Abstracting UI data formatting

Question

Hi,

I've got some entities which have decimal properties on them. These entities' properties are displayed in multiple places throughout my UI.

Currently I'm finding myself doing:

litWeight.Text = person.Weight.ToString("0.00");

all over the place. Now I know for a fact that in several instances, and am suspicious of many others that the client is likely to want the values to 3d.p. in the future.

Is there some pattern I can employ to handle the formatting of this Weight property (and other properties; not just decimals, perhaps dates etc.) so that I can have this formatting in a single place?

I know could use a formatstring in the webconfig, or write some extension methods in the UI but these don't seem very elegant solutions.

It would be nice to have some formatting objects which are tied to my entities, so its inherently obvious which formatter to use.

Thanks,

Andrew

Answer 1

The simplest solution would be to make a utility class with static methods that appropriately format different types of values and call them. For example:

litWeight.Text = Utility.FormatWeight(person.Weight);

Answer 2

Can you not add a method to the entities for formatting themeslves? Then each object can delegate to a 'strategy' object to do the actual formatting.

A reason for this is both to be able to change the decimal places etc, but also to allow things like internationalisation - decimal formatting is locale-dependent; some countries use decimal commas instead of points, or group digits in sets other than threes etc.

EDIT: The comment was this puts presentation code in the domain layer. True, so apply the standard fix for all design problems; add one more layer of indirection :)

You may not want to have the full MVC, but the concept of View and Model still seem appropriate. Perhaps, for each entity, define a View class, so PersonView which keeps a reference to a Person object and has properties called format_weight etc for each property of Person that is of interest? It should still use a Strategy pattern for the actual formatting.

So your example would be

PersonView pv = new PersonView(person)

litWeight.Text = pv.format_weight();

(please excuse syntactical errors, I don't speak C#)

If you want, you could make PersonView drop in replacement for Person, either by reimplementing the methods/properties and delgating to the referenced Person, or by inheriting from Person when making PersonView?

Answer 3

You could create a very basic user control - deriving from label or similar - that is responsible purely for displaying a weight string so you then have:

weightValue.DisplayValue(person.Weight);

and the setter formats the decimal as required. If this is used whenever you display a weight then you only have to alter the user control to change all displays of weight.

A basic version could be:

public void DisplayValue(decimal weight)
{
    this.Text = weight.ToString("0.00");
}