Utiliser des exceptions spécifiques dans un bloc CatchHow to use specific exceptions in a catch block

En général, il est conseillé en programmation d’intercepter un type d’exception spécifique au lieu d’utiliser une instruction catch de base.In general, it's good programming practice to catch a specific type of exception rather than use a basic catch statement.

Quand une exception se produit, elle remonte la pile et chaque bloc catch a la possibilité de la gérer.When an exception occurs, it is passed up the stack and each catch block is given the opportunity to handle it. L’ordre des instructions catch est important.The order of catch statements is important. Placez les blocs catch ciblés sur des exceptions spécifiques avant un bloc catch d’exceptions générales, sinon le compilateur peut générer une erreur.Put catch blocks targeted to specific exceptions before a general exception catch block or the compiler might issue an error. Le bloc catch approprié est déterminé en mettant en correspondance le type de l’exception avec le nom de l’exception spécifiée dans le bloc catch.The proper catch block is determined by matching the type of the exception to the name of the exception specified in the catch block. S’il n’existe aucun bloc catch spécifique, l’exception est interceptée par un bloc catch général, le cas échéant.If there is no specific catch block, the exception is caught by a general catch block, if one exists.

L’exemple de code suivant utilise un bloc try/catch pour intercepter une exception InvalidCastException.The following code example uses a try/catch block to catch an InvalidCastException. L’exemple crée une classe appelée Employee avec une propriété unique, le niveau de l’employé (Emlevel).The sample creates a class called Employee with a single property, employee level (Emlevel). Une méthode PromoteEmployee prend un objet et incrémente le niveau de l’employé.A method, PromoteEmployee, takes an object and increments the employee level. Une exception InvalidCastException se produit quand une instance DateTime est passée à la méthode PromoteEmployee.An InvalidCastException occurs when a DateTime instance is passed to the PromoteEmployee method.

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();
}
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.
        var 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);
        }
    }
}
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

Voir aussiSee also