用法：
//使用颜色作为背景
var pressed = "#333333"
var selected = "#333333"
var normal = "#888888"
var b = i.nuibs(pressed, selected, normal)

//使用图像作为背景
var pressed = "%a.png"
var selected = "%a.png"
var normal = "%b.png"
var b = i.nuibs(pressed, selected, normal)

//使用渐变颜色作为背景
.配置选中状态背景
var a = 0
var b = 0
var c = "#255779|#3e7492|#a6c0cd"
var d = "0"
var e = "topbottom"
var pressed = i.ngde(a, b, c, d, e)

.配置正常状态背景
var a = 0
var b = 0
var c = "#255779|#3e7492|#a6c0cd"
var d = "0"
var e = "rightleft"
var normal = i.ngde(a, b, c, d, e)

var selected = pressed

var b = i.nuibs(pressed, selected, normal)

说明：
输入按下背景，输入选中背景，正常状态背景。