Filtering Using a Custom Array Controller
This article explains how to use a search field and custom array controller to filter a collection of objects. Although you typically use a search field in conjunction with a table view to implement this style of interface, the tasks discussed in this article are not limited to these components.
Overriding arrangeObjects:
The arrangeObjects:
method sorts the content of the array controller using the current sort descriptors. To restrict the displayed content to a subset of the content you must override arrangeObjects:
, create a new array containing the subset, and then call the superclass’s implementation of arrangeObjects:
to provide any appropriate sorting.
The arrangeObjects:
implementation in Listing 1 performs an anchored search of the title property. In an anchored search, only those objects whose title property matches searchString
are added to the returned array.
Listing 1 Filtering implementation of arrangeObjects:
- (NSArray *)arrangeObjects:(NSArray *)objects { |
if (searchString == nil) { |
return [super arrangeObjects:objects]; |
} |
NSMutableArray *filteredObjects = [NSMutableArray arrayWithCapacity:[objects count]]; |
NSEnumerator *objectsEnumerator = [objects objectEnumerator]; |
id item; |
while (item = [objectsEnumerator nextObject]) { |
if ([[item valueForKeyPath:@"title"] rangeOfString:searchString options:NSAnchoredSearch].location != NSNotFound) { |
[filteredObjects addObject:item]; |
} |
} |
return [super arrangeObjects:filteredObjects]; |
} |
Updating the Search String
You implement the search:
action method to invoke rearrangeObjects
, which triggers the invocation of the arrangeObjects:
method.
Listing 2 shows an implementation of a search: action. The searchString
is set to the string value of the sender
object, and rearrangeObjects
is called.
Listing 2 Updating searchString
- (void)search:(id)sender { |
// set the search string by getting the stringValue |
// from the sender |
[self setSearchString:[sender stringValue]]; |
[self rearrangeObjects]; |
} |
- (void)setSearchString:(NSString *)aString |
{ |
[aString retain]; |
[searchString release]; |
searchString=aString; |
} |
@end |
The search:
action is invoked by an NSSearchField. The target of the search field is set to the array controller, and the action to the search:
method. The search field should be configured so that it does not send the whole string as it changes. Turning this option off causes the search:
method to be invoked each time that a keystroke occurs in the search field.
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