android - 在 Android 中将所有文件读入列表的最有效方法

Question

我的 Android 应用程序需要查看默认的相机目录并获取在某个时间范围内创建的 JPEG 文件的名称。我目前使用以下代码 fragment 执行此操作。这个想法是不仅通过“jpg”扩展名过滤掉文件，而且利用文件名中包含日期/时间这一事实。

我在线程中运行下面的 getImages() 函数，因此 UI 本身不受影响。我注意到即使在这之后目录中有很多文件也需要一段时间。是否有更快的算法或 Android 特定功能可用于进一步优化它？

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;
    }

这是我使用的过滤器类

class JpegFilter implements FilenameFilter {
    public boolean accept(File dir, String name) {
        return (name.startsWith(captureJPEG.filterString) && name.endsWith(".jpg"));
    }
}

Answer 1

参见 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;
}