Question

在我的表格顶部，我有：

public static int hoursInt;
public static int minutesInt;
public static int secondsInt;
public static int CompletedIn24;

然后再往下我有以下内容在选择新跑步者时将numericUpDown框重置为零：

private void lstRunners_SelectedIndexChanged(object sender, EventArgs e)
{

Runner selectedRunner = (Runner)lstRunners.SelectedItem;

numericUpDown1.Value = 0;
numericUpDown2.Value = 0;
numericUpDown3.Value = 0;
}

然后在Finish按钮点击事件中我有：

 hoursInt = Convert.ToInt32(numericUpDown1.Value);
 minutesInt = Convert.ToInt32(numericUpDown2.Value);
 secondsInt = Convert.ToInt32(numericUpDown3.Value);

if (lstRunners.SelectedIndex > -1 && hoursInt + minutesInt + secondsInt != 0)
        {
            // Obtain selected climber
            Runner selectedRunner = (Runner)lstRunners.SelectedItem;
            selectedRunner.Hours = hoursInt;
            selectedRunner.Minutes = minutesInt;
            selectedRunner.Seconds = secondsInt;

            var expertRunner = selectedRunner as Expert;
            if (expertRunner != null)
            {
                expertRunner.UponFinish();
            }

以下是Expert : Runner中的覆盖方法：

public override void UponFinish()
        {
            base.UponFinish();

            // The integer must increment by one if the time is 24:00:00 or less i.e. 23:59:59 would increment the integer as well
            if (Hours < 24 || (Hours == 24 && Minutes == 0 && Seconds == 0))
            {
                CompletedIn24++;
            }
        }

目前UponFinish()中的Runner方法在括号内没有任何内容，因为我不确定是否需要任何内容？

我尝试将CompletedIn24整数输出到字符串，以查看单击按钮时它是否有效，但即使选择了专家运动员且时间为24:00:00，该值也保持为零或更少。整数没有递增，我不确定导致问题的原因是什么？

任何帮助都将不胜感激。

Answer 1

只需使用as关键字，如下所示：

var runner = selectedRunner as Expert;
if(runner != null) runner.UponFinish();

如果您的类Runner已经定义了一个名为UponFinish的方法，那么您应该将此方法定义为virtual并在派生类中重写该方法，如下所示：

public class Runner {
  public virtual void UponFinish(){
     //...
  }
}
public class Expert : Runner {
  public override void UponFinish(){
    //You talked about the time, I asked for clarification on this
    //but it's still very unclear. I suppose when you mean the time is 24:00:00
    //that means the hours is 24, the minutes is 0 and the seconds is 0
    if(Hours < 24 || (Minutes == 0 && Seconds == 0)) Completedin24++;
  }
}

然后当然你不需要任何演员表，只需调用UponFinish并且正确调用被覆盖的代码（如果有的话）：

selectedRunner.UponFinish();

Answer 2

你可以检查这样的类型：

if (selectedRunner.GetType() == typeof(Expert))
{
    Expert expert = (Expert)selectedRunner;
}

Answer 3

你可以做到

if(selectedRunner is Expert)
{
    UponFinish((Expert)selectedRunner);
    //or ((Expert)selectedRunner).UponFinish(); if that was the intention
}

或者

Expert selectedExpert = selectedRunner as Expert;
if(selectedExpert != null)
    UponFinish(selectedExpert);

编辑：

如果您的UponFinish功能已经同时属于Runner和Expert（即在Expert中覆盖），则无需在调用之前投射selectedRunner它

Answer 4

有几种方法可以做到这一点，例如运算符is： Operator IS

Answer 5

您可以使用is关键字检查您的Runner是否是ExpertRunner：

if(selectedRunner is ExpertRunner)

但是，就OOP而言，你不应该这样做，你可能想要检查你的层次结构或逻辑，为什么你需要单独处理这个案例而不是被覆盖的行为（函数或属性）。

Answer 6

试试这个：

if(lstRunners.SelectedItem is Expert)
{
    Expert selectedRunner = lstRunners.SelectedItem as Expert;
    selectedRunner.UponFinish();
}

Answer 7

if (lstRunners.SelectedItem is Expert)
{
    ((Expert)lstRunners.SelectedItem).UponFinish();
}

如何在语句中引用类的对象？

7 个答案: