awesome-uiwidgets/AwesomeUIWidgets/Assets/Scripts/Widgets/send_button.cs

using Unity.UIWidgets.foundation;
using Unity.UIWidgets.material;
using Unity.UIWidgets.painting;
using Unity.UIWidgets.widgets;

namespace UIWidgetsSample
{
    public class SendButton : StatelessWidget
    {
        /// Callback for send button tap event
        public readonly OnPressed onPressed;

        /// Creates send button widget
        public SendButton(
            OnPressed onPressed,
            Key key = null
        ) : base(key)
        {
            this.onPressed = onPressed;
        }

        public override Widget build(BuildContext context)
        {
            Widget icon =  InheritedChatTheme.of(context).theme.sendButtonIcon != null
                ? InheritedChatTheme.of(context).theme.sendButtonIcon
                : Image.file(
                    "assets/icon-send.png",
                    color: InheritedChatTheme.of(context).theme.inputTextColor,
                    scale: 1
                );
            var tooltip = InheritedL10n.of(context).l10n?.sendButtonAccessibilityLabel;
            return new Container(
                height: 20,
                margin: EdgeInsets.only(right:16),
                width: 30,
                child: new IconButton(
                    icon: icon,
                    onPressed: () => { onPressed(); },
                    padding: EdgeInsets.zero,
                    tooltip: tooltip
                )
            );
        }
    }
}