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];

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.