plists

If you have ever gone through the ios filesystem you will find lots and lots of plists. Plists or property lists are basically xml files used to store information on the iphone.

A plist can store arrays, strings, nsdata, numbers, dates and nsdictionaries.

A plist has a basic structure, with one root element and everything under it.

Let us make a plist to save contacts (this may be a bad practice and is only for illustration purposes)
So to start with let the root element of our plist be an array which will hold all the contacts.
Each element of the array will be an nsdictionary with key value pairs as follows

• id - nsnumber
• name - nsstring
• phone - nsstring

It is a very simple structure and the iOS sdk offers a lot of convenience methods to load data from plists into arrays or dictionaries.

So during the first run of our program we would want to create a plist and save it to some locations, this location will most likely be your documents directory since it is automatically backed up by iTunes.

So first we need to get the path for the documents directory of our app, we get this through the following code 

NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);

NSString *writeReadPath = [[paths objectAtIndex:0] stringByAppendingPathComponent:@"contacts.plist"];

As you see the second line has the filename of the plist appended to the path of the documents directory we got, in this case we have named the file to be contacts.plist .

Now that we have got the path to our file, let us proceed to writing data on our file. If it is the first run of the app there is a possibility the file doesn't exist, to tackle this issue we add a few lines of code and create the plist with sample data

NSFileManager *fileManager = [NSFileManager defaultManager];

if (![fileManager fileExistsAtPath:writeReadPath]) {

     NSDictionary *contact1 = [NSDictionary dictionaryWithObjects: [NSArray arrayWithObjects:[NSNumber numberWithInt:1],@"John",@"1944232321",nil] forKeys:[NSArray arrayWithObjects:@"id",@"name",@"phone",nil]];

 NSDictionary *contact2 = [NSDictionary dictionaryWithObjects: [NSArray arrayWithObjects:[NSNumber numberWithInt:2],@"Steve",@"1944232421",nil] forKeys:[NSArray arrayWithObjects:@"id",@"name",@"phone",nil]];

 NSDictionary *contact3 = [NSDictionary dictionaryWithObjects: [NSArray arrayWithObjects:[NSNumber numberWithInt:3],@"Peter",@"1944132321",nil] forKeys:[NSArray arrayWithObjects:@"id",@"name",@"phone",nil]];

     NSArray *contacts = [NSArray arrayWithObjects:contact1,contact2,contact3,nil];

[contacts writeToFile:writeReadPath atomically:YES];

}

With this much of code we have managed to create a new plist file, add contacts to it, without even going to deep into file handling. Thanks to the convenience methods of nsarray and nsdictionary it becomes very easy to write data into plists. In future posts we will deal with editing and deleting items from a plist.