I have jut created a pattern in illustrator, I edited my design and added some new lines too whilst I was in the patten tool. When I was ready to save the pattern and press 'done' the below message popped up, if i press ok does this mean I will lose my design and if so how do I save all 'active content' so I am able to save the pattern into my swatches.
You drew additional lines? perhaps using the brush tool?
In that case Illustrator using a calligraphy brush. The message tells you it will be expanded, that is the path will be outlined and will become a shape. It won't be easily editable anymore. You can apply a default stroke instead. That won't be expanded.
Ok thankn you! I ended up saving the pattern as a symbol if that makes sense? Will I be able to still change colours of the pattern now its a symbol?
You can always edit a symbol.
You could also use Edit > Edit colors > Recolor artwork on aplaced symbol instance
Monika is right, but I want to add to this thread. Another way to save your linework with the live brush applied (before it gets expanded) is to copy it to your clipboard and paste on the artboard when you leave Pattern mode. Making a symbol out of the art saves it to your symbols panel and you can get it there and edit it or break the link and use it as an object. But the symbol content that is inside your pattern mode pattern will be expanded on exit, just like any other "live" content.
I think the symbol workaround you described is a great idea for saving your original live art apart from your pattern fill when you are drawing in Pattern Mode and you get that warning. I just want to clarify that it does not protect the art from getting expanded 'within' the pattern fill. But it does create a copy of the live art that you can change the brushstroke on later. So for pattern designers, I always recommend keeping copies of your art/motifs outside of pattern mode so you retain all of it's editability should you need to change a brushstroke or thickness later.