write into plist file using NSDictionary object - iphone

Question

Sorry I saw similar questions but they don't seem to have some full answers for me. And i try to put it in order so that people will not hate me or my poor english.
I am working with Xcode 4.2 with storyboard and ARC
I can read from my plist file. My task is simply to write back the updated value(s) to my plist file.
My plist is contain in "supporting files" sub folder of the main folder (where story-board is things goes). the file is call Global.plist and GlobalValue2 is a element of the file type string.
So the read file part looks like this
NSString *plistfile = [[NSBundle mainBundle] pathForResource:#"Global" ofType:#"plist"];
NSDictionary *dict = [NSDictionary dictionaryWithContentsOfFile:plistfile];
FirstValueTextBox.text = [[dict valueForKey:#"GlobalValue1"] stringValue];
learn it from some handy youtube video works just fine. updates the value to my text box.
The real problem comes in when I write back my plist file. When i try the following
NSString *plistfile = [[NSBundle mainBundle] pathForResource:#"Global" ofType:#"plist"];
NSMutableDictionary *dict = [NSMutableDictionary
dictionaryWithContentsOfFile:plistfile];
[dict setValue:#"ABC" forKey:#"GlobalValue2"];
SecondValueTextBox.text = [dict valueForKey:#"GlobalValue2"];
[dict writeToFile:plistfile atomically:YES];
the result is I really saw a updated value pop up on the second text box, but the plist file remain unchanged.
The following are the break down of my questions and my guess for the problem
I try to use NSDictionary(not NSMutableDictionary) and call setValue (crash in runtime)
my guess: NSDictionary object itself is readonly so it crash me when i say add value. But why don't it error me when in coding time? if the object is readonly
I use NSMutableDictionary can call setValue. it doesn't crash me and when i call the updated value at "SecondValueTextBox.text = [dict valueForKey:#"GlobalValue2"];" it really return me the updated value. but the content inside of the plist file is not changed. Which is the result I have right now.
my guess: after some search here and there I think "supporting files" is read only too. pure guess did see anyone directly talk about it.
I did try to move on a little more and some people talks about a "document folder" in Xcode that is a read and write place. I think people also talk about write a code to access that folder. Can someone show me the code here.
My last question, can I hook up my Xcode to that "document folder" or where can i see it(the real file folder structure is different from inside Xcode I think). So that i can see and edit my plist file for testing, and i can see the real result without using codes and stuff
I will be much appreciated if people can tell me my guess is right or wrong and the answer to my 3 and 4 question.

Answer 1

In order for your changes to be persisted in your plist, you would indeed need ot copy it from the resource bundle to the documents dirtectory on launch of the application, then use the plist in the documents to read and write.
Here is how you can copy the file:
NSFileManager *fileManager = [NSFileManager defaultManager];
NSError *error;
NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
NSString *documentsDirectory = [paths objectAtIndex:0];
NSString *plistPath = [documentsDirectory stringByAppendingPathComponent:#"Global.plist"];
if ([fileManager fileExistsAtPath:plistPath] == NO) {
NSString *resourcePath = [[NSBundle mainBundle] pathForResource:#"Global" ofType:#"plist"];
[fileManager copyItemAtPath:resourcePath toPath:plistPath error:&error];
}