Dart Flutter：為類構造函數設置默認值時，可選參數的默認值必須是常量

Question

我創建了一個類JobBloc ，其中包含許多屬性，其中一個是另一個類對象JobModel ，我想為這些屬性中的每一個分配一個默認值，除了JobModel屬性外，它工作正常：

class JobBloc with JobModelFormValidator {
  final JobModel jobModel;
  final bool isValid;
  final bool showErrorMessage;
  final String name;
  final double ratePerHour;
  final bool enableForm;
  final bool showIcon;

  JobBloc({
    // The default value of an optional parameter must be constant.
    this.jobModel = JobModel(name: 'EMPTY', ratePerHour: 0.01), // <= the error stems from this line
    this.isValid = false,
    this.showErrorMessage = false,
    this.name = 'EMPTY',
    this.enableForm = true,
    this.ratePerHour = 0.01,
    this.showIcon = false,
    });
}

如何為我的jobModel屬性分配默認值？

Answer 1

您不能在類模型中初始化對象。

嘗試：

class JobBloc with JobModelFormValidator {
  final JobModel jobModel;
  final bool isValid;
  final bool showErrorMessage;
  final String name;
  final double ratePerHour;
  final bool enableForm;
  final bool showIcon;

  JobBloc({
    this.isValid = false,
    this.showErrorMessage = false,
    this.name = 'EMPTY',
    this.enableForm = true,
    this.ratePerHour = 0.01,
    this.showIcon = false,
    }) : jobModel = JobModel(name: 'EMPTY', ratePerHour: 0.01);
}

或者更新 jobModel 類

class JobModel {
  final String name;
  final double ratePerHour;

  JobModel({
    this.name = 'EMPTY',
    this.ratePerHour = 0.01,
  });
}

Answer 2

試試這個可能是？

class JobBloc with JobModelFormValidator {
  final JobModel jobModel;
  final bool isValid;
  final bool showErrorMessage;
  final String name;
  final double ratePerHour;
  final bool enableForm;
  final bool showIcon;

  JobBloc({
    this.jobModel = const JobModel(name: 'EMPTY', ratePerHour: 0.01),
    this.isValid = false,
    this.showErrorMessage = false,
    this.name = 'EMPTY',
    this.enableForm = true,
    this.ratePerHour = 0.01,
    this.showIcon = false,
    });
}