Creating Custom UI Controls with MonoTouch.Dialog

Introduction

MonoTouch.Dialog is a popular open-source library for creating custom dialog boxes on iOS devices. While it provides many useful features, there are times when you need more control over the UI or want to create custom controls that aren’t directly supported by the library.

In this article, we’ll explore one such scenario: creating a checkbox selection list using MonoTouch.Dialog. This might seem like an impossible task at first glance, but with some creativity and extension of the existing library, it’s actually quite feasible.

Understanding RadioSelection

Before diving into custom checkboxes, let’s quickly revisit the RadioSelection attribute from MonoTouch.Dialog. This attribute allows users to select a single option from a list of radio buttons.

[RadioSelection]
private string selectedOption;

The key aspect of RadioSelection is that it only enables one option at a time, making it suitable for scenarios where you need a single selection. However, what if you want to allow multiple selections? This is where things get interesting.

Understanding the Challenge

At first glance, creating a checkbox selection list using MonoTouch.Dialog might seem like an impossible task. The library doesn’t provide built-in support for checkboxes, and modifying existing controls requires some knowledge of UIKit and iOS UI programming.

However, by extending the MTDialog class, we can create a custom control that mimics the behavior of checkboxes. This approach will require some additional code and understanding of the underlying mechanics, but it’s doable with some creativity and persistence.

Creating a Custom Checkbox Control

To start creating our custom checkbox control, we’ll need to extend the MTDialog class. We’ll override the draw method, which is responsible for rendering the dialog box. In this method, we’ll create a custom control that will behave like a checkbox.

using MonoTouch.Dialog;

public class CustomCheckbox : MTDialogButtonCell
{
    private bool isChecked;
    private UIColor checkedColor = UIColor.Green;
    private UIColor uncheckedColor = UIColor.Gray;

    public override void Draw (RectangleF rect)
    {
        base.Draw(rect);

        // Create a new graphics context for drawing
        var graphics = UIGraphics.GetCurrentContext();

        // Calculate the size of the checkbox
        var checkboxSize = new SizeF {Width = 16, Height = 16};

        // Draw the background rectangle
        graphics.SetFillColor(Color.White);
        graphics.FillRect(new Rect(rect.X + 2, rect.Y + 2, checkboxSize.Width - 4, checkboxSize.Height - 4));

        // Draw the checkbox itself
        if (isChecked)
        {
            graphics.SetFillColor(checkedColor);
        }
        else
        {
            graphics.SetFillColor(uncheckedColor);
        }

        var rectangle = new Rect(rect.X + 2, rect.Y + 2, checkboxSize.Width - 4, checkboxSize.Height - 4);
        graphics.FillRect(rectangle);

        // Draw the toggle button
        graphics.SetFillColor(Color.White);
        graphics.DrawRectangle(new Rect(rect.X + 2, rect.Y + 2, checkboxSize.Width - 4, checkboxSize.Height - 4), new FloatRect(0, 0, 1, 1));
    }

    public bool IsChecked => isChecked;
    public void SetChecked(bool checkedValue)
    {
        isChecked = checkedValue;
    }
}

In this code snippet, we’ve created a custom CustomCheckbox class that inherits from MTDialogButtonCell. We override the Draw method to draw a checkbox control. The checkbox is drawn using two rectangles: one for the background and another for the toggle button.

The isChecked property keeps track of whether the checkbox is checked or not, and the SetChecked method allows you to update this value.

Creating a Custom Selection List

Now that we have our custom checkbox control, let’s create a selection list that uses these checkboxes instead of radio buttons. We’ll extend the MTDialog class again to add a new property called SelectionList.

using MonoTouch.Dialog;

public class CustomSelectionDialog : MTDialog
{
    private IList<object> selections;
    public IList<object> Selections { get; set; }

    public override void LoadContent (object content)
    {
        base.LoadContent(content);

        // Create a new list of checkboxes
        var checkboxes = new List<CustomCheckbox>();

        foreach (var selection in Selections)
        {
            var checkbox = new CustomCheckbox();
            checkbox.SetChecked(selection.Equals(this));
            checkboxes.Add(checkbox);
        }

        // Add the checkboxes to the dialog box
        foreach (var checkbox in checkboxes)
        {
            AddButton(checkbox);
        }
    }
}

In this code snippet, we’ve created a custom CustomSelectionDialog class that extends MTDialog. We add a new property called Selections, which is an IList<object>. This list will contain the values to be displayed in our selection list.

In the LoadContent method, we create a new list of checkboxes and set their checked state based on the values in our Selections list. We then add these checkboxes to the dialog box using the AddButton method.

Using Our Custom Selection List

Finally, let’s see how we can use our custom selection list. We’ll create an instance of our CustomSelectionDialog class and pass it a list of values.

using MonoTouch.Dialog;

class Program
{
    static void Main (string[] args)
    {
        // Create a new list of values
        var values = new List<string> { "Option 1", "Option 2", "Option 3" };

        // Create an instance of our custom selection dialog
        var dialog = new CustomSelectionDialog();
        dialog.Selections = values;

        // Show the dialog box
        dialog.Show();

        // Wait for the user to select some options
        while (dialog.IsShowing)
        {
            // Update the UI here...
        }
    }
}

In this code snippet, we create a new list of values and pass it to our CustomSelectionDialog instance. We then show the dialog box and wait for the user to select some options.

Conclusion

Creating a checkbox selection list using MonoTouch.Dialog is certainly possible with some creativity and extension of the existing library. By creating custom controls like checkboxes, we can add more functionality to our dialog boxes.

Of course, this approach requires some additional code and understanding of UIKit and iOS UI programming. But with the right knowledge and tools, you can create custom UI controls that meet your specific needs.

Note: This article is a simplified example of how to extend MonoTouch.Dialog to create a checkbox selection list. In a real-world scenario, you would likely need to consider additional factors like data binding, event handling, and more.

Last modified on 2024-12-12