public void SetMasterRowExpanded(
    int rowHandle,
    bool expand,
    DetailDescriptorBase descriptor = null
)

Public Sub SetMasterRowExpanded(
    rowHandle As Integer,
    expand As Boolean,
    descriptor As DetailDescriptorBase = Nothing
)

<dxg:GridControl x:Name="grid" AutoGenerateColumns="AddNew" Grid.Column="0">
    <dxg:GridControl.View>
        <dxg:TableView x:Name="view" AutoWidth="True" ShowGroupPanel="False" PreviewKeyDown="TableView_KeyDown"/>
    </dxg:GridControl.View>
    <dxg:GridControl.DetailDescriptor>
        <dxg:DataControlDetailDescriptor ItemsSourcePath="Orders">
            <dxg:DataControlDetailDescriptor.DataControl>
                <dxg:GridControl AutoGenerateColumns="AddNew">
                    <dxg:GridControl.View>
                        <dxg:TableView AutoWidth="True" ShowGroupPanel="False"/>
                    </dxg:GridControl.View>
                </dxg:GridControl>
            </dxg:DataControlDetailDescriptor.DataControl>
        </dxg:DataControlDetailDescriptor>
    </dxg:GridControl.DetailDescriptor>
</dxg:GridControl>

<StackPanel Grid.Column="1" Orientation="Vertical" Margin="10,10,10,10">
    <Button Click="ExpandAll" Content="Expand All" Margin="0,10,0,0"/>
    <Button Click="CollapseAll" Content="Collapse All" Margin="0,10,0,0"/>
    <Button Click="CollapseAllButThis" Content="Collapse All But This" Margin="0,10,0,0"/>
    <TextBlock TextWrapping="Wrap" Margin="0,30,0,0">
        Press <Bold>CTRL+*</Bold> to toggle the focused master row's expanded state.
    </TextBlock>
</StackPanel>

private void TableView_KeyDown(object sender, KeyEventArgs e) {
    TableView view = sender as TableView;

    // Avoid key processing when focus is within detail views or when a group row is focused:
    if (!view.IsFocusedView || view.FocusedRowHandle < 0)
        return;

    // Process CTRL+* key combination:
    if (e.Key == Key.Multiply && ((Keyboard.Modifiers & ModifierKeys.Control) == ModifierKeys.Control)) {
        bool finalExpandedState = !view.Grid.IsMasterRowExpanded(view.FocusedRowHandle);
        view.Grid.SetMasterRowExpanded(view.FocusedRowHandle, finalExpandedState);
        e.Handled = true;
    }
}

void ExpandAll(object sender, RoutedEventArgs e) {
    for (int i = 0; i < grid.VisibleRowCount; i++) {
        var rowHandle = grid.GetRowHandleByVisibleIndex(i);
        grid.ExpandMasterRow(rowHandle);
    }
}

void CollapseAll(object sender, RoutedEventArgs e) {
    for (int i = 0; i < grid.VisibleRowCount; i++) {
        var rowHandle = grid.GetRowHandleByVisibleIndex(i);
        grid.CollapseMasterRow(rowHandle);
    }
}

void CollapseAllButThis(object sender, RoutedEventArgs e) {
    for (int i = 0; i < grid.VisibleRowCount; i++) {
        var rowHandle = grid.GetRowHandleByVisibleIndex(i);
        var detailGrid = grid.GetVisibleDetail(rowHandle);
        if (detailGrid != null) {
            var detailView = ((GridControl)detailGrid).View;
            var focusedDetailRowHandle = ((TableView)detailView).FocusedRowHandle;
            if (focusedDetailRowHandle == DataControlBase.InvalidRowHandle && rowHandle != view.FocusedRowHandle)
                grid.CollapseMasterRow(rowHandle);
        }
    }
}

Private Sub TableView_KeyDown(ByVal sender As Object, ByVal e As KeyEventArgs)
    Dim view As TableView = TryCast(sender, TableView)
    ' Avoid key processing when focus is within detail views or when a group row is focused:
    If Not view.IsFocusedView OrElse view.FocusedRowHandle < 0 Then Return
    ' Process CTRL+* key combination:
    If e.Key = Key.Multiply AndAlso (Keyboard.Modifiers And ModifierKeys.Control) = ModifierKeys.Control Then
        Dim finalExpandedState As Boolean = Not view.Grid.IsMasterRowExpanded(view.FocusedRowHandle)
        view.Grid.SetMasterRowExpanded(view.FocusedRowHandle, finalExpandedState)
        e.Handled = True
    End If
End Sub

Private Sub ExpandAll(ByVal sender As Object, ByVal e As RoutedEventArgs)
    For i As Integer = 0 To Me.grid.VisibleRowCount - 1
        Dim rowHandle = Me.grid.GetRowHandleByVisibleIndex(i)
        Me.grid.ExpandMasterRow(rowHandle)
    Next
End Sub

Private Sub CollapseAll(ByVal sender As Object, ByVal e As RoutedEventArgs)
    For i As Integer = 0 To Me.grid.VisibleRowCount - 1
        Dim rowHandle = Me.grid.GetRowHandleByVisibleIndex(i)
        Me.grid.CollapseMasterRow(rowHandle)
    Next
End Sub

Private Sub CollapseAllButThis(ByVal sender As Object, ByVal e As RoutedEventArgs)
    For i As Integer = 0 To Me.grid.VisibleRowCount - 1
        Dim rowHandle = Me.grid.GetRowHandleByVisibleIndex(i)
        Dim detailGrid = Me.grid.GetVisibleDetail(rowHandle)
        If detailGrid IsNot Nothing Then
            Dim detailView = CType(detailGrid, GridControl).View
            Dim focusedDetailRowHandle = CType(detailView, TableView).FocusedRowHandle
            If focusedDetailRowHandle = DataControlBase.InvalidRowHandle AndAlso rowHandle <> Me.view.FocusedRowHandle Then Me.grid.CollapseMasterRow(rowHandle)
        End If
    Next
End Sub

bool finalExpandedState = !view.Grid.IsMasterRowExpanded(view.FocusedRowHandle);
view.Grid.SetMasterRowExpanded(view.FocusedRowHandle, finalExpandedState);
e.Handled = true;

Dim finalExpandedState As Boolean = Not view.Grid.IsMasterRowExpanded(view.FocusedRowHandle)
view.Grid.SetMasterRowExpanded(view.FocusedRowHandle, finalExpandedState)
e.Handled = True