ConstraintCollection.CollectionChanged Event

Definition

Occurs whenever the ConstraintCollection is changed because of Constraint objects being added or removed.

public event System.ComponentModel.CollectionChangeEventHandler? CollectionChanged;
public event System.ComponentModel.CollectionChangeEventHandler CollectionChanged;

Event Type

Examples

The following example demonstrates how to use the CollectionChanged event.

private static void ConstraintCollectionChanged()
{
    // Demonstrate ConstraintCollection.CollectionChanged event.
    try
    {
        // Create Customers table.
        DataTable customersTable = new DataTable("Customers");
        customersTable.Columns.Add("id", typeof(int));
        customersTable.Columns.Add("Name", typeof(string));
        customersTable.Constraints.CollectionChanged +=
            new System.ComponentModel.CollectionChangeEventHandler(
            Collection_Changed);

        // Create Orders table.
        DataTable ordersTable = new DataTable("Orders");
        ordersTable.Columns.Add("CustID", typeof(int));
        ordersTable.Columns.Add("CustName", typeof(string));
        ordersTable.Constraints.CollectionChanged +=
            new System.ComponentModel.CollectionChangeEventHandler(
            Collection_Changed);

        // Create unique constraint.
        UniqueConstraint constraint = new UniqueConstraint(
            customersTable.Columns["id"]);
        customersTable.Constraints.Add(constraint);
    
        // Create unique constraint and specify as primary key.
        ordersTable.Constraints.Add(
            "pKey", ordersTable.Columns["CustID"], true);

        // Remove constraints.
        customersTable.Constraints.RemoveAt(0);

        // Results in an Exception. You can't remove
        // a primary key constraint.
        ordersTable.Constraints.RemoveAt(0);
    }
    catch(Exception ex)
    {
        // Process exception and return.
        Console.WriteLine("Exception of type {0} occurred.",
            ex.GetType());
    }
}

private static void Collection_Changed(object sender,
    System.ComponentModel.CollectionChangeEventArgs ex)
{
    Console.WriteLine("List_Changed Event: '{0}'\t element={1}",
        ex.Action, ex.Element);
}

Remarks

For more information about how to handle events, see Handling and Raising Events.

Applies to

Product Versions
.NET Core 2.0, Core 2.1, Core 2.2, Core 3.0, Core 3.1, 5, 6, 7, 8, 9
.NET Framework 1.1, 2.0, 3.0, 3.5, 4.0, 4.5, 4.5.1, 4.5.2, 4.6, 4.6.1, 4.6.2, 4.7, 4.7.1, 4.7.2, 4.8, 4.8.1
.NET Standard 2.0, 2.1