358	CHAPTER 10: Storyboards

Figure 10-3. The summary of the Simple Storyboard target

Dynamic Prototype Cells

As you may recall from Chapter 8, iOS 5 lets you create a nib file containing a UITableViewCell and whatever objects you want the cell to contain, and use a unique identifier to register that cell with the table view. Then, at runtime, you can ask the table view to give you a cell based on an identifier, and if the identifier matches your earlier registration, that’s what you’ll get.

With storyboards, this concept is cranked up a notch. Now, instead of creating separate nib files for each type of cell, you can create them all in a single storyboard, directly inside the table view where they will be presented! Let’s see how this is done.

Dynamic Table Content, Storyboard-Style

We’re going to make a controller that displays a list of items. Depending on the content of each item, we’ll display them with a fairly plain style or with a more eye-catching style to alert the users that they need to pay special attention to the item. Just to make things concrete, let’s imagine these items are to-do list entries, and we want to alert the users to entries that are urgent. To keep things simple, we’ll use a plain UITableViewCell for each displayable cell instead of defining any cell subclasses. For more complicated displays in a real app, you would probably want to create your own cell subclasses to use here. In either case, the setup and workflow are the same.

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Since you’ve already made a new project and hardly changed a thing, let’s stick with our Simple Storyboard project. Make a new class in the Xcode project window. Select File

New New File…, then in the Cocoa Touch section choose UIViewController subclass, and then click Next. Name the class BIDTaskListController, and select UITableViewController from the Subclass of popup. Click to turn off the checkbox for creating a new XIB file, since we are going to work within the storyboard instead.

After the class files are created, switch back to MainStoryboard.storyboard, where we’ll put an instance of our new controller (and, of course, a view to match). Grab a Table View Controller from the object library and pull it out into the editing area, placing it to the right of the controller you started with. It should now look something like Figure 10-4. You’ll likely see a warning, complaining that “prototype table cells must have reused identifiers,” but no worries; we’ll address this soon.

Figure 10-4. The new table view controller, just to the right of the original view controller

Now we need to configure the table view controller to be an instance of our controller class, not the default UITableViewController. Select the newly inserted table view controller, making sure you’re selecting the controller itself, not the table view it contains. The easiest way to do this is to click the icon bar below the table view or to click the Table View Controller row in the dock. You’ll know you’ve got it when both the table view and the icon bar are outlined in blue. Open the identity inspector, and change the controller’s class to BIDTaskListController so that the table view knows where to get its data.

Editing Prototype Cells

You’ll see that the table view has a one-item group at the top labeled Prototype Cells. This is where you can graphically lay out cells however you like, and give them unique identifiers for later retrieval in your code.

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360 CHAPTER 10: Storyboards

Start by selecting the one blank cell that is already there and opening the attributes inspector. Set this cell’s Identifier to plainCell, and then drag a Label from the object library directly into the cell itself. Drag the label over near the left edge so that the blue guideline pops up, and then resize its width, dragging the right edge out toward the right edge of the cell until the blue guideline appears over there. Finally, with the label selected, use the object inspector to set its tag to 1 (see Figure 10-5). This will let us find the label from within our code.

Figure 10-5. With the label selected, we used the attributes inspector to change the label’s tag to 1. Note that the Tag field is in the View section toward the bottom of the inspector. The cursor is pointing at the field.

Now, select the table view cell itself (not the label it contains), and choose Edit Duplicate. This places a new copy of the cell directly below the original.

NOTE: Selecting the table view cell can be tricky. In the version of Xcode we used when we wrote this chapter, we needed to actually click the table cell in order to be able to duplicate it.

Selecting the cell in the dock was not enough. Likely this will change over time.

With the new cell selected, use the object inspector to set its identifier to attentionCell. Then select the new cell’s label, and use the attribute inspector to change the label’s

Text Color field to red, and set its Font to System Bold.

Now we have two prototype cells that are ready to use in this table view. Before we implement the code to populate this table, we need to make one more change to the storyboard. Remember that big, floating arrow that points to our original view? Drag that over to point to our new view instead. Save your storyboard.

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Good Old Table View Data Source

Head over to BIDTaskListController.m, where we’re going to add some code to populate our table. This is mostly pretty standard table view stuff that you’ve seen plenty of times before, so we’re going to whizz through it and skip explanations for all but the newest bits. Start by adding these bold lines near the top of the file:

#import "BIDTaskListController.h"

@interface BIDTaskListController ()

@property (strong, nonatomic) NSArray *tasks; @end

@implementation BIDTaskListController

@synthesize tasks;

This just sets up a property to contain a list of items we want to show.

Now, insert the following code in viewDidLoad to populate the tasks property. Note that we’ve left out the comments in this code.

- (void)viewDidLoad

{

[super viewDidLoad];

self.tasks = [NSArray arrayWithObjects: @"Walk the dog", @"URGENT:Buy milk", @"Clean hidden lair",

@"Invent miniature dolphins", @"Find new henchmen",

@"Get revenge on do-gooder heroes", @"URGENT: Fold laundry",

@"Hold entire world hostage", @"Manicure",

nil];

}

And, of course, we need to be a good citizen and clear that out when our view is no longer going to be shown:

- (void)viewDidUnload

{

[super viewDidUnload];

//Release any retained subviews of the main view.

//e.g. self.myOutlet = nil;

self.tasks = nil;

}

Now, we get to the meat of the controller, and implement the methods that give the table view some content. Start with the simple methods that tell the table view how many sections and rows there are:

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362 CHAPTER 10: Storyboards

- (NSInteger)numberOfSectionsInTableView:(UITableView *)tableView

{

#warning Potentially incomplete method implementation. // Return the number of sections.

return 0; return 1;

}

- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section

{

#warning Incomplete method implementation.

// Return the number of rows in the section. return 0;

return [tasks count];

}

Next, replace the content of the method that populates each cell:

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath

{

static NSString *CellIdentifier = @"Cell";

UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier: CellIdentifier];

if (cell == nil) {

cell = [[UITableViewCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:CellIdentifier];

}

NSString *identifier = nil;

NSString *task = [self.tasks objectAtIndex:indexPath.row]; NSRange urgentRange = [task rangeOfString:@"URGENT"];

if (urgentRange.location == NSNotFound) { identifier = @"plainCell";

} else {

identifier = @"attentionCell";

}

UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:identifier];

// Configure the cell...

UILabel *cellLabel = (UILabel *)[cell viewWithTag:1]; cellLabel.text = task;

return cell;

}

We start off here by grabbing a task from our array, and checking to see whether it contains the string "URGENT". This is not an especially advanced algorithm for finding urgent to-do list items, but it will do for now. We use the presence or absence of the test word to decide which cell we want to load, and pick our cell identifier accordingly.

Back in Chapter 8, we showed you how to tell a table view that it can find a cell for a given identifier inside a nib file with a particular name. Putting dynamic cell prototypes inside a table view in a storyboard works similarly, with the difference that you don’t

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