设置一个按钮调用   打开showCupertinoModalPopup

FloatingActionButton(onPressed: (){
            _showDialog(context);
          },

            child: Text('aaaaaa'),),
　　打开底部弹出框

 void _showDialog(BuildContext cxt){
    showCupertinoModalPopup<int>(context: cxt, builder:(cxt){
      var dialog =CupertinoActionSheet(
        title: Text("请选择"),
//        message: Text('上传作业!'),
        cancelButton: CupertinoActionSheetAction(onPressed: (){
          Navigator.pop(cxt,0);
        }, child: Text("取消")),
        actions: <Widget>[
          CupertinoActionSheetAction(onPressed: (){
            showImagePicker(1);
            Navigator.pop(cxt,1);

          }, child: Text('相机')),

          CupertinoActionSheetAction(onPressed: (){
            showImagePicker(2);
            Navigator.pop(cxt,2);
          }, child: Text('相册')),
        ],
      );
      return dialog;
    });
  }



　　根据选择的设备进行调用相机或者相册

showImagePicker(type) async{
　　

/// Specifies the source where the picked image should come from.
enum ImageSource {  这个是调用源码
  /// Opens up the device camera, letting the user to take a new picture.
  camera,

  /// Opens the user's photo gallery.
  gallery,
}

  var image = await ImagePicker.pickImage(source: type ==1?ImageSource.camera: ImageSource.gallery);  枚举类型 设置调用的类型camera 相机  另外一个是本地相册

  setState(() {
    _image = image;
  });

}

需要引入的包：

import 'package:image_picker/image_picker.dart';
import 'package:flutter/cupertino.dart';