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Zero, one and Many

When learning to program you are taught to be careful when dealing with edge cases. It's quite typical to make errors at the low ends and extremes of your software. The same is true from a user interface standpoint. When designing software programmers often forget to check the edge cases of Zero, One and Many. I'm not talking about the actual code in the software but rather the user interface.

Zero is a special case:
Most interfaces deal with lists or collections. You have collections of emails, photos, favorites, fonts, and more. Often times people forget that you have to deal with the list when it has no items in it. The thing that many programmers do is to leave the list or collection blank. To the programmer it simply looks like an empty list. To a user of your software it looks like a big white box that you can't type in. When dealing with lists and collections make sure you deal with the case where a list has zero items. Make it intuitive how to add a new item. Use that white space to explain what the user should do and what types of items the list will contain.

One is a special case:
Modern computers have user interfaces that are equipped to handle collections of things even when it's typical to only have one. For example most software can support multiple sound cards, multiple monitors, multiple home addresses, multiple fax numbers and multiple emails. User interfaces are often built to handle these collections but they treat the first item in the collection the same as the second. Programs need to make sure that in situations where the first item may carry more importance then the second that adding the second item encourages you to replace your original entry. Did the user want to create a new profile or did they simply want to alter the original?

Many is a special case:
When dealing with a collection it's often easy to forget that the collection can get very large. It may be OK to select an item from a drop-down list when there are 10-20 items but the user interfaces will become unmanageable when the drop-down has 1000 items. If your list deals with many items make sure that it's reasonable to use the UI when the list gets big. Many Font drop-downs fail terribly with designers who install 100's of fonts. Many network dialogs don't work well because users are on corporate networks with 1000's of computers. If your lists can grow make sure your UI can adjust to handle it.

This post is licensed under CC BY 4.0 by the author.