将对象移动到另一个索引

将蓝色移动到数组的开头：

NSMutableArray *myColors = [NSMutableArray arrayWithObjects: @"Red", @"Green", @"Blue", @"Yellow", nil];

NSUInteger fromIndex = 2;
NSUInteger toIndex = 0;

id blue = [[[self.array objectAtIndex:fromIndex] retain] autorelease];
[self.array removeObjectAtIndex:fromIndex];
[self.array insertObject:blue atIndex:toIndex];

myColors 现在是 [@"Blue", @"Red", @"Green", @"Yellow"]。