add sticky header demo

doric-demo/src/StickyHeaderDemo.ts

@@ -0,0 +1,63 @@
+import { Group, Panel, vlayout, scroller, text, layoutConfig, stack, Color, View, Scroller } from "doric";
+
+const colors = [
+    "#70a1ff",
+    "#7bed9f",
+    "#ff6b81",
+    "#a4b0be",
+    "#f0932b",
+    "#eb4d4b",
+    "#6ab04c",
+    "#e056fd",
+    "#686de0",
+    "#30336b",
+].map(e => Color.parse(e))
+
+function titleBar() {
+    return text({
+        text: "This is a sticky header",
+        layoutConfig: layoutConfig().mostWidth().justHeight(),
+        height: 50,
+        backgroundColor: Color.YELLOW
+    })
+}
+
+@Entry
+export class StickyHeaderDemo extends Panel {
+    build(root: Group) {
+        let stickyHeader: View
+        let scrollerView: Scroller
+        stack(
+            [
+                scroller(
+                    vlayout(
+                        [
+                            stack([], {
+                                layoutConfig: layoutConfig().mostWidth().justHeight(),
+                                height: 80,
+                                backgroundColor: Color.GRAY,
+                            }),
+                            titleBar(),
+                            ...new Array(20).fill(0).map((_, index) => stack([], {
+                                layoutConfig: layoutConfig().mostWidth().justHeight(),
+                                height: 80,
+                                backgroundColor: colors[index % colors.length]
+                            })),
+                        ],
+                        {
+                            layoutConfig: layoutConfig().mostWidth().fitHeight(),
+                        }
+                    ),
+                    {
+                        layoutConfig: layoutConfig().most(),
+                        onScroll: (offset) => {
+                            stickyHeader.hidden = offset.y <= 80
+                        }
+                    }),
+                stickyHeader = titleBar().apply({ hidden: true }),
+            ],
+            {
+                layoutConfig: layoutConfig().most(),
+            }).in(root)
+    }
+}