = 0;
if (c != null) {
try {
while (c.moveToNext()) {
i++;
// 删除第MaxThumbnailNum以后个图片及其信息
if (i > MaxThumbnailNum) {
String thumbPath = c.getString(THUMB_PATH_COLUMN);
String origPath = c.getString(ORIG_PATH_COLUMN);
File file = new File(thumbPath);
try {
if (file.delete()) {
imageDB.delete(origPath);
}
} catch (SecurityException e) {
}
}
}
} finally {
c.close();
c = null;
}
} else {
Log.d(TAG, "cursor is null");
}
}
/**
* 从数据库中查询返回缩略图
*
* @param origPath
* @return null如果查询不到该缩略图文件
*/
public Bitmap getImageThumbFromDB(String origPath) {
final int ORIG_PATH_COLUMN = 0;
final int THUMB_PATH_COLUMN = 1;
String[] columns = {ImageDatabase.ORIG_PATH, ImageDatabase.THUMB_PATH};
String selection = ImageDatabase.ORIG_PATH + "=?";
String Args[] = {origPath};
Bitmap thumbnail = null;
Cursor c = imageDB.query(columns, selection, Args, null);
// 如果从数据库中找到该原图的缩量图，则直接使用
if (c != null) {
try {
while (c.moveToNext()) {
String thumbPath = c.getString(THUMB_PATH_COLUMN);
thumbnail = BitmapFactory.decodeFile(thumbPath);
break;
}
} finally {
c.close();
c = null;
}
}
return thumbnail;
}
