qgis/Quantum-GIS — pull request #51 by NathanW2 (2011-10-17 13:58:24+00:00)
Title: Add support for expression based labels and a new expression string builder widget/dialog.

So after a long while I thought it was time to submit a pull request on this one.

Adds support to use expression as a label eg 'Dia=' || Diameter || 'mm' will render Dia=300mm as a label.

![Label example](http://dl.dropbox.com/u/6170988/label.png)

Also adds a new reusable expression string building widget. This widget is used to build the label expression string currently but is aimed to replace the field calculator, query builder and any other dialog that requires an expression string.

![New expression dialog](http://dl.dropbox.com/u/6170988/Expression%20string%20builder_015.png)

![Invalid expression](http://dl.dropbox.com/u/6170988/Expression%20string%20builder_invalid.png)

### Features of the new widget

* More future expandable function list using tree widget and groups.
* Real time function search
* Real time expression validation.
* Real time expression output preview
* Help on selected function ( not all help is written yet).
* Load sample 10 or all unique values from field using right click menu.
* Reusable

## Still Remaining
* Write help for the remaining functions.