TreeList.BeforeCheckNode Event

Occurs before a node’s check state is changed.

Namespace: DevExpress.XtraTreeList

Assembly: DevExpress.XtraTreeList.v18.2.dll

Declaration

C#

public event CheckNodeEventHandler BeforeCheckNode

VB.NET

Public Event BeforeCheckNode As CheckNodeEventHandler

Event Data

The BeforeCheckNode event's data class is DevExpress.XtraTreeList.CheckNodeEventArgs.

Remarks

The BeforeCheckNode event is raised when an end-user changes a node’s check state, and allows you to cancel the operation or specify the required check state.

To cancel the operation, set the event parameter’s CanCheck property to false. The previous and current node states are returned by the PrevState and State properties, respectively. You can change the State property’s value to specify the required node state.

The following code prevents an end-user from setting nodes to an indeterminate state.

C#

private void treeList1_BeforeCheckNode(object sender, DevExpress.XtraTreeList.CheckNodeEventArgs e) {
    if (e.State == CheckState.Indeterminate)
        e.State = (e.PrevState == CheckState.Checked ? CheckState.Unchecked : CheckState.Checked);
}

VB.NET

Private Sub TreeList1_BeforeCheckNode(sender As System.Object, e As DevExpress.XtraTreeList.CheckNodeEventArgs) _
Handles TreeList1.BeforeCheckNode
    If e.State = CheckState.Indeterminate Then
        If e.PrevState = CheckState.Checked Then
            e.State = (CheckState.Unchecked)
        Else
            e.State = (CheckState.Checked)
        End If
    End If
End Sub

After a node’s state has been changed, the TreeList.AfterCheckNode event is raised.

See Node Checking - Checkboxes and Radio Buttons to learn more.

Related GitHub Examples

The following code snippets (auto-collected from DevExpress Examples) contain references to the BeforeCheckNode event.

Note

The algorithm used to collect these code examples remains a work in progress. Accordingly, the links and snippets below may produce inaccurate results. If you encounter an issue with code examples below, please use the feedback form on this page to report the issue.

C#

how-to-show-checkboxes-for-only-a-specific-level-e2810/CS/WindowsApplication1/Form1.cs#L55

    treeList.CustomDrawNodeCheckBox += treeList_CustomDrawNodeCheckBox;
    treeList.BeforeCheckNode += treeList_BeforeCheckNode;
}

how-to-modify-the-default-checking-nodes-behavior-in-the-treelist-control-t590828/CS/Example/TreeListCheckHelper.cs#L16

    treeList.OptionsBehavior.AllowIndeterminateCheckState = false;
    treeList.BeforeCheckNode += treeList1_BeforeCheckNode;
}

VB.NET

how-to-show-checkboxes-for-only-a-specific-level-e2810/VB/WindowsApplication1/Form1.vb#L61

    AddHandler treeList.CustomDrawNodeCheckBox, AddressOf treeList_CustomDrawNodeCheckBox
    AddHandler treeList.BeforeCheckNode, AddressOf treeList_BeforeCheckNode
End Sub

how-to-modify-the-default-checking-nodes-behavior-in-the-treelist-control-t590828/VB/Example/TreeListCheckHelper.vb#L14

    treeList.OptionsBehavior.AllowIndeterminateCheckState = False
    AddHandler treeList.BeforeCheckNode, AddressOf treeList1_BeforeCheckNode
End Sub