November, 2009

UIAlertView / UITextField / iphone / monotouch — 2 Comments
28
Nov 09

Monotouch: UIAlertView + UITextField = Crazy Delicious

If you have ever tried to buy or install anything from the App Store or iTunes on your iPhone, then you certainly have been prompted for your password by a screen that looks like this:

itunes_pw_iphone

The control used by Apple to prompt you for your password isn’t available out-of-the-box in Cocoa Touch, but fortunately it is pretty easy to roll your own.  I’ve put together a sample project that shows a couple different techniques that are available for creating and customizing the control, and I’ll go over a few of them here.

The stock UIAlertView control consists of a title label, message label, and typically one or more buttons.  It is important to note that in Monotouch, a default button setup isn’t configured, and buttons have to be added explicitly.  If a UIAlertView is configured without any buttons, then dismissing the control will have to be done programmatically because the user will have no way to dismiss the control.  In both of my examples I’ve configured the control to have two buttons (Cancel and Ok), but I could have gotten by with just one.  If only one button is used, it is important to also note that the button is considered the Cancel button by the control, and the CancelButtonIndex property will refer to that button.

Basic_UIAlertView

The easiest way to go about composing a UIAlertView with a UITextField is to create an instance of a UITextField and add it as a sub-view.  Since you’re adding a layer on top of UIAlertView’s view, the key will be fitting this new control into the UI.  There are two ways of going about this.  The first and maybe most obvious way to solve this problem is to make some room between the message label and buttons for the text field ala the iTunes password prompt.  Since the UIAlertView control has already been laid out, moving those controls around within the frame is not as straight forward a task as it may seem.  Before we tackle that we will explore a simpler method that overlays the text field directly on top of the message label.  You sacrifice being able to display an additional message to the user, but the end result looks professional and is very easy to implement.  This will also be the basis for getting the control to have the same look and feel as the iTunes password prompt, so it is important to understand this prior to attempting to move the controls around.

The key to overlaying the text field on top of the message label is setting the bounding rectangle for the UITextField.  The bounding rectangle is where the text field draws the box in which a user enters text.  For our purposes, the rectangle needs to be drawn in between the title label and the buttons.  It is important to make sure that it covers the area where the message label is drawn.  Thanks to the work of others we know that if we start drawing the text field at the x,y offset of 12,45 that the text field will hide the message label.

The code to overlay the text field is as follows:

void PromptForName(HandlerToUse handlerType)
{
    UITextField tf = new UITextField (new System.Drawing.RectangleF (12f, 45f, 260f, 25f));
    tf.BackgroundColor = UIColor.White;
    tf.UserInteractionEnabled = true;
    tf.AutocorrectionType = UITextAutocorrectionType.No;
    tf.AutocapitalizationType = UITextAutocapitalizationType.None;
    tf.ReturnKeyType = UIReturnKeyType.Done;
    tf.SecureTextEntry = false; 

    UIAlertView myAlertView = new UIAlertView
    {
        Title = "Please enter your name",
        Message = "this line is hidden"
    };

    myAlertView.AddButton("Cancel");
    myAlertView.AddButton("Ok");
    myAlertView.AddSubview(tf);
    // More Setup Goes Here
    myAlertView.Show ();
}

The method starts by instantiating a UITextField control with a bounding rectangle passed via its constructor.  The rectangle itself is constructed with four parameters via its constructor: the first two parameters set the x and y offset from the origin point of the control, and the last two parameters set the size of the drawing area.  After the initial construction of the UITextField, a few additional properties are set to customize the display. 

Among the properties set is the SecureTextEntry.  Setting this property to true will make the text field act like a password field and hide all the characters that you’ve entered.  Once the text field has been created and initialized, we move on to creating a UIAlertView.  Via object initialization, the Title and Message properties are set with some text.  Finally, two buttons are created, and the text field is added as a sub-view to the UIAlertView.  Calling the show on the UIAlertView causes the alert to pop up.  Below you can see the rendered control.

TextField_As_Subview_UIAlertView

So now that we have the basic control setup, we can tweak it so that the text field and the message label can both be displayed.

If you recall our custom UIAlertView control is currently composed of two UILabels, two UIButtons and a UITextField that we added.  The UILabels are derived from UIView and is not a subclass of UIControl; whereas, the UIButton and the UITextField are both derived from UIControls.  Since we want to position the UITextField beneath the labels, we can use this knowledge to selectively shift only the UIControls in the view down leaving the title and message labels in place.

To accomplish this task the following steps need to be performed:

1) The control height needs to be increased to make space for the text field and provide additional space to move the UIControls.  This is done by setting the frame to a larger size.  The frame will be increased by the height of the text field plus a buffer, so the control has space between it and the others.

This is what the frame looks like after being enlarged:

FrameEnlarged_CustomUIAlertView 


2) Once the frame has been enlarged, we’ll loop through the sub-views looking for UIControls and adjust only those types down by the same text field plus buffer offset

Here is what the control looks like after each UIControl is found during the iteration through the sub-views.

FirstUIControlShifted_CancelButton

SecondUIControlShifted_OkButton

FinalUIControlShifted_TextField

Here is the code that does the control adjustment:

public class TextFieldAlertView : UIAlertView
{
    private UITextField _tf;

    // ... 

    private void AdjustControlSize()
    {
        float tfExtH = _tf.Frame.Size.Height + 16.0f;

        var frame = new RectangleF(this.Frame.X,
                                    this.Frame.Y - tfExtH/2,
                                    this.Frame.Size.Width,
                                    this.Frame.Size.Height + tfExtH);

        this.Frame = frame;

        foreach(var view in this.Subviews)
        {
            if(view is UIControl)
            {
                view.Frame = new RectangleF(view.Frame.X,
                                            view.Frame.Y + tfExtH,
                                            view.Frame.Size.Width,
                                            view.Frame.Size.Height);
            }
        }
    }
}

So now that the desired look and feel of the control has been established, it is time to wire up the control.  There are a couple options for handling events generated by the control: one is more in line with how Cocoa handles events, and another that is similar to how .Net works. 

The Cocoa way to wire up delegates involves subclassing a special delegate class associated to the control and selectively overriding the methods for the actions you want to customize.  In the case of the UIAlertView control, that delegate class is a UIAlertViewDelegate.  The delegate class includes overridable methods like Clicked where you can define the actions to take when a button on the control is clicked or where you can extend behaviors by overriding methods like Preseneted which is called after the control has been displayed to the user.

The .Net way to wire up events is to provide specific delegates for specific events.  To make interacting with the Cocoa Touch controls easier, Monotouch provides public events for each one of the methods that can be overridden in the UIAlertViewDelegate class.  Having the individual public events makes wiring up controls more intuitive for the .Net developer, but it is good to know about the Cocoa-style approach especially when looking at Objective-C examples and/or ADC docs.  I have examples of wiring up the control via both methods in the example source.

The last topic I’d like to cover briefly is how I encapsulated the customization of control by subclassing UIAlertView.  The key to getting the control to look right is to override the LayoutSubviews method and build out the text field, add it to the UIAlertView and shift the controls around there.

public override void LayoutSubviews ()
{
    // layout the stock UIAlertView
    base.LayoutSubviews ();

    // build out the text field
    _tf = ComposeTextFieldControl(_secureTextEntry);

    // add the text field to the UIAlertView
    this.AddSubview(_tf);

    // shift the UIControls to fit the text field
    AdjustControlSize();
}

I’ve added some more customizations to my subclassed UIAlertView control that allows you to enable the text field security via a constructor parameter and a tweak to the control’s Transform property to shift the control up so it isn’t hidden by the keyboard.  You can see those changes and the entire working example here on github.

Enjoy.

Links to some of the resources used:

C# / UITableView / UITableViewController / cocoa touch / development / iphone / monotouch — 2 Comments
22
Nov 09

Fun with Monotouch and Multi-Level Table Views without Interface Builder

With the recent release of  Monotouch, which enabled development for the iPhone/iPod Touch platform using C# and .Net, it seemed like the perfect time to take a swing at mobile app development.  The strong appeal of being able to leverage my C# and .Net experience while scratching an itch that I have had for a few apps was more than enough to entice me to order a brand new Mac mini and start learning the Cocoa framework.

My pet app project requires some pretty basic multi-level tabular data visualization, so that was the first thing I attempted to tackle.  I started my learning endeavor by reading the view controller programming guide from Apple’s ADC and working through a few of the tutorials listed on the Monotouch site.  One of the example tutorials listed was for a basic RSS reader.  Armed with his guide, I got up and running with a basic table view allowed me to drill down one level deep and return to the root via navigation button.  This was a great introduction and the easy to follow steps combined with the screenshots certainly hit the mark; however, this was not quite the layout I was looking for.

The data that I wanted to display calls for more than just a list-view-to-detail-view relationship that the RSS reader implemented.  As a beginner trying to figure out how to wire up my custom table controllers to each other and the navigation controller all via Interface Builder resulted in a lot of thrashing and a lot of ugly code.  I eventually was able to roughly approximate the behavior I wanted, but it was pretty obvious to me there had to be a better way.

I set out to see if I could find more Monotouch examples to see if I could pick up some tips and stumbled across Craig Dunn’s blog.  Craig not only put together apps for the Monospace and PDC conferences (and graciously provided the source) but also posted a Roget’s Thesaurus app that was just what I was looking for.  It was a simple app, but it had all the elements in play that I was looking for and an incredible diagram that tied it all together.

One of the key tips and tricks I picked up from Craig’s code was how easy it was to cut out the Interface Builder from the process.  I also generally tend to avoid using the designer whenever possible in Visual Studio but here it was a key factor in my understand.  This isn’t to say that I’d never use the Interface Builder again or that it doesn’t have its uses because it does but there was too much magic going on in how Monotouch links up the XIBs to their backing C# classes.  It wasn’t until I started explicitly creating views and view controllers instead of trying to wire them up after the fact did I start to understand how things were supposed to interact.

To implement a custom UITableViewController you need to set two properties with custom classes and override a method which is invoked by the framework when the view controller is loaded.  You’ll need to set the TableDelegate and DataSource properties on the controller with your own implementations of UITableViewDelegate and  UITableViewDataSource.  The implementation of the table delegate allows you to customize how the table will respond to certain events and the data source implementation provides not only the data the table uses but also how that data is to be displayed within the table.  Typically the ViewDidLoad method is overriden to perform the view setup work needed during initialization of the view controller.  Within the method the TableDelegate and DataSource properties can be set.

Example setting the TableDelegate and DataSource via the ViewDidLoad method:

namespace MultiLevelTableView
{
    [MonoTouch.Foundation.Register("RootViewController")]
    public partial class RootViewController : UITableViewController
    {
        class DataSource : UITableViewDataSource { /* Impl Here */ }

        class TableDelegate : UITableViewDelegate { /* Impl Here */ }

        public override void ViewDidLoad ()
        {
            base.ViewDidLoad ();

            TableView.Delegate = new TableDelegate (this);
            TableView.DataSource = new DataSource (this);
        }
    }
}

Example setting the properties during UITableView construction:

namespace MultiLevelTableView
{
    [MonoTouch.Foundation.Register("RootViewController")]
    public partial class RootViewController : UITableViewController
    {
        UITableView tableView;

        class DataSource : UITableViewDataSource { /* Impl Here */ }

        class TableDelegate : UITableViewDelegate { /* Impl Here */ }

        public override void ViewDidLoad ()
        {
            base.ViewDidLoad ();

            tableView = new UITableView()
            {
                Delegate = new TableViewDelegate(this),
                DataSource = new TableViewDataSource(this),
            };

            //You can set more properties here like size and
            //location in the frame etc.

            this.View.AddSubview(tableView);
        }
    }
}

The meat of the table view controller falls in the implementations of the DataSource and TableDelegate.

A basic DataSource setup involves overriding two methods used by parent controller.  The RowsInSection method tells how many rows need to be displayed in the table and the GetCell method returns a cell view which was customized for display by setting the text and display properties.

class DataSource : UITableViewDataSource
{
    static NSString kCellIdentifier = new NSString ("MyIdentifier");
    RootViewController tvc;

    public DataSource (RootViewController tvc)
    {
        this.tvc = tvc;
    }

    public override int RowsInSection (UITableView tableView, int section)
    {
        return tvc.RootData.Count;
    }

    public override UITableViewCell GetCell (UITableView tableView, NSIndexPath indexPath)
    {
        var cell = tableView.DequeueReusableCell (kCellIdentifier);

        if (cell == null)
        {
            cell = new UITableViewCell (UITableViewCellStyle.Default, kCellIdentifier);
        }

        cell.TextLabel.Text = tvc.RootData.ElementAt(indexPath.Row);
        cell.Accessory = UITableViewCellAccessory.DetailDisclosureButton;
        return cell;
    }
}

The TableDelegate is where the behavior of the table to various events is defined.  It is here in which we load up the next view to display when a user clicks on a cell.   A basic implementation of a table view delegate involves overriding the RowSelected method with instructions on what to do with the row now that it has been selected.  If the node selected happened to be a leaf node for example we might load up the detail’s view to display the nodes properties or if the node was the parent of more child nodes we would load another list view to continue to drill down into the data.  In our case we want to drill down to the next layer of data which is managed by the SubGroupViewController.

class TableDelegate : UITableViewDelegate
{
    RootViewController tvc;
    SubGroupViewController sgvc;

    public TableDelegate (RootViewController tvc)
    {
        this.tvc = tvc;
    }

    public override void RowSelected (UITableView tableView, NSIndexPath indexPath)
    {
        // get info from selected row
        string selectedGroup = tvc.RootData.ElementAt(indexPath.Row);

        // load up new controller to display
        if(sgvc == null)
            sgvc = new SubGroupViewController(selectedGroup);

        // push the controller on the navigation stack
        tvc.NavigationController.PushViewController(sgvc, true);
    }
}

The hang up for me with using Interface Builder to try and get the multi-level table views wired together was mostly due to not being familiar with the objects I was dealing with and not understanding what properties are needed to be initialized so the framework can display them correctly.  Approaching the problem via the Interface Builder created a lot of noise that made seeing what was really needed to wire these table view controllers with the navigation controller difficult.  In this case the the pre-packaged templates and generic layouts provided by Monotouch and Interface Builder were more of a hindrance than help but that is to be expected while learning a new technology.

I’ve packaged up my implementation of a multi-level table view app and put it on github.  If anyone is looking for straight-forward, simple example of nesting table views hopefully this will help.

I also recommend checking out the following links which helped me immensely: