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i’ve written code select random color nsarray, how can make same color doesn’t selected 2 times in row? appreciated.
+ (nsarray *)colors { static nsarray *colors = nil; static dispatch_once_t once; dispatch_once(&once, ^{ colors = @[ //green [uicolor colorwithred:88.0/255.0 green:195.0/255.0 blue:98.0/255.0 alpha:1], //yellow [uicolor colorwithred:246.0/255.0 green:194.0/255.0 blue:48.0/255.0 alpha:1], //orange [uicolor colorwithred:236.0/255.0 green:135.0/255.0 blue:40.0/255.0 alpha:1], //red [uicolor colorwithred:226.0/255.0 green:51.0/255.0 blue:40.0/255.0 alpha:1], //blue [uicolor colorwithred:59.0/255.0 green:156.0/255.0 blue:218.0/255.0 alpha:1], //violet [uicolor colorwithred:138.0/255.0 green:70.0/255.0 blue:165.0/255.0 alpha:1], ]; }); return colours; } _selectedcolor = [colors objectatindex: arc4random() % [colors count]];
shuffle array of colors , return elements in order. when reach end, reshuffle , start over. make sure don't allow last element become first element avoid returning same element twice in row. guarantees use each color equal number of times.
@implementation uicolor (random) static uicolor *rgb(cgfloat red, cgfloat green, cgfloat blue) { return [uicolor colorwithred:red/255 green:green/255 blue:blue/255 alpha:1]; } void shuffle(nsmutablearray *array) { // based on http://stackoverflow.com/a/56656/77567 nsuinteger count = array.count; if (count < 2) return; // don't allow last element become first, don't same color twice in row. [array exchangeobjectatindex:0 withobjectatindex:arc4random_uniform(count - 1)]; (nsuinteger = 1; < count - 1; ++i) { nsinteger remainingcount = count - i; nsinteger exchangeindex = + arc4random_uniform((u_int32_t )remainingcount); [array exchangeobjectatindex:i withobjectatindex:exchangeindex]; } } + (instancetype)randomcolor { static dispatch_once_t once; static nsmutablearray *colors; static int nextcolorindex; static dispatch_queue_t queue; // serializes access colors , nextcolorindex dispatch_once(&once, ^{ colors = @[ rgb(88, 195, 98), // green rgb(246, 194, 48), // yellow rgb(236, 135, 40), // orange rgb(226, 51, 40), // red rgb(59, 156, 218), // blue rgb(138, 70, 165), // violet ].mutablecopy; shuffle(colors); queue = dispatch_queue_create("uicolor+random.randomcolor", 0); }); __block uicolor *color; dispatch_sync(queue, ^{ color = colors[nextcolorindex++]; if (nextcolorindex == colors.count) { nextcolorindex = 0; shuffle(colors); } }); return color; } @end 
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