MrDML

        /**
         * 随机字符串
         */
        private static final char[] CHARS = new char[] {'F', 'L', 'G', 'W', '5', 'X', 'C', '3',
            '9', 'Z', 'M', '6', '7', 'Y', 'R', 'T', '2', 'H', 'S', '8', 'D', 'V', 'E', 'J', '4', 'K',
            'Q', 'P', 'U', 'A', 'N', 'B'};

        private final static int CHARS_LENGTH = 32;
        /**
         * 邀请码长度

MrDML

/*
 * Adds the serialNumber property to the UIDevice class
 *
 * The implementation uses undocumented (for iOS) IOKit functions,
 * so handle with caution and be prepared for nil.
 */

#import <UIKit/UIDevice.h>

@interface UIDevice (serialNumber)