1

考虑以下语句：

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

取而代之的是，这里有一个帖子，用于Expression Trees像这样进行花哨的调用：

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

我在这里看到了扩展方法，下面给出。

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，并抱怨 `Cannot convert sourceType ParameterExpression to DayOfWeek。

有什么想法我在这里想念的吗？

4

2 回答 2

3

您需要传递一个有效的 lambda .. 您传递的是一个实际的DayOfWeek：

recorder.WithActivities(lambda_variable_here => "LawnMoving");
于 2013-10-21T08:29:56.010 回答
1

你需要传递参数，但是你尝试创建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类似的方法

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

如果需要从 to 传递转换方法DayOfWeek，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]);
于 2013-10-21T08:28:42.423 回答