如何获取mPDF 7的PDF生成进度信息？

Great question! I’ve dealt with this exact frustration when generating large PDFs with mPDF 7.x—waiting around without any progress feedback is no fun. Let’s walk through your options to add progress tracking, since the old HTML progress bar feature was indeed removed in version 7.0.

1. Implement Custom Page-Based Callbacks #

mPDF doesn’t have built-in callback hooks, but you can extend the core Mpdf class to add your own page-tracking logic. The idea is to override the internal method that runs when a page finishes rendering, then trigger your callback each time (or every X pages).

Here’s a working example:

class ProgressMpdf extends \Mpdf\Mpdf {
    private $pageCallback;
    private $currentPage = 0;

    // Set up a method to register your callback function
    public function onPageGenerated(callable $callback) {
        $this->pageCallback = $callback;
    }

    // Override the internal _endpage method to trigger our callback
    protected function _endpage() {
        parent::_endpage(); // Keep mPDF's original functionality
        $this->currentPage++;

        // Fire the callback if it's set
        if ($this->pageCallback) {
            call_user_func($this->pageCallback, $this->currentPage);
        }
    }
}

Usage Example: #

// Initialize our custom mPDF instance
$mpdf = new ProgressMpdf();

// Register a callback that triggers every 5 pages
$mpdf->onPageGenerated(function($pageNum) {
    if ($pageNum % 5 === 0) {
        echo "Generated page $pageNum...\n";
        // For web environments, force output to the browser immediately
        ob_flush();
        flush();
    }
});

// Load your HTML and generate the PDF
$mpdf->WriteHTML($yourLargeHtmlContent);
$mpdf->Output();

2. Track Progress by HTML Chunks #

If you want to trigger callbacks based on the amount of HTML processed (instead of pages), split your HTML into smaller chunks and process them one by one. This lets you calculate progress based on the total size of your input.

$htmlContent = file_get_contents('large-document.html');
$chunkSize = 10240; // Split into 10KB chunks
$chunks = str_split($htmlContent, $chunkSize);
$totalChunks = count($chunks);
$processedChunks = 0;

$mpdf = new \Mpdf\Mpdf();

foreach ($chunks as $chunk) {
    $processedChunks++;
    $mpdf->WriteHTML($chunk);

    // Calculate and output progress
    $progressPercent = round(($processedChunks / $totalChunks) * 100, 2);
    echo "Processed $progressPercent% of HTML content...\n";
    ob_flush();
    flush();
}

$mpdf->Output();

3. Combine Page Tracking with Estimated Total Pages #

For more accurate progress percentages, first estimate the total number of pages your document will have, then pair that with the page-based callback. This gives users a clear "X% complete" metric.

// First, quickly estimate the total page count
$pageEstimator = new \Mpdf\Mpdf();
$pageEstimator->WriteHTML($yourLargeHtmlContent);
$totalPages = $pageEstimator->PageCount();

// Now use our custom ProgressMpdf class
$mpdf = new ProgressMpdf();
$mpdf->onPageGenerated(function($currentPage) use ($totalPages) {
    $progress = round(($currentPage / $totalPages) * 100, 2);
    echo "Progress: $progress% ($currentPage/$totalPages pages)\n";
    ob_flush();
    flush();
});

$mpdf->WriteHTML($yourLargeHtmlContent);
$mpdf->Output();

Notes for Web Environments #

• Make sure output buffering is configured correctly so progress updates reach the browser in real-time.
• Avoid using compression (like gzip) for the response, as it can delay output until the entire PDF is generated.

内容的提问来源于stack exchange，提问作者Michael Große