WPF - change global font size at runtime

Question

I need to add one functionality to my simple application - to allow user to change font size for whole aplication. Is it easy to do? Can you give me any hint how to start? It's required to have only 3 predefined font sizes but the first and only solution which came to my mind is to create 3 different themes. Is it possible to make it simplier?

Answer 1

Luckily, FontSize uses Property Value Inheritance. That means that so long as don't override it, FontSize will be automatically propagated to all child text elements. As a result, you can set a single:

<Window FontSize="10" ...>

and it will apply to all text elements in that window that don't have a font size. To change it in code is simple as well:

this.FontSize = 20;

in the code-behind of the window will change all unspecified font sizes on the fly. This also works for things that don't seem to support font size:

<Grid TextElement.FontSize="15" ...>

The same is true for the other text properties you mentioned.

Answer 2

Application.Current.MainWindow.FontSize = 12;