class Metrics {
    width: Number
    left: Number
    function expand(self: Metrics, event: Event): Unit {
        self.width = 260
        self.left = 68
    }
}
class MeasuredRect: RectBlock {
    function measure(self: MeasuredRect, mount: Mount, constraints: Constraints): MeasureResult {
        parent = mount.parent()
        return MeasureResult(parent.block.metrics.width, 60)
    }
}
class OffsetColumn: Column {
    metrics: Metrics
    function arrange(self: OffsetColumn, mount: Mount, geometry: Bounds): Arrangement {
        positions = Column.arrange(self, mount, geometry)
        positions.children.at(0).x = self.metrics.left
        return positions
    }
}
metrics = Metrics(200, 44)
rect = MeasuredRect(80, 20, 0, "#526AC7")
button = Button("更新布局")
root = OffsetColumn(24, 16, rect, TextBlock("尺寸来自源码 measure，位置来自源码 arrange"), button, metrics)
connection = button.on("click", metrics.expand)
page = Page()
page.render(root)