获取URL的指定参数对应值

+ (NSString *) paramValueOfUrl:(NSString *) url withParam:(NSString *) param{

NSError *error;
NSString *regTags=[[NSString alloc] initWithFormat:@"(^|&|\\?)+%@=+([^&]*)(&|$)",param];
NSRegularExpression *regex = [NSRegularExpression regularExpressionWithPattern:regTags
options:NSRegularExpressionCaseInsensitive
error:&error];

// 执行匹配的过程
NSArray *matches = [regex matchesInString:url
options:0
range:NSMakeRange(0, [url length])];
for (NSTextCheckingResult *match in matches) {
NSString *tagValue = [url substringWithRange:[match rangeAtIndex:2]];  // 分组2所对应的串
return tagValue;
}
return nil;
}