Flutter 89: 图解基本 Overlay 悬浮新手引导

      随着业务的扩展和延伸,需要的功能也是多种多样,而同一种效果可以有多种实现方案;小菜今天学习一下通过 Overlay 实现基本的悬浮引导效果;

      Overlay 以浮层的方式管理单独的 item 存储在栈中(后进先出);Overlay 其源码也是采用的 Stack 浮层,将 OverEntry 逐个加入到 Overlay 中进行展示,OverEntry 可以使用 PositionedAnimatedPositionedOverlay 中定义自身的位置;

      当创建 MaterialApp 时,它会自动创建一个 Navigator,之后创建一个 Overlay,然后利用这个 Navigator 来管理路由中的界面;

源码分析

const Overlay({
    Key key,
    this.initialEntries = const [],
})

class OverlayEntry 
  OverlayEntry({
    @required this.builder,
    bool opaque = false,
    bool maintainState = false,
  })
}

      分析源码可知,Overlay 主要是由 OverlayEntry 浮层元素组成的,并以栈的方式存储;opaque 为当前浮层元素是否遮盖整个 Overlay 浮层;maintainState 一般与 opaque 共同使用,是否将不透明的浮层元素添加到 Widget Tree 中;

案例尝试

      Overlay 作为浮层的应用效果很广泛,网上很多老师都通过 Overlay 实现自定义 Toast / Dialog / PopupMenu / List item 等,但小菜尝试通过 Overlay 实现升级过程中的新手引导;


      Overlay 主要是通过 insert / insertAll 方式加入 OverEntry 浮层元素,通过 remove 移除浮层元素;

insert One OverEnrty

      如果仅需展示一个 OverEntry 浮层元素,可以通过 insert 加入到 Overlay 中,也可以通过 insertAll 加入仅有一个 OverEntry 的数组;最终通过 remove 关闭浮层元素,注意数组中的元素要全部 remove

// insert
overlayEntry = OverlayEntry(builder: (context) {
  return Stack(children: [Positioned(
        top: (height - 200) * 0.5, left: (width - 200) * 0.5,
        child: GestureDetector(
            onTap: () => overlayEntry.remove(),
            child: _itemContainer(Colors.blue.withOpacity(0.6))))
  ]);
});
Overlay.of(context).insert(overlayEntry);
// insertAll
overlayEntry = OverlayEntry(builder: (context) {
  return Stack(children: [Positioned(
        top: (height - 200) * 0.5, left: (width - 200) * 0.5,
        child: GestureDetector(
            onTap: () { overlayEntry.remove(); overlayEntryList.clear(); },
            child: _itemContainer(Colors.brown.withOpacity(0.6))))
  ]);
});
overlayEntryList.add(overlayEntry);
Overlay.of(context).insertAll(overlayEntryList);

insert Three OverEntrys

      如果需要展示多个 OverEntry 浮层元素时,只能用 insertAll 添加到 Overlay 中,其中默认是以栈方式加入的;其中 insertAll 会一次性的把所有 OverEntry 均加入到 Overlay 中;

overlayEntryList.add(OverlayEntry(builder: (context) {
  return Stack(children: [
    Positioned(top: (height - 200) * 0.5 - 50, left: (width - 200) * 0.5 - 50,
        child: GestureDetector(
            onTap: () {
              --overIndex;
              overlayEntryList[overIndex].remove();
              overlayEntryList.removeLast();
            },
            child: _itemContainer(Colors.red.withOpacity(0.6))))
  ]);
}));
overlayEntryList.add(OverlayEntry(builder: (context) {
  return Stack(children: [
    Positioned(top: (height - 200) * 0.5, left: (width - 200) * 0.5,
        child: GestureDetector(
            onTap: () {
              --overIndex;
              overlayEntryList[overIndex].remove();
              overlayEntryList.removeLast();
            },
            child: _itemContainer(Colors.orange.withOpacity(0.6))))
  ]);
}));
overlayEntryList.add(OverlayEntry(builder: (context) {
  return Stack(children: [
    Positioned(top: (height - 200) * 0.5 + 50, left: (width - 200) * 0.5 + 50,
        child: GestureDetector(
            onTap: () {
              --overIndex;
              overlayEntryList[overIndex].remove();
              overlayEntryList.removeLast();
            },
            child: _itemContainer(Colors.blue.withOpacity(0.6))))
  ]);
}));
overIndex = overlayEntryList.length;
Overlay.of(context).insertAll(overlayEntryList);


      若需要逐次展示多个 OverlayEntry 可以在点击事件中单独加入新的 OverlayEntry

overlayEntry = OverlayEntry(builder: (context) {
  return Stack(children: [
    Positioned(top: (height - 200) * 0.5 - 50, left: (width - 200) * 0.5 - 50,
        child: GestureDetector(
            onTap: () {
              overlayEntry.remove();
              Overlay.of(this.context).insert(overlayEntry2);
            },
            child: _itemContainer(Colors.red.withOpacity(0.6))))
  ]);
});
overlayEntry2 = OverlayEntry(builder: (context) {
  return Stack(children: [
    Positioned(top: (height - 200) * 0.5, left: (width - 200) * 0.5,
        child: GestureDetector(
            onTap: () {
              overlayEntry2.remove();
              Overlay.of(this.context).insert(overlayEntry3);
            },
            child: _itemContainer(Colors.orange.withOpacity(0.6))))
  ]);
});
overlayEntry3 = OverlayEntry(builder: (context) {
  return Stack(children: [
    Positioned(top: (height - 200) * 0.5 + 50, left: (width - 200) * 0.5 + 50,
        child: GestureDetector(onTap: () => overlayEntry3.remove(), child: _itemContainer(Colors.blue.withOpacity(0.6))))
  ]);
});
Overlay.of(context).insert(overlayEntry);

注意事项

1. Overlay 为全局覆盖,并非当前 Page,需要重新定义返回按键等;若没有 remove 则返回上一个页面依然展示浮层元素;若 remove 其他未加入浮层的元素会返回失败;
return WillPopScope(
    onWillPop: () async {
      if (overListIndex == 6) {
        for (int i = overlayEntryList.length; i > 0; i--) {
          overlayEntryList[i - 1].remove();
        }
        overlayEntryList.clear();
        overIndex = 0;
      } else if (overListIndex == 7) {
        overlayEntry.remove();
      } else if (overListIndex == 8) {
        overlayEntry2.remove();
      } else if (overListIndex == 9) {
        overlayEntry3.remove();
      }
      if (overIndex == 4) {
        overlayEntry.remove();
        overlayEntry0.remove();
      } else if (overIndex == 3) {
        overlayEntry2.remove();
        overlayEntry0.remove();
      } else if (overIndex == 2) {
        overlayEntry3.remove();
        overlayEntry0.remove();
      } else if (overIndex == 5) {
        overlayEntry.remove();
      }
      overIndex = 0;
      return true;
    },
    child: Container(...)
);
2. 使用 insertAll 添加浮层元素时,不要同时加入多次同一个 OverlayEntry;
overlayEntry = OverlayEntry(builder: (context) {
  return Stack(children: [
    Positioned(top: (height - 200) * 0.5 - 50, left: (width - 200) * 0.5 - 50,
        child: GestureDetector(
            onTap: () => overlayEntry.remove(),
            child: _itemContainer(Colors.red.withOpacity(0.6))))
  ]);
});
// 错误写法,加入多次同一个 OverlayEntry
overlayEntryList.add(overlayEntry);
overlayEntryList.add(overlayEntry);
overlayEntryList.add(overlayEntry);

Overlay.of(this.context).insertAll(overlayEntryList);
3. opaque = true 时会完全覆盖之前的浮层元素,为不透明的,且不可透过当前浮层点击下一个浮层元素;maintainState 为在上层元素 opaque = true,即不透明的完全覆盖下层元素时,被覆盖的这个元素设置的 maintainState 是否提前构建;
overlayEntryList.add(OverlayEntry(builder: (context) {
  return Stack(children: [
    Positioned( top: (height - 200) * 0.5 - 50, left: (width - 200) * 0.5 - 50,
        child: GestureDetector(
            onTap: () { --overIndex; overlayEntryList[overIndex].remove(); },
            child: _itemContainer(Colors.red.withOpacity(0.6))))
  ]);
}));
overlayEntryList.add(OverlayEntry(
    opaque: true, maintainState: true,
    builder: (context) {
      return Material(
          color: Colors.amber.withOpacity(0.4),
          child: Stack(children: [
            Positioned( top: (height - 200) * 0.5, left: (width - 200) * 0.5,
                child: GestureDetector(
                    onTap: () { --overIndex; overlayEntryList[overIndex].remove(); },
                    child: _itemContainer(Colors.orange.withOpacity(0.6))))
          ]));
    }));
overlayEntryList.add(OverlayEntry(
    opaque: true, maintainState: false,
    builder: (context) {
      return Material(
          color: Colors.lightBlueAccent.withOpacity(0.4),
          child: Stack(children: [
            Positioned( top: (height - 200) * 0.5 + 50, left: (width - 200) * 0.5 + 50,
                child: GestureDetector(
                    onTap: () { --overIndex; overlayEntryList[overIndex].remove(); },
                    child: _itemContainer(Colors.blue.withOpacity(0.6))))
          ]));
    }));
overIndex = overlayEntryList.length;
Overlay.of(context).insertAll(overlayEntryList);

      Overlay 案例源码


      小菜对 Overlay 的尝试还比较基础,使用场景也比较小,如有错误,请多多指导!

阿策小和尚

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