Cocoa Touch: are dynamically XML-defined views possible? - iphone

Question

first post. Been an iPhone developer intern for about five weeks now. I've read a lot of introductory Apress material, but please take it easy if I make some vocabulary violations. So far I've been able to find answers by searching and lurking. However I now have a task for which I can find little relevant information.
My iPhone application currently uses a rigid view hierarchy for selection of items. The MainViewController links to (err, Subviews?) a TableView for selecting any from a list of factories. Selecting a factory then loads a TableView for various statistics about that factory. The data to populate these tables loads from a remote JSON server by http.
I would like to have an XML definition of the view hierarchy on the remote server from which the application dynamically constructs the view structure. In this way the view structure is not hard-coded into the client (the iPhone ViewControllers/nibs) and offers more flexibility for reorganizing the content server-side.
Is this possible, and has anybody accomplished this? Most relevant answer was Dynamic UI in iphone, however upon reading I feel Apple's guide to Serializing/Archiving departs quickly from what I am trying to do. Can somebody explain its relevance or point to another resource?

Answer 1

Yes, it is entirely possible, and I (as well as others) have done something similar. Essentially, you will have to write a couple classes:
One is a Controller class to parse the XML to get the content you need upon download into a format you can use in a Model class. There are a number of OSS libraries out there, but don't use Cocoa's XML classes on the iPhone because they are just too slow when parsing. Be sure to double-check the license that comes with the OSS library so that you don't run afoul of GPL and the like.
The second class you'll need is one that will translate your model into a view hierarchy and place it on screen on the fly as the user moves through the content. This is to implement as individual steps, but the challenge is managing the content placement workflow.
The content noted in your question does depart a bit from the core task at hand but it can still be relevant to your interests. At the very least it may give you an idea on how to approach certain aspects of your project.

Answer 2

Here's a follow-up. I have accomplished what I wanted to do.
I have a ListViewController class and a Repository model/object. To parse XML, I used XPathQuery, Matt Gallagher's adaptation of libxml2 for Cocoa (http://cocoawithlove.com/2008/10/using-libxml2-for-parsing-and-xpath.html).
The ListViewController tracks the current XML path. When a cell in the table view is selected, the corresponding path is concatenated to the existing path. The ListViewController creates and pushes another instance of itself and PerformXMLPathQuery() returns an array to populate the table view cells. The Repository holds an NSMutableData object and an NSString with current path. Both are required for XPath Query:
NSArray *PerformXMLXPathQuery(NSData *document, NSString *query);
PerformXMLPathQuery does a lot of back work for you. This is how I used it to get what I wanted from the XML:
-(NSArray*)getListFromRepositoryWithPath:(NSString *)path {
// Get the nodes referred to by the path
NSArray *nodes = PerformXMLXPathQuery(repository.data, path);
// Build an array with the node names
NSMutableArray* sublist = [[NSMutableArray alloc] init];
for (NSDictionary* node in nodes) {
for (id key in node) {
if ([key isEqualToString:#"nodeChildArray"]) {
NSArray* subNodes = [node objectForKey:#"nodeChildArray"];
for (NSDictionary* subNode in subNodes) {
for (id subKey in node) {
if ([subKey isEqualToString:#"nodeName"]) {
[sublist addObject:[subNode objectForKey:subKey]];
}
}
}
}
}
// Ignore duplicate entries in the data
if ([sublist count] > 0) {
return [NSArray arrayWithArray:sublist];
}
}
return [NSArray arrayWithArray:sublist];
}
When a row is selected, I used didSelectRowAtIndexPath to prepare the next path and view controller:
- (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath {
NSString *nextXpathQueryString = [self.xpathQueryString copy];
// Build the path string for the next view's XML path query
if ([[nextXpathQueryString lastPathComponent] isEqualToString:#"*"]) {
nextXpathQueryString = [nextXpathQueryString stringByDeletingLastPathComponent];
nextXpathQueryString = [nextXpathQueryString stringByAppendingPathComponent:#ROOTNAME];
}
nextXpathQueryString = [nextXpathQueryString stringByAppendingPathComponent:[repository.currentListToDisplay objectAtIndex:indexPath.row]];
// Navigation logic. Create and push another view controller.
ListViewController *detail = [[ListViewController alloc] init];
// Populate the new ViewController
[detail setRepository:repository];
[detail setTitle:nextXpathQueryString];
[detail setXpathQueryString:nextXpathQueryString];
[nextXpathQueryString release];
UIBarButtonItem *doneButton = [[self navigationItem] rightBarButtonItem];
[[detail navigationItem] setRightBarButtonItem:doneButton animated:YES];
// Pass the selected object to the new view controller.
[self.navigationController pushViewController:detail animated:YES];
[detail release];
}
The cool thing is each instance of ListViewController keeps its own path string and content array. No fooling around with nested tree objects or pointers.
Essentially I have a flexible XML tree browser for the iPhone. Thanks Stack Overflow.