creating-mewui-controls

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

```csharp
// 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