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.NET Framework 4.5.2+
.NET Framework 4.5.2+
.NET Standard 2.0+
.NET Core 3.0+

IObjectSpace.FirstOrDefault<ObjectType>(Expression<Func<ObjectType, Boolean>>) Method

Searches for the first object that matches the specified lambda expression. The generic parameter determines the object’s type.

Namespace: DevExpress.ExpressApp

Assembly: DevExpress.ExpressApp.v21.1.dll

Declaration

ObjectType FirstOrDefault<ObjectType>(
    Expression<Func<ObjectType, bool>> criteriaExpression
)
    where ObjectType : class

Parameters

Name Type Description
criteriaExpression Expression<Func<ObjectType, Boolean>>

A lambda expression to search for an object.

Type Parameters

Name Description
ObjectType

The Type of an object to be returned.

Returns

Type Description
ObjectType

The first object that matches the specified lambda expression.

Remarks

The following example uses a Parametrized Action to search for a Person by LastName. After that, this example invokes the default mail client and creates a new draft of a message for that person.

using DevExpress.ExpressApp;
using DevExpress.ExpressApp.Actions;
using DevExpress.Persistent.Base;
using System.Diagnostics;
// ...
public class SendEmailController : ObjectViewController<ListView, Contact> {
    public SendEmailController() {
        ParametrizedAction sendEmailAction = new ParametrizedAction(
            this, "SendEmail", PredefinedCategory.Edit, typeof(string));
        sendEmailAction.Execute += SendEmailAction_Execute;
    }
    private void SendEmailAction_Execute(object sender, ParametrizedActionExecuteEventArgs e) {
        IObjectSpace objectSpace = View.ObjectSpace;
        string contactParamValue = e.ParameterCurrentValue as string;
        if (!string.IsNullOrEmpty(contactParamValue)) {
            Contact contact = objectSpace.FirstOrDefault<Contact>(p => p.LastName == contactParamValue);
            if (!string.IsNullOrEmpty(contact?.Email)) {
                Process.Start($"mailto:{contact.Email}");
            }
        }
    }
}

Do not implement this method when you implement the IObjectSpace interface in a BaseObjectSpace descendant. The BaseObjectSpace.FirstOrDefault<ObjectType>(Expression<Func<ObjectType, Boolean>>) method invokes a public virtual BaseObjectSpace.FirstOrDefault<ObjectType>(Expression<Func<ObjectType, Boolean>>, Boolean) method. Override the public virtual BaseObjectSpace.FirstOrDefault method to implement an object search.

See Also