Flutter Widget 截图

 1、定义一个GlobalKey类型的repaintKey（一对一）

GlobalKey _repaintKey = GlobalKey(); 

2、截图需用到RepaintBoundary组件，将此组件套在想要截图的组件的外层即可，同时用以上定义的repaintKey对其进行标识

RepaintBoundary(
    key: _repaintKey,
    child: <Widget>, //需要显示的Widget
),                

3、触发截图的方法，通过repaintKey拿到以上标识过需要截图的地方，进行截图

 void _saveImage() async {
    try {
      RenderRepaintBoundary boundary =
          _repaintKey.currentContext.findRenderObject();
      var image = await boundary.toImage(
          pixelRatio: MediaQuery.of(context).devicePixelRatio);
      ByteData byteData = await image.toByteData(format: ImageByteFormat.png);
      Uint8List pageBytes = byteData.buffer.asUint8List(); //图片data

      //使用image_pickers保存图片
      ImagePickers.saveByteDataImageToGallery(pageBytes).then((value) {
        //保存成功
      }).catchError((error) {
        //保存失败 
      });
    } catch (e) {
        //保存失败
    } 
  }