I have an NSData that was created by using NSKeyedArchiver. Is there a way to iterate over all the values inside it? It must somehow be possible to get all the keys that were stored in it when using +[NSKeyedUnarchiver unarchiveObjectWithData:].
Thanks
A NSKeyedArchived file "simply" is a property list. You would need to find out the structure of that plist, though.
I found the source code of Cocotron very helpful one day, as I tried to decode some NSKeyedUnarchived data: http://code.google.com/p/cocotron/source/browse/Foundation/NSKeyedArchiving/NSKeyedUnarchiver.m (Maybe look at line 39 (initForReadingWithData:) which is called by unarchiveObjectWithData: (line #164)).
Maybe you can find out more about the archived objects that way.
Related
I am trying to log excretions in a text file in JSON format. Whole file is like a JSON object (an array of customeModle Class).
It works fine for first time but for next time when I go to log into the file I have to read it then add the new object into the array then delete previous and save it again and obviously it is not a good way to log errors.
Problems
Suppose there are many errors are getting logged at a single point of time and all are reading and appending the array then writing it back to the log file then many error won't be logged for sure.
It is consuming and wasting to much cpu and ram energy.
Please suggest a way to append new objects in the existing file without overwriting it.
Many thanks for your help you may offer.
Per Apple Documentation, you can open a file (output stream) in append mode.
Given you hold a reference to file output stream outStream, you can use below method to append data:
[NSJsonSerialization writeJSONObject:myNewObject toStream:outStream options:1 error:&error]
However, I would personally use the option you are already doing - read the data in mutable object, modify and then use NSJSONSerialization to convert it back to data again. Finally, save that data to disk - replacing the original. As this keeps JSON structure intact.
I've been working on this for a few days now. Searched Stackoverflow and other sites for solutions but none of them appear to work. Most of the postings I've found are quite old (before 2013) so I'm thinking this is not the right way to do this.
I thought this would work:
[localMutableDictionary addEntriesFromDictionary:deviceDictionary];
localMutableDictionary remains null
I've worked around this using an array of integers instead of a mutable dictionary. But that doesn't give me the right result when I add the array to an NSDictionary for subsequent processing with NSJSONSerialisation. Values from my array don't get double quote marks around them. The json receiver / parser is expecting values in quotes (runs with json produced in VB code for a similar app). I can use an alternative parser to work around this, but I would rather get a clean solution.
This is probably a case of there being a simple syntax that I haven't managed to find, or that I'm just using an out-of-date style. Or I may just be adding my array to the NSDictionary "the wrong way". A solution for either method would work for me - thank you.
I have seen How to read/write from/to file using golang? and http://golang.org/pkg/os/#File.Write but could not get answer.
Is there a way, I can directly write an array of float/int to a file. Or do I have to change it to byte/string to write it. Thanks.
You can use the functions in the encoding/binary package for this purpose.
As far as writing an entire array at once goes, there are no functions for this. You will have to iterate the array and write each element individually. Ideally, you should prefix these elements with a single integer, denoting the length of the array.
If you want a higher level solution, you can try the encoding/gob package:
Package gob manages streams of gobs - binary values exchanged between an Encoder (transmitter) and a Decoder (receiver). A typical use is transporting arguments and results of remote procedure calls (RPCs) such as those provided by package "rpc".
I am making an app that lets the user draw on the screen in different colors and brush sizes. I am storing the info about each drawn path in a JSON file once it has been drawn to keep it out of memory. Right now I have it parsing all existing paths, then adding the new one in and writing it all back out again. I want it to simply append the new data into the JSON file without having to read it in and parse it first, that will make it so only one path is ever in memory at a time.
I am using SBJSON, the JSONWriter has a few append functions but I think you need to have the JSON string to append it to first, not the file, meaning I would have to read in the file anyway. Is there a way to do this without reading in the file at all? I know exactly how the data is structured.
It's possible, but you have to cheat a little. You can just create a stand-alone JSON document per path, and append that to the file. So you'll have something like this in your file:
{"name":"path1", "from": [0,3], "to":[3, 9]}
{"name":"path2", "from": [0,3], "to":[3, 9]}
{"name":"path3", "from": [0,3], "to":[3, 9]}
Note that this is not ONE JSON document but THREE. Handily, however, SBJsonStreamParser supports reading multiple JSON documents in one go. Set the supportMultipleDocuments property and plug it into a SBJsonStreamParserAdapter, and off you go. This also has the benefit that if you have many, many paths in your file as you can start drawing before you're finished reading the whole file. (Because you get a callback for each path.)
You can see some information on the use case here.
I'm pretty sure its not possible...what I ended up doing was reading in the JSON file as a string then instead of wasting memory changing all that into Dictionaries and Arrays, I just looked for an instance of part of the string (ex: i wanted to insert something before the string "], "texts"" showed up) where I wanted to insert data and inserted it there and wrote it back out to file.
As far as I can tell this is the best solution.
I am creating a syntax highlighting engine. My need is very specific. Keywords will be associated to their respective attribute array via a pointer. The data structure will look something like:
dict = {
"printf": keyword_attr_ptr
, "sprintf": keyword_attr_ptr
, "#import": special_attr_ptr
, "string": lib_attr_ptr
}
The look-up needs to be very fast as I will be iterating over this list every keypress.
I'm asking this question because I can not find any good documentation regarding how NSDictionary caches (if it does) and looks up values by its keys (does it use a map? a hashmap?). Can I rely on NSDictionary to be optimized to search for keys by strings?
When I was doing something similar a long while ago I used the MFC CMap function with very good results. NSDictionary appears to be the equivalent to CMap but the key type isn't specified and the NSDictionary clearly states that a key can be any type of object. I just want to make sure I can rely on it to return the results extremely fast before I put a lot of energy into this problem.
UPDATE 1
After a day of research, I ask the question on SO and I find the answer immediately after... go figure.
This is the documentation related to Dictionaries:
https://developer.apple.com/library/mac/#documentation/Cocoa/Conceptual/Collections/Articles/Dictionaries.html
It uses a hash table to manage its storage. I guess the short answer is that its almost equivalent to CMap.