Is it possible to parse an NSInputStream using SBJ

问题:

I am trying to a read JSON file containing contact info objects consisting of NSString types and NSMutableArrays. Currently, I am using NSData to read the whole file and then parsing through it. I have utilised Stig's example as mentioned here: SBJson4Parser Example

   SBJson4ValueBlock block = ^(id obj, BOOL *stop) {
   NSLog(@"Found: %@", @([obj isKindOfClass:[NSDictionary class]]));
    //contactsData *contact = obj;
    NSDictionary *contact = obj;
    NSLog(@"Contact: %@",contact);
   /* NSString *fName, *lName;
    fName = [contact objectForKey:@"mFirstName"];
     lName = [contact objectForKey:@"mLastName"];
    NSLog(@"First Name: %@",fName);
    NSLog(@"Last Name: %@",lName);
    */
};

SBJson4ErrorBlock eh = ^(NSError* err){
    NSLog(@"Oops: %@",error);
};
NSLog(@"Parse work");
id parser = [SBJson4Parser multiRootParserWithBlock:block
                                       errorHandler:eh];
//uint8_t buf[1024];
//unsigned int len = 0;
NSLog(@"Trying to push stream to data");
//[inputStream read:buf maxLength:len];
NSData *data = [NSData dataWithContentsOfFile:filePath options:NSUTF8StringEncoding error:NULL];
//id data = [json da:NSUTF8StringEncoding];
SBJson4ParserStatus status = [parser parse:data];

NSLog(@"Status: %u",status);

These days people seem to have hundreds or even thousands of contacts, thanks to social networks. Will this lead to a larger memory footprint on an iOS device ? If so, how do I parse a single object from a stream ? If I have to use a delegate, an example would be greatly appreciated.

Please note that I am new to the world of iOS development as well as Objective-C.

The structure of the json file in question:
{
  "mAddresses": [
  ],
  "mContactPhoto": "",
  "mDisplayName": ",tarun,,,,israni,,", 
  "mPhoneNumberList": [
    {
      "mLabel": "_$!<Home>!$_",
      "mNumber": "[phone]",
      "mType": 1
    }
  ]
}{
  "mAddresses": [
  ],
  "mContactPhoto": "",
  "mDisplayName": ",Sumit,,,,Kumar,,",
  "mPhoneNumberList": [
    {
      "mLabel": "_$!<Home>!$_",
      "mNumber": "[phone]",
      "mType": 1
    }
  ]
}

回答1:

Your solution looks like it should work to me. If your file so big that you don't want to hold it all in memory, i.e. you want to avoid this line:

NSData *data = [NSData dataWithContentsOfFile:filePath options:NSUTF8StringEncoding error:NULL];

then you can use an NSInputStream (untested, but hopefully you get the gist):

id parser = [SBJson4Parser multiRootParserWithBlock:block
                                       errorHandler:eh];

id is = [NSInputStream inputStreamWithFileAtPath:filePath];
[is open];

// buffer to read from the input stream
uint8_t buf[1024];

// read from input stream until empty, or an error;
// better error handling is left as an exercise for the reader
while (0 > [is read:buffer maxLength: sizeof buffer]) {
    SBJson4ParserStatus status = [parser parse:data];
    NSLog(@"Status: %u",status);
    // handle parser errors here
}
[is close];

However, you still have to read and parse the whole file to guarantee that you find a particular contact. There is no way to read just a specific contact this way. If that is something you do often, you may want to store your contacts a different way that supports that scenario better. One way would be to use e.g. SQLLite.