creating-mewui-controls

name	creating-mewui-controls
description	Creates custom MewUI controls with proper measure, arrange, render, and input handling. Use when building new interactive controls, extending existing controls, or implementing custom rendering.

Control Base Classes

Base	Use Case
Control	Interactive elements (buttons, inputs)
ContentControl	Single-child containers
Panel	Multi-child layouts

---

Basic Control Structure

public class MyButton : Control
{
    private bool _isPressed;

    // Property with invalidation
    public string Text
    {
        get;
        set
        {
            if (field != value)
            {
                field = value;
                InvalidateMeasure();
            }
        }
    } = "";

    // Enable focus by overriding (not setting property)
    public override bool Focusable => true;

    // Measure: calculate desired size
    protected override Size MeasureContent(Size availableSize)
    {
        var factory = GetGraphicsFactory();
        using var ctx = factory.CreateMeasurementContext(GetDpi());
        var textSize = ctx.MeasureText(Text, GetFont());
        return new Size(textSize.Width + Padding.Horizontal, textSize.Height + Padding.Vertical);
    }

    // Render: draw the control
    protected override void OnRender(IGraphicsContext context)
    {
        var bounds = new Rect(0, 0, Bounds.Width, Bounds.Height);

        var bgColor = _isPressed ? Theme.Palette.ButtonPressedBackground
            : IsMouseOver ? Theme.Palette.ButtonHoverBackground
            : Theme.Palette.ButtonFace;

        context.FillRoundedRectangle(bounds, 4, 4, bgColor);
        context.DrawRoundedRectangle(bounds, 4, 4, Theme.Palette.BorderColor, 1);
        context.DrawText(Text, bounds, GetFont(), Foreground,
            TextAlignment.Center, TextAlignment.Center, TextWrapping.NoWrap);
    }
}

---

Input Handling

// Mouse - note: MouseEventArgs, not MouseButtonEventArgs
protected override void OnMouseDown(MouseEventArgs e)
{
    if (e.LeftButton)
    {
        _isPressed = true;
        // Capture via Window
        var root = FindVisualRoot();
        if (root is Window window)
            window.CaptureMouse(this);
        InvalidateVisual();
        e.Handled = true;
    }
}

protected override void OnMouseUp(MouseEventArgs e)
{
    if (_isPressed)
    {
        _isPressed = false;
        var root = FindVisualRoot();
        if (root is Window window)
            window.ReleaseMouseCapture();
        if (IsMouseOver) Click?.Invoke(this, EventArgs.Empty);
        InvalidateVisual();
    }
}

// Keyboard
protected override void OnKeyDown(KeyEventArgs e)
{
    if (e.Key == Key.Space || e.Key == Key.Enter)
    {
        Click?.Invoke(this, EventArgs.Empty);
        e.Handled = true;
    }
}

---

Adding Binding Support

private ValueBinding<string>? _textBinding;

public void SetTextBinding(Func<string> get, Action<string>? set = null,
    Action<Action>? subscribe = null, Action<Action>? unsubscribe = null)
{
    _textBinding?.Dispose();
    _textBinding = new ValueBinding<string>(get, set, subscribe, unsubscribe, () => Text = get());
    // RegisterBinding is internal - use within MewUI assembly
    Text = get();
}

---

Fluent Extensions

public static class MyButtonExtensions
{
    public static MyButton Text(this MyButton btn, string text) { btn.Text = text; return btn; }
    public static MyButton OnClick(this MyButton btn, Action handler) { btn.Click += (s,e) => handler(); return btn; }
    public static MyButton BindText(this MyButton btn, ObservableValue<string> src)
    {
        btn.SetTextBinding(() => src.Value, v => src.Value = v,
            h => src.Changed += h, h => src.Changed -= h);
        return btn;
    }
}

---

Input details: See input-handling.md ContentControl pattern: See content-control.md