Question

我有三个班，叫做学校，老师和学生。现在让我们说我有一个名为GetAcademicDetailsOfCity（）的方法，它将产生学校，教师和学生中任何类型的对象，或者可以是由三个中的任何一个派生的类。

在运行时，我想查看以下内容：

var instance = GetAcademicDetailsOfCity();
if (instance is School)
{
     //What i actually want is something like  
      var result = new School();   
      result.property1 = (School)instance.property1  
      result.property2 = (School)instance.property2  
      result.property3 = (School)instance.property3  
}

if (instance is Teacher)
{
      var result = new Teacher();  
      result.property1 = (Teacher)instance.property1  
      result.property2 = (Teacher)instance.property2  
      result.property3 = (Teacher)instance.property3  
}

if (instance is Student)
{
      var result = new Student();
      result.property1 = (Student)instance.property1  
      result.property2 = (Student)instance.property2  
      result.property3 = (Student)instance.property3 
}

如何一次检查上述条件

if (instance is School || instance is Teacher || instance is Student)
{
      //What should be the casting of instance below ??
      var result = (????)instance;
}
return result;

通过这个结果实例，我将创建一个特定学校城市学生的报告。如果需要更多详细信息，请告诉我。我很乐意尽可能多地提供详细信息:)。

Answer 1

如果GetAcademicDetailsOfCity()返回公共基本类型（即不只是Object），我们称之为MyBaseType，您可以使用else if这样来提高效率（因为它只执行一个if块，而不是像你在问题中那样执行所有三个块）：

if (instance is School)
{
    var result = (School) instance;
    // Do stuff specific to an instance of School
}
else if (instance is Teacher)
{
    var result = (Teacher) instance;
    // Do stuff specific to an instance of Teacher
}
else if (instance is Student)
{
    var result = (Student) instance;
    // Do stuff specific to an instance of Student
}

Answer 2

理想情况下，您希望这3个类中的每一个都实现一个公共接口，或者从提供GetAcademicDetailsOf函数的基类继承。这样你只需要担心最少的演员。

AcademicDetails results = instance.GetAcademicDetails();

Answer 3

用作运营商：https://msdn.microsoft.com/en-us/library/cscsdfbt.aspx

最高效的解决方案是＆＃34; as＆＃34;运营商。使用c＃进行转换比其他指令使用更多的资源。因此，你投的越少，你就越快。

var instance = GetAcademicDetailsOfCity();
var school = instance as School;
if (school != null)
{
     // do school  specific tasks
}

var teacher = instance as Teacher;
if (teacher != null)
{
     // do teacher  specific tasks
}

var student = instance as Student;
if (student != null)
{
     // do student specific tasks
}

如何检查各种“是”条件并相应地进行类型转换？

3 个答案: