# Zend_ProgressBar

## Introduction

`Zend_ProgressBar` is a component to create and update progressbars in different environments. It consists of a single backend, which outputs the progress through one of the multiple adapters. On every update, it takes an absolute value and optionally a status message, and then calls the adapter with some precalculated values like percentage and estimated time left.

## Basic Usage of Zend_Progressbar

`Zend_ProgressBar` is quite easy in its usage. You simply create a new instance of `Zend_Progressbar`, defining a min- and a max-value, and choose an adapter to output the data. If you want to process a file, you would do something like:

    $progressBar = new Zend_ProgressBar($adapter, 0, $fileSize);

    while (!feof($fp)) {
        // Do something

        $progressBar->update($currentByteCount);
    }

    $progressBar->finish();

In the first step, an instance of `Zend_ProgressBar` is created, with a specific adapter, a min-value of 0 and a max-value of the total filesize. Then a file is processed and in every loop the progressbar is updated with the current byte count. At the end of the loop, the progressbar status is set to finished.

You can also call the `update()` method of `Zend_ProgressBar` without arguments, which just recalculates ETA and notifies the adapter. This is useful when there is no data update but you want the progressbar to be updated.

## Persistent progress

If you want the progressbar to be persistent over multiple requests, you can give the name of a session namespace as fourth argument to the constructor. In that case, the progressbar will not notify the adapter within the constructor, but only when you call `update()` or `finish()`. Also the current value, the status text and the start time for ETA calculation will be fetched in the next request run again.

## Standard adapters

`Zend_ProgressBar` comes with the following three adapters: