比对iOS版本号字符串大小

/**
 比对iOS版本号字符串大小

 @param versionA 只能是三段以内,英文字符"."分隔的,每段必须是非负整数的版本字符串
 @param versionB 只能是三段以内,英文字符"."分隔的,每段必须是非负整数的版本字符串
 @return 从A到B,结果 -1 升序, 0 相等, 1降序
 */
- (NSComparisonResult)versionNumberA:(NSString *)versionA compareVersionNumberB:(NSString *)versionB {
    NSArray *stringsA = [versionA componentsSeparatedByString:@"."];
    NSArray *stringsB = [versionB componentsSeparatedByString:@"."];
    NSComparisonResult result = NSOrderedSame;

    for (int i = 0; i < 3; i++) {
        NSInteger numberA = 0;
        NSInteger numberB = 0;
        if (i < stringsA.count) {
            numberA = [(NSString *)stringsA[i] integerValue];
        }
        
        if (i < stringsB.count) {
            numberB = [(NSString *)stringsB[i] integerValue];
        }
        
        if (numberA > numberB) {
            result = NSOrderedDescending;
            break;
        }else if (numberA < numberB){
            result = NSOrderedAscending;
            break;
        }
    }
    
    return result;
}