Flutter：Function 以 function 作为参数； 设置默认 function

Question

I want to create a helper to handle my dialogs. For this I created a static method to call: I have a class DialogInstance to provide my values, that should hold style and other dialog information.

class DialogInstance {
  final BuildContext context;
  final String title;
  final String message;
  final void Function() onCancel;
  final void Function() onConfirm;
  final String confirmText;
  final String cancelText;
  final Color confirmColor;
  final Color cancelColor;

  DialogInstance.confirm(
      {@required this.context,
      @required this.title,
      @required this.message,
      @required this.onConfirm,
      Function() onCancel, // should be default set
      String confirmText,
      String cancelText,
      Color confirmColor,
      this.cancelColor})
      : this.onCancel = onCancel ?? _popContext(context), // setting default (doesn't work)
        this.confirmText = confirmText ?? 'Ok',
        this.cancelText = cancelText ?? 'Abbruch',
        this.confirmColor = confirmColor ?? Colors.red;

  static _popContext(BuildContext context) {
    Navigator.pop(context);
  }
}

I call this via:

DialogHelper.showDialog(dialogInstance: myDialog)

If I do it like this, the method _popContext gets called at initialisation and not onPressed in the dialog. How can I set this function as default and the dialog doesn't get closed at initialisation?

Answer 1

Necessary to create a new function and call pop context () => _popContext(context) . But it's impossible to create final function in constructor, use factory constructor.

class DialogInstance {
  final BuildContext context;
  final String title;
  final String message;
  final void Function() onCancel;
  final void Function() onConfirm;
  final String confirmText;
  final String cancelText;
  final Color confirmColor;
  final Color cancelColor;

  DialogInstance._(
      {this.context,
      this.title,
      this.message,
      this.onCancel,
      this.onConfirm,
      this.confirmText,
      this.cancelText,
      this.confirmColor,
      this.cancelColor});

  factory DialogInstance.confirm(
      {@required BuildContext context,
      @required String title,
      @required String message,
      @required void Function() onConfirm,
      Function() onCancel, // should be default set
      String confirmText,
      String cancelText,
      Color confirmColor,
      Color cancelColor}) {
    return DialogInstance._(
      context: context,
      title: title,
      message: message,
      onConfirm: onConfirm,
      onCancel: onCancel ?? () => _popContext(context),
      confirmText: confirmText ?? 'Ok',
      cancelText: cancelText ?? 'Abbruch',
      confirmColor: confirmColor ?? Colors.red,
    );
  }

  static _popContext(BuildContext context) {
    Navigator.pop(context);
  }
}