Using C# to Develop for iPhone, iPod Touch and iPad

Brian Long Consultancy & Training Services Ltd.
February 2012

Accompanying source files available through this download link

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Navigation Controllers

Letís start another iPhone Master-Detail Application project. This time we'll focus more on the navigation support than the table support; the table view will simply act as a menu for some other pages. The menu will contain three items and, just to show how menu items can be grouped, weíll have some sections in the list/menu. In this case each item will be in its own section, so three sections, but it is down to your application's requirements how you apportion list items within the sections.

Make the NumberOfSections() method return 3 and RowsInSection() return 1 and then add in a TitleForHeader() method as above (entering override and choose from the list). This should be implemented thus:

public override string TitleForHeader(UITableView tableView, int section)
    switch (section)
        case 0:
            return "UIKit Example";
        case 1:
            return "CoreLocation & MapKit example";
            return "Device information example";                    

The different sections of the menu offer different choices that will exemplify different parts of the CocoaTouch library. To populate the table cells (or menu items) we need to add code to GetCell() as before. This time, though, we know we will only have a small number of cells in the list and so the reusable cell facility described earlier is not required:

public override UITableViewCell GetCell(UITableView tableView, MonoTouch.Foundation.NSIndexPath indexPath)
    var cell = new UITableViewCell(UITableViewCellStyle.Default, "");
    if ((indexPath.Section == 0) && (indexPath.Row == 0))
        cell.TextLabel.Text = "Web browser";
    if ((indexPath.Section == 1) && (indexPath.Row == 0))
        cell.TextLabel.Text = "GPS information";
    if ((indexPath.Section == 2) && (indexPath.Row == 0))
        cell.TextLabel.Text = "Device information";    
    return cell;

To give us somewhere to implement these examples we require 3 secondary pages. We already have the default secondary page in the template project, DetailViewController. However we'll ignore that one - in fact you can delete it. Right-click on DetailViewController.cs and choose Remove, then press the Delete button. Do the same with DetailViewController.xib.

You can add a new file to the solutionís active project either using File, New, File from the main menu (or CommandN) or by right-clicking your project in the Solution window and choose Add, New File... Either way, click on MonoTouch in the dialog that pops up and choose iPhone View Controller. The first one should be called BrowserViewController, then do the same and add GPSViewController and finally add a last page called InfoViewController.

Each of these new files contains a UIViewController descendant named as you specified the file should be named. When you choose an item from the table view weíll launch one of these new views so before leaving RootViewController.cs we should fill in the RowSelected() method as follows:

public override void RowSelected(UITableView tableView, MonoTouch.Foundation.NSIndexPath indexPath)
    if ((indexPath.Section == 0) && (indexPath.Row == 0))
        controller.NavigationController.PushViewController(new BrowserViewController(), true);
    if ((indexPath.Section == 1) && (indexPath.Row == 0))
        controller.NavigationController.PushViewController(new GPSViewController(), true);
    if ((indexPath.Section == 2) && (indexPath.Row == 0))
        controller.NavigationController.PushViewController(new InfoViewController(), true);

As you can see, the navigation controller can have a new view controller pushed onto its stack of view controllers. This new view controllerís view is displayed and the navigation bar will contain a button that takes you back to the previous page making return navigation straightforward.

To edit the Navigation Barís text, just assign a value to the RootViewController's Title property in its ViewDidLoad() method., e.g:

public override void ViewDidLoad ()
    base.ViewDidLoad ();
    // Perform any additional setup after loading the view, typically from a nib.
    TableView.Source = new DataSource (this);
    Title = "Brian's Stuff";

Finally, you can open up RootViewController.xib and set the Table View's Style to Grouped to enhance its appearance.

An application running in the Simulator

Note: back in the example program that used SQLite we put setup and teardown code in ViewDidLoad() and ViewDidUnload() respectively. This was fine as there was just the one view that was loaded into memory as the application started, and unloaded whenever the view is removed from memory, such as when the application exits or when memory gets low. In this application there is a menu view and then three secondary views, each of which may require setup and teardown code. Certainly when each view is first opened the ViewDidLoad() code will execute but when you navigate back to the menu ViewDidUnload() will not execute. Similarly when you go back to the same secondary view ViewDidLoad() will not execute again as it will still be loaded in memory.

It is important to decide whether the teardown code is important to execute as soon as the view is no longer visible (for performance reasons, for example) or whether it is okay to leave it until the view is eventually removed from memory. This will dictate whether you should continue to use the ViewDidLoad()/ViewDidUnload() methods or maybe switch to the ViewDidAppear()/ViewDidDisappear() methods.

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