flutter overlay

按钮触发产生弹框，同时底色变按，

                                        //showAlertDialog(context);

                                        //showMyDialog(context);

                                        //                               show(
                                        //                                   context: context, message: "发现新设备",message1: "目前支持LE1、部分润铂、云锦/云酷、空调"
                                        // "伴侣、墙壁插座、GDC网关，支持机型持续更新，请以实际情况为准");

                                        if (_overlayEntry != null) {
                                          _overlayEntry.remove();
                                          _overlayEntry = null;
                                          return;
                                        }
                                        _overlayEntry = OverlayEntry(
                                            builder:
                                                (context) => Positioned.fill(
                                                      top: 0,
                                                      child: Material(
                                                        color:
                                                            Colors.black54,  //设置背景暗色
                                                        child: Column(
                                                          children: [
                                                            Expanded(child:
                                                                GestureDetector(
                                                                    onTap: () {
                                                              _overlayEntry
                                                                  .remove();
                                                              _overlayEntry =
                                                                  null;
                                                            })),
                                                            Container(
                                                              child:
                                                                  new Container(
                                                                width:
                                                                    Adapt.pixel(
                                                                        674),
                                                                alignment:
                                                                    Alignment
                                                                        .center,
                                                                child:
                                                                    new Center(
                                                                  child:
                                                                      new Card(
                                                                    elevation:
                                                                        1, //设置阴影
                                                                    // shape: const RoundedRectangleBorder(
                                                                    //     borderRadius:
                                                                    //         BorderRadius.all(Radius.circular(14.0))), //设置圆角
                                                                    child:
                                                                        new Column(
                                                                      // card只能有一个widget，但这个widget内容可以包含其他的widget
                                                                      children: [
                                                                        Stack(
                                                                            overflow:
                                                                                Overflow.visible,
                                                                            children: [
                                                                              Container(
                                                                                height: Adapt.pixel(60),
                                                                                child: new ListTile(
                                                                                  title: new Text("发现新设备",
                                                                                      textAlign: TextAlign.center,
                                                                                      style: new TextStyle(
                                                                                        fontSize: 16,
                                                                                        fontWeight: FontWeight.w500,
                                                                                      )),
                                                                                ),
                                                                              ),
                                                                              Positioned(
                                                                                  top: Adapt.pixel(1),
                                                                                  right: Adapt.pixel(10),
                                                                                  child: IconButton(
                                                                                    icon: Image.asset('assets/image/icon/x.png', fit: BoxFit.cover, width: Adapt.pixel(42)),
                                                                                    onPressed: () {
                                                                                      if (_overlayEntry != null) {
                                                                                        _overlayEntry.remove();
                                                                                        _overlayEntry = null;
                                                                                        return;
                                                                                      }
                                                                                    },
                                                                                  ))
                                                                            ]),
                                                                        new ListTile(
                                                                          contentPadding:
                                                                              EdgeInsets.all(Adapt.pixel(42)),
                                                                          title: new Text(
                                                                              "目前支持LE1、部分润铂、云锦/云酷、空调"
                                                                              "伴侣、墙壁插座、GDC网关，支持机型持续更新，请以实际情况为准",
                                                                              textAlign: TextAlign.justify,
                                                                              style: new TextStyle(
                                                                                fontSize: 15,
                                                                              )),
                                                                        ),
                                                                      ],
                                                                    ),
                                                                  ),
                                                                ),
                                                              ),
                                                            ),
                                                            Expanded(child:
                                                                GestureDetector(
                                                                    onTap: () {
                                                              _overlayEntry
                                                                  .remove();
                                                              _overlayEntry =
                                                                  null;
                                                            })),
                                                          ],
                                                        ),
                                                      ),
                                                    ));
                                        Overlay.of(context)
                                            .insert(_overlayEntry);
                                      },