HOW TO：使用 Catch 區塊中的特定例外狀況
當例外狀況發生時，它會在堆疊中向上傳遞，而讓各個 Catch 區塊都有機會來處理它。 Catch 陳述式的順序很重要。 請針對特定例外狀況將 Catch 區塊放在一般例外狀況 Catch 區塊之前，否則編譯器 (Compiler) 可能會發出錯誤。 適當的 Catch 區塊會藉著將 Catch 區塊中指定的例外狀況名稱與例外狀況類型作比對來決定。 如果沒有特定的 Catch 區塊，例外狀況由一般 Catch 區塊 (若有一個的話) 來攔截。
下列程式碼範例使用 Try/Catch 區塊來攔截 InvalidCastException。 範例建立稱為 Employee 的類別，它具有單一屬性「員工職等」(Emlevel)。 方法 , PromoteEmployee 會接受物件並增加員工職等。 當 DateTime 執行個體傳遞至 PromoteEmployee 方法時，就會發生 InvalidCastException。
範例
Imports System
Public Class Employee
'Create employee level property.
Public Property Emlevel As Integer
Get
Return emlevelValue
End Get
Set
emlevelValue = Value
End Set
End Property
Private emlevelValue As Integer = 0
End Class
Public Class Ex13
Public Shared Sub PromoteEmployee(emp As Object)
'Cast object to Employee.
Dim e As Employee = CType(emp, Employee)
' Increment employee level.
e.Emlevel = e.Emlevel + 1
End Sub
Public Shared Sub Main()
Try
Dim o As Object = New Employee()
Dim newyears As New DateTime(2001, 1, 1)
'Promote the new employee.
PromoteEmployee(o)
'Promote DateTime; results in InvalidCastException as newyears is not an employee instance.
PromoteEmployee(newyears)
Catch e As InvalidCastException
Console.WriteLine("Error passing data to PromoteEmployee method. " + e.Message)
End Try
End Sub
End Class
using System;
public class Employee
{
//Create employee level property.
public int Emlevel
{
get
{
return(emlevel);
}
set
{
emlevel = value;
}
}
private int emlevel = 0;
}
public class Ex13
{
public static void PromoteEmployee(Object emp)
{
//Cast object to Employee.
Employee e = (Employee) emp;
// Increment employee level.
e.Emlevel = e.Emlevel + 1;
}
public static void Main()
{
try
{
Object o = new Employee();
DateTime newyears = new DateTime(2001, 1, 1);
//Promote the new employee.
PromoteEmployee(o);
//Promote DateTime; results in InvalidCastException as newyears is not an employee instance.
PromoteEmployee(newyears);
}
catch (InvalidCastException e)
{
Console.WriteLine("Error passing data to PromoteEmployee method. " + e.Message);
}
}
}
using namespace System;
public ref class Employee
{
public:
Employee()
{
emlevel = 0;
}
//Create employee level property.
property int Emlevel
{
int get()
{
return emlevel;
}
void set(int value)
{
emlevel = value;
}
}
private:
int emlevel;
};
public ref class Ex13
{
public:
static void PromoteEmployee(Object^ emp)
{
//Cast object to Employee.
Employee^ e = (Employee^) emp;
// Increment employee level.
e->Emlevel++;
}
static void Main()
{
try
{
Object^ o = gcnew Employee();
DateTime^ newyears = gcnew DateTime(2001, 1, 1);
//Promote the new employee.
PromoteEmployee(o);
//Promote DateTime; results in InvalidCastException as newyears is not an employee instance.
PromoteEmployee(newyears);
}
catch (InvalidCastException^ e)
{
Console::WriteLine("Error passing data to PromoteEmployee method. " + e->Message);
}
}
};
int main()
{
Ex13::Main();
}
Common Language Runtime 會攔截未被 Catch 區塊攔截的例外狀況。 取決於執行階段如何被設定，不是偵錯對話方塊出現，就是程式停止執行而出現帶有例外狀況資訊的對話方塊。 如需偵錯的詳細資訊，請參閱偵錯和分析應用程式。