Maximum number of entries in a ListBox_问答_开发者

What is the maximum number o开发者_运维技巧f entries a simple ListBox (ComboBox) should contain? There are fifty states in the US - is 50 too many? There are over 270 countries and territories in the world - is 270 too many?

When should a ListBox include search or type-ahead capabilities? When should the designer consider something other than a ListBox?

Do you have any links to cool widgets that help a user select from one of many options?

Thank you in advance.

If the user knows the precise value she or he wants from a well-sorted list with type-ahead, then over 1000 items is okay. Seriously. Try it yourself: Do a search of your hard drive that yields 1000 or so files and see how hard it is to scroll or type-ahead to a file you know is there.

What matters more than the raw number of items is the ratio of items in the list to the items visible in your scrollable pane, whether you’re talking about a list box or the dropdown portion of a combo box. You want at least 5% of your items visible at a time. So for 1000 items, you need a pane about 800 pixels high (at 16 pixels per line). That sets about 1000 as the limit given typical low-end desktop monitor sizes. If you’re talking about users with laptops using a web site, then you’ve only got about 560 pixels (allowing for browser controls and such), so now you’re looking at 700 items. Still a lot. We’re assuming a proper scrollable list where the list scrolls instantly with dragging the slider.

I only see a need for filtering/search controls (versus type ahead alone) when the number of items is more like 1000s than 100s, although you need to make exceptions for special cases (e.g., when the user doesn't really know what s/he precisely wants and needs to explore the alternatives on various criteria, or when there's a large number of items all beginning with the same 9 letters).

Always have type-ahead. There no reason not to, and even with a small the number of items, it benefits users using the keyboard only rather than the mouse (very common for data entry). Treat it as a standard. You don't want users having to guess if you chose to have type-ahead or not for a given field ("Does he think 10 items is enough? Does he ever have it?"), so just have it all the time.

I would suggest that an autocompleter be used whenever a list is larger than about 50 items.

Talking about usability here, one thing hasn't been mentioned.

For the list of countries in particular, if you're including the full list of 200-whatever it's often a good idea to list the most popular few at the very top of the list, based on your anticipated market.

It might seem counter-intuitive since programmers like nice, neatly sorted lists of things (myself included), but no one likes scrolling to near the bottom of the list to find "USA". Or, always seeing Cambodia, Cameroon, and then Canada. I couldn't show where Cambodia or Cameroon are on a map (though my geography skills are below-average), but the names have been seared into my mind by these lists.

Remember that not all users use, or even know about, auto-complete or even typing what they want in a list. It's certainly an excellent aid, but it should not be relied upon.

I would think that 270 is too many and would be a bad experience. I would think about grouping countries into regions/continents and keep the list down. UPS/Fedex/Canon all do this.

I'm not sure of a magic number, but I think that looking at 51 states[50 + D.C.] is common enough that it's acceptable. I would imagine that there would be a similar track for the other Countries as well.

For instance: France has 100 departments are grouped into 22 metropolitan and four overseas regions.

For more than about 50-ish (and really, even that is pushing it IMO) I'd much rather have a simple text box with auto-complete (think Google search suggest) than a drop-list.

I'm not american, nor have I developed for the american market yet, but I've always found those state dropdowns horrible.

Isn't it possible to have the user enter the Zip code and to look up the state automatically?