How to: Implement Error Notifications for Custom Business Object on Data Source Level

• Oct 25, 2019
• 4 minutes to read

The following example demonstrates how to implement error notifications for a custom business object at the data source level, using the IDXDataErrorInfo interface. Error information will be handled by the DXErrorProvider component, which will indicate any error to an end-user.

In this example, the business object is represented by a custom MyRecord class. It contains two properties (FirstName and LastName) that cannot be empty. This class’ records are stored in a BindingSource component and edited using text editors (the FirstName and LastName properties are edited in a textEdit1 and textEdit2 controls respectively).

The requirement is to visually indicate errors within the editors, if the record’s FirstName or LastName property contain an empty string. In this example, the error information is provided on the data source level. The MyRecord class implements the IDXDataErrorInfo interface and returns the error information via the IDXDataErrorInfo.GetPropertyError method. To display the supplied errors within the editors, a DXErrorProvider component needs to be added to the form. It indicates errors as error icons, which can be hovered over to display error text.

To automatically track errors supplied by a data source, the DXErrorProvider component must be bound to this data source via the DXErrorProvider.DataSource property. In this example, the DXErrorProvider.DataSource property is set to the BindingSource.

The following image illustrates the resulting form after it has been opened at runtime. The editors contain empty strings, and as a result error icons are displayed within the editors:

C#

using DevExpress.XtraEditors.DXErrorProvider;

private void Form1_Load(object sender, EventArgs e) {
    // Specifies the type of records stored in the BindingSource.
    bindingSource1.DataSource = typeof(MyRecord);
    // Creates an empty MyRecord and adds it to the BindingSource.
    MyRecord rec = new MyRecord();            
    rec.FirstName = "";
    rec.LastName = "";
    bindingSource1.Add(rec);
    // Binds the text editors to the MyRecord.FirstName and MyRecord.LastName properties.
    textEdit1.DataBindings.Add(new Binding("EditValue", this.bindingSource1, 
      "FirstName", true));
    textEdit2.DataBindings.Add(new Binding("EditValue", this.bindingSource1, 
       "LastName", true));
    // Binds the DXErrorProvider to the data source.
    dxErrorProvider1.DataSource = bindingSource1;
    // Specifies the container of controls (textEdit1 and textEdit2).
    dxErrorProvider1.ContainerControl = this;
}

// A custom record class.
public class MyRecord : IDXDataErrorInfo {
    private string firstName;
    private string lastName;
    public MyRecord() { }
    public string FirstName {
        get { return firstName; }
        set { firstName = value; }
    }
    public string LastName {
        get { return lastName; }
        set { lastName = value; }
    }
    // Implements the IDXDataErrorInfo.GetPropertyError method.
    public void GetPropertyError(string propertyName, ErrorInfo info) {
        if (propertyName == "FirstName" && FirstName == "" ||
            propertyName == "LastName" && LastName == "") {
            info.ErrorText = String.Format("The '{0}' field cannot be empty", propertyName);
        }
    }
    // IDXDataErrorInfo.GetError method
    public void GetError(ErrorInfo info) { }        
}

VB.NET

Imports DevExpress.XtraEditors.DXErrorProvider

Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) _
  Handles MyBase.Load
    ' Specifies the type of records stored in the BindingSource.
    bindingSource1.DataSource = GetType(MyRecord)
    ' Creates an empty MyRecord and adds it to the BindingSource.
    Dim rec As MyRecord = New MyRecord
    rec.FirstName = ""
    rec.LastName = ""
    bindingSource1.Add(rec)
    ' Binds the text editors to the MyRecord.FirstName and MyRecord.LastName properties.
    TextEdit1.DataBindings.Add(New Binding("EditValue", Me.bindingSource1, _
      "FirstName", True))
    TextEdit2.DataBindings.Add(New Binding("EditValue", Me.bindingSource1, _
       "LastName", True))
    ' Binds the DXErrorProvider to the data source.
    DxErrorProvider1.DataSource = bindingSource1
    ' Specifies the container of controls (textEdit1 and textEdit2).
    DxErrorProvider1.ContainerControl = Me
End Sub

' A custom record class.
Public Class MyRecord
    Implements IDXDataErrorInfo

    Private _firstName As String
    Private _lastName As String
    Public Sub New()
        MyBase.New()
    End Sub
    Public Property FirstName() As String
        Get
            Return _firstName
        End Get
        Set(ByVal value As String)
            _firstName = value
        End Set
    End Property
    Public Property LastName() As String
        Get
            Return _lastName
        End Get
        Set(ByVal value As String)
            _lastName = value
        End Set
    End Property

    ' Implements the IDXDataErrorInfo.GetPropertyError method.
    Public Sub GetPropertyError(ByVal propertyName As String, ByVal info As ErrorInfo) _
      Implements IDXDataErrorInfo.GetPropertyError
        If ((propertyName = "FirstName" AndAlso FirstName = "") _
        OrElse (propertyName = "LastName" AndAlso LastName = "")) Then
            info.ErrorText = String.Format("The '{0}' field cannot be empty", propertyName)
        End If
    End Sub

    ' Implements the IDXDataErrorInfo.GetPropertyError method.
    Public Sub GetError(ByVal info As ErrorInfo) Implements IDXDataErrorInfo.GetError
    End Sub
End Class