调用在C＃中的参数中使用表达式和委托的扩展方法

Question

请考虑以下声明：

recorder.AddActivity(new Activity { ActivityName = "DeepSeaDiving", DayOfWeek = DayOfWeek.Monday });

取而代之的是，有一个帖子在这里 ，使用Expression Trees的呼看中这样的：

WeeklyActivityRecorder weeklyActivities = new WeeklyActivityRecorder () .WithActivities( Monday => "Lawn Moving",Tuesday => "Cooking");

我在这里看到了这个扩展方法，下面给出了这个方法。

public static WeeklyActivityRecorder WithActivities(this WeeklyActivityRecorder recorder, params Expression<Func<DayOfWeek, string>>[] activityList) 
    {
    foreach (var activity in activityList)
                {
                    LambdaExpression expression = activity;
                    ConstantExpression enteredActivity = expression.Body as ConstantExpression;
                    DayOfWeek day = expression.Parameters[0];
                    recorder.AddActivity(new Activity{DayOfWeek = day, ActivityName = activity});
                }

                return recorder;
    }

但是，当我编译它时，编译器对扩展方法不满意并且抱怨“无法将sourceType ParameterExpression转换为DayOfWeek” 。

我在这里缺少什么想法？

Answer 1

你需要传递一个有效的lambda ..你在实际的DayOfWeek传递：

recorder.WithActivities(lambda_variable_here => "LawnMoving");

Answer 2

您需要传递参数，但是您尝试创建lambda，其中参数名称是静态属性，大致相当于：

public string SomeMethodName(DayOfWeek.Monday) //incorrect method declaration
{

}

你需要调用WithActivities方法

recorder.WithActivities(dayOfWeek => "LawnMoving"); //dayOfWeek is a parameter name

如果需要将转换方法从DayOfWeek传递给String ，可以使用Dictionary，如下所示：

var recorder = new WeeklyActivityRecorder();

var daysTranslation = new Dictionary<DayOfWeek, string>()
{
    {DayOfWeek.Monday, "LawnMoving"}
    //other pairs
};

recorder.WithActivities(dayOfWeek => daysTranslation[dayOfWeek]);