Load Random Images from Directory

问题:

I'd like to randomly load images from a directory and have a button somewhere that refreshes the entire page. Here's the current code I have now:

<?php
$a = array();
$dir = '../public/wp-content/uploads/2012/01';
if ($handle = opendir($dir)) {
  while (false !== ($file = readdir($handle))) {
    if (preg_match("/\.png$/", $file)) $a[] = $file;
    elseif (preg_match("/\.jpg$/", $file)) $a[] = $file;
    elseif (preg_match("/\.jpeg$/", $file)) $a[] = $file;
  }
  closedir($handle);
}

foreach ($a as $i) {

  echo "<img src='" . $dir . '/' . $i . "' />";

}

?>  

The problem is it loads all 400,000 images at once. I only want 30 to load. 30 random images from the directory. I tried looking up some code such as modifying the above to this:

<?php
$a = array();
$dir = '../public/wp-content/uploads/2012/01';
if ($handle = opendir($dir)) {
  while (false !== ($file = readdir($handle))) {
    if (preg_match("/\.png$/", $file)) $a[] = $file;
    elseif (preg_match("/\.jpg$/", $file)) $a[] = $file;
    elseif (preg_match("/\.jpeg$/", $file)) $a[] = $file;
  }
  closedir($handle);
}

foreach ($a as $i) {

  echo "<img src='" . $dir . '/' . $i . "' />";
  if (++$i == 2) break;

}

?>  

But it seems to do absolutely nothing.. So if someone can help me get 30 random photos from that directory to load and have some type of reload button, that would be of great help.

Thank you in advance

回答1:

Here is my solution with a cache:

<?php

define('CACHE_FILE', 'mycache.tmp');
define('CACHE_TIME', 20); // 20 seconds (for testing!)
define('IMG_COUNT', 30);
define('IMG_DIR', '../public/wp-content/uploads/2012/01');

/**
  * Loads the list (an array) from the cache
  * Returns FALSE if the file couldn't be opened or the cache was expired, otherwise the list (as an array) will be returned.
  */
function LoadListFromCache($cacheFile, $cacheTime)
{
  if ( file_exists($cacheFile) )
  {
    $fileHandle = fopen($cacheFile, 'r');
    if ( !$fileHandle )
      return false;

    // Read timestamp (separated by "\n" from the content)
    $timestamp = intval( fgets($fileHandle) );
    fclose($fileHandle);
    // Expired?
    if ( $timestamp+$cacheTime > time() )
      return false;
    else
    {
      // Unserialize the content!
      $content = file_get_contents($cacheFile);
      $content = substr( $content, strpos($content, "\n") );

      $list = unserialize($content);
      return $list;
    }
  }
  return false;
}

/**
  * Caches the passed array
  * Returns FALSE if the file couldn't be opened, otherwise TRUE.
  */
function SaveListToCache($cacheFile, $list)
{
  $fileHandle = fopen($cacheFile, 'w');
  if ( $fileHandle === FALSE ) return false;

  fwrite($fileHandle, time());
  fwrite($fileHandle, "\n");
  fwrite($fileHandle, serialize($list));

  fclose($fileHandle);
  return true;
}

/**
  * Generates the list of all image files (png, jpg, jpeg) and caches it.
  * Returns the list as an array.
  */
function GenerateList()
{
  $a = array();
  $dir = IMG_DIR;
  if ($handle = opendir($dir))
  {
    while (false !== ($file = readdir($handle)))
    {
      if (preg_match("/\.png$/", $file)) $a[] = $file;
      elseif (preg_match("/\.jpg$/", $file)) $a[] = $file;
      elseif (preg_match("/\.jpeg$/", $file)) $a[] = $file;
    }
    closedir($handle);
  }
  SaveListToCache(CACHE_FILE, $a);
  return $a;
}

function GetRandomImages($list, $count)
{
  $listCount = count($list);
  $randomEntries = array();

  for ($i=0; $i<$count; $i++)
  {
    $randomEntries[] = $list[ rand(0, $listCount) ];
  }
  return $randomEntries;
}

// This code will execute the other functions!

$list = LoadListFromCache(CACHE_FILE, CACHE_TIME);

if ( $list === FALSE )
{
  $list = GenerateList();
}
$images = GetRandomImages($list, IMG_COUNT);

foreach ($images as $image)
{
  echo '<img src="', IMG_DIR.DIRECTORY_SEPARATOR.$image, '" />';
}

回答2:

If you have 400,000 images then I think reading the entire directory everytime is going to be an expensive means of showing random images. I would use a database instead and store the file paths in it.

If you want to use your existing code then think of it this way. You have an array of length n containing image names. You want to generate thirty random numbers between 0 and n-1. Then display the image associated with that position in the array. I'm not a php expert, but here is some pseudocode:

$a = array(); 
$dir = '../public/wp-content/uploads/2012/01';

if (preg_match("/\.png$/", $file)) $a[] = $file;
elseif (preg_match("/\.jpg$/", $file)) $a[] = $file;
elseif (preg_match("/\.jpeg$/", $file)) $a[] = $file;

for ( i=0; i < 30; i++) {
     //generate a random number between 0 and N-1
     random = rand(0, $a.length - 1);
     //display that image in the array
     echo "<img src='" . $dir . '/' . $a[random] . "' />";
}

回答3:

You need to create a new variable for the counter instead of using $i

For example, you can do this instead

$j = 0;
foreach ($a as $i) {
  echo "<img src='" . $dir . '/' . $i . "' />";
  $j++;
  if ($j >= 30)
  {
    break;
  }

}

EDIT: Perhaps for the random part you can first generate a random number between 0 and n-1 where n is the total number of the images and then just echo out the image from the array with the index number.

Instead of using foreach, I think you'll need a for loop instead.

$totalImgs = count($a);
$imgUsed = array();
for ($j = 0; $j < 30; $j++)
{
    do
    {
        $randIndex = mt_rand(0, $totalImgs);
    }
    while ($imgUsed[$randIndex] === TRUE);
    $imgUsed[$randIndex] = TRUE;
    echo "<img src='" . $dir . '/' . $a[$randIndex] . "' />";
}

回答4:

You should maybe only read 30 file from your directory. Stop looking in the directory when readdir return false or your array's length is 30.

This should work

    $a = array();
$dir = '../public/wp-content/uploads/2012/01';
if ($handle = opendir($dir)) {
  while (false !== ($file = readdir($handle)) && (count($a) <= 30) {
    if (preg_match("/\.png$/", $file)) $a[] = $file;
    elseif (preg_match("/\.jpg$/", $file)) $a[] = $file;
    elseif (preg_match("/\.jpeg$/", $file)) $a[] = $file;
  }
  closedir($handle);
}

It may not execute (I didn't try). But the idea is here

For randomize the image: shuffle($a) should do the trick

回答5:

in simplest way , you can use

find , sort , head 

commands in linux,in conjuction with PHP's built in

exec()

function to get 30 random image links easily , the folowing snippet lists how to do it (How to get random 30 image links in an array.)

<?php
$picdir = "directory/containing/pictures"; // directory containing only pictures
exec("find " . $picdir . " | sort -R | head -30 ",$links);
while(list($index,$val) = each($links) ) {
    echo "<img src =" .$val . "> <br/>";  // shows image 
}

?> Here $links array contain random 30 image names(from folder) with complete path . This is used with img tag in echo to generate images

Here $picdir has the path of the directory having images and it is assumed that dirrectory is having only image files . in other case its only matter of modifying find command to exclude non image files(such as using grep command to exclude )