Question

I am trying to replace placeholders in a text file, with html elements built from the placeholder content.

So for example I have a placeholder such as {Image, picture.jpg, Centre, Picture Info}

I want to convert this into:

<img src="urltopicture\picture.jpg" alt="Picture Info" class="quipImgCentre"></img>

I’m looking to use a Regex to identify all placeholders, then working backwards through the document convert and replace each one in turn.

The Regex {.*} works where there is only one placeholder on a line, but not if more than one – in the text below, it will return as one long placeholder, everything from the first opening “{” to the last “}”.

 Aenean non felis at est gravida tincidunt. {Link, news.bbc.co.uk, popup, 500, 800} Donec non diam a mauris vestibulum condimentum eu vitae mi! Aenean sed elit libero, id mollis felis! {Image, ServiceTile.jpg, Left}

Also – if anyone has a neater way of performing this placeholder replacement I’d love to hear it.

Answer 1

Repeat this part for each of your Placeholders:

Regex PlaceholderExpander = new Regex(@"\{Image, ([^,]+), ([^,]+)(?:, ([^}]+))?\}");
string Expanded = PlaceholderExpander.Replace(YourHtmlStringWithPlaceholders, "<img src='$1' alt='$3' class='quipImg$2'></img>");

The [^,] means “any character but a ,“, so that stops before the next , in spite of the greedy + quantifier. It’s a trick for processing speed. A more obvious alternative would be using a lazy (a.k.a. ungreedy, reluctant) quantifier.

The (?:…) is a non-capturing group – it can not be backreferenced with something like $3. I used it to encompass the part belonging to the optional last parameter – it is made optional with the last ?.

I made the last parameter optional now, so it supports both

{Image, picture.jpg, Centre, Picture Info}

and

{Image, ServiceTile.jpg, Left}

the latter resulting in

<img src='ServiceTile.jpg' alt='' class='quipImgLeft'></img>

I have tested this in http://rextester.com/rundotnet with this code:

string YourHtmlStringWithPlaceholders = "Aenean {Image, picture.jpg, Centre, Picture Info} non felis at est gravida tincidunt. {Link, news.bbc.co.uk, popup, 500, 800} Donec non diam a mauris vestibulum condimentum eu vitae mi! Aenean sed elit libero, id mollis felis! {Image, ServiceTile.jpg, Left}";

Regex PlaceholderExpander = new Regex(@"\{Image, ([^,]+), ([^,]+)(?:, ([^}]+))?\}");
string Expanded = PlaceholderExpander.Replace(YourHtmlStringWithPlaceholders,"<img src='$1' alt='$3' class='quipImg$2'></img>");

Console.WriteLine(Expanded);