[英]Most efficient way to read all files into a list in Android
我的Android應用程序需要查看默認的Camera目錄,並獲取在一個時間范圍內創建的JPEG文件的名稱。 我目前使用以下代碼段執行此操作。 想法是不僅通過“ jpg”擴展名過濾文件,而且使用文件名中包含日期/時間這一事實。
我在Thread中運行以下getImages()函數,因此UI本身不受影響。 我注意到,即使在所有這些之后,如果目錄中有很多文件也要花費一些時間。 是否可以使用更快的算法或Android特定功能進一步優化它?
private boolean getImages()
{
boolean status=true;
File dir = new File(picPath);
//Optimize file search by setting the common file prefix as a filter
//get the date format used by camera to store files.
String startStr=startTime.format3339(false);
String endStr=endTime.format3339(false);
//Loop through each character of start time
//and compare with end time till a mismatch is found
int len=startStr.length();
int idx=0;
for ( idx=0;id < len;idx++ )
{
if (startStr.charAt(idx) != endStr.charAt(idx))
{
Log.d(TAG,"breaking at idx "+ idx);
break;
}
}
filterString=endStr.substring(0,idx).replace("T", " ").replace(":",".");
Log.d(TAG,"Filter String" + filterString);
String[] children = dir.list(new JpegFilter());
List matchedFiles = new ArrayList();
Log.d(TAG,dir.getAbsolutePath()+" has "+ children.length+ " files");
int numfiles = children.length;
for(int i=0;i < numfiles;i++)
{
//Get file modify time
File file = new File(picPath+File.separator+children[i]);
// Get the last modification information.
long lastModified = file.lastModified();
if (lastModified > =startTime.toMillis(false)) //If file modified date greater than equals start time
{
Log.d(TAG,"Match! " + children[i]);
if (lastModified < =endTime.toMillis(false))//If file modified date less than equals end time
{
matchedFiles.add(picPath+File.separator+children[i]);
}
else //We are now over the time range, quit loop to save time
{
break; //TODO break out of for loop
}
}
}
if (!matchedFiles.isEmpty()) //If there are images to be processed
{
status=convertToPDF(matchedFiles,pdfFile);
Log.d(TAG,"convertToPDF() returned " + status);
}
return status;
}
這是我使用的Filter類
class JpegFilter implements FilenameFilter {
public boolean accept(File dir, String name) {
return (name.startsWith(captureJPEG.filterString) && name.endsWith(".jpg"));
}
}
參見http://androidworkz.com/2010/07/08/source-code-find-files-by-type-play-media-file/
public class FileUtils {
public File[] listFilesAsArray(File directory, FilenameFilter[] filter,
int recurse) {
Collection<File> files = listFiles(directory, filter, recurse);
File[] arr = new File[files.size()];
return files.toArray(arr);
}
public Collection<File> listFiles(File directory,
FilenameFilter[] filter, int recurse) {
Vector<File> files = new Vector<File>();
File[] entries = directory.listFiles();
if (entries != null) {
for (File entry : entries) {
for (FilenameFilter filefilter : filter) {
if (filter == null
|| filefilter
.accept(directory, entry.getName())) {
files.add(entry);
Log.v("FileUtils", "Added: "
+ entry.getName());
}
}
if ((recurse <= -1) || (recurse > 0 && entry.isDirectory())) {
recurse--;
files.addAll(listFiles(entry, filter, recurse));
recurse++;
}
}
}
return files;
}
}
您是否看過此處編寫的Android File Browser示例? 也許您可以使用此示例並針對您的特定需求進行調整。 我不確定這是否會更快,但是這是考慮使用其他方法實現目標的一個很好的起點。
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