Tree Traversal

• Jul 29, 2019
• 5 minutes to read

This topic explains how to traverse vertical and property grid’s rows that are organized into a tree.

Enumerate All Rows

Follow the steps below to enumerate grid rows and perform a custom operation on each row.

• Specify the operation performed on rows.

  • Inherit from the RowOperation abstract class. This class specifies an operation performed on rows.
  • Override the RowOperation.Execute method. This method is called each time a row is enumerated and accepts the row as a parameter.
  C#

  public class MyOperation : RowOperation {
      public override void Execute(BaseRow row) {
          //Do something.
      }
  }
  

  VB.NET

  Public Class MyOperation
      Inherits RowOperation
  
      Public Overrides Sub Execute(row As BaseRow)
          'Do something.
      End Sub
  End Class
  

• Enumerate rows and perform the specified operation on each row.

  • Use the VGridControlBase.RowsIterator property to get an iterator.
  • Pass the created operation to the VGridRowsIterator.DoOperation or VGridRowsIterator.DoLocalOperation method.
  C#

  vGridControl1.RowsIterator.DoOperation(new MyOperation());
  

  VB.NET

  VGridControl1.RowsIterator.DoOperation(New MyOperation())
  

Enumerate Specific Rows

You can also override the operation’s following properties and methods:

• the RowOperation.NeedsFullIteration property (true if not overridden) — gets or sets whether to enumerate all rows or only rows that have child rows (see BaseRow.HasChildren).

  Tip

  Use the RowOperation.NeedsFullIteration property to improve performance. For instance, if the operation expands parent rows, there is no need to enumerate rows that have no child rows.

• the RowOperation.NeedsVisitChildren method (returns true if not overridden) — returns whether to enumerate the specified row’s child rows.

  Tip

  Use the RowOperation.NeedsVisitChildren method to improve performance. For instance, if you need to only iterate root rows.

• the RowOperation.CanContinueIteration method (returns true if not overridden) — called before and after the operation is executed on the current row (passed as the row parameter) and returns whether to continue to enumerate rows.
• the RowOperation.Init method — called before an enumeration.
• the RowOperation.Release method — called after an enumeration.

How to: Count Rows

The following example shows how to count rows:

• Implement a count operation.

  C#

  public class CountOperation : RowOperation {
     int totalRows;
     public CountOperation() : base() {
        totalRows = 0;
     }
     public override void Execute(BaseRow row) {
        totalRows++;
     }
     public int TotalRows { get { return totalRows; } }
  }
  

  VB.NET

  Public Class CountOperation
     Inherits RowOperation
     Dim _TotalRows As Integer
     Public Sub New()
        _TotalRows = 0
     End Sub
     Public Overrides Sub Execute(ByVal Row As BaseRow)
        _TotalRows += 1
     End Sub
     Public ReadOnly Property TotalRows() As Integer
        Get
           Return _TotalRows
        End Get
     End Property
  End Class
  

• Invoke the operation.

  C#

  CountOperation operation = new CountOperation();
  vGridControl1.RowsIterator.DoOperation(operation);
  int totalRows = operation.TotalRows;
  

  VB.NET

  Dim Operation As New CountOperation()
  VGridControl1.RowsIterator.DoOperation(Operation)
  Dim TotalRows As Integer = Operation.TotalRows
  

How to: Obtain Rows at Specific Level

This following example shows how to obtain a collection of rows at the specified level.

C#

public class GetRowsAtLevelOperation : RowOperation {
   int level;
   ArrayList rows;
//The row level
//is initialized in the constructor.
   public GetRowsAtLevelOperation(int level) : base() {
      this.level = level;
      rows = new ArrayList();
   }
//Add a row to the collection
//if it is at the specified level.
   public override void Execute(BaseRow row) {
      if (row.Level == level)
         rows.Add(row);
   }
//Do not enumerate rows
//at higher levels
//to improve performance.
   public override bool NeedsVisitChildren(BaseRow row) {
      if (row.Level == level) 
         return false;
      return true;
   }
   public ArrayList Rows { get { return rows; } }
}

VB.NET

Public Class GetRowsAtLevelOperation
   Inherits RowOperation
   Dim Level As Integer
   Dim _Rows As ArrayList
'The  row level
'is initialized in the constructor.
   Public Sub New(ByVal Level As Integer)
      MyBase.New()
      Me.Level = Level
      _Rows = New ArrayList()
   End Sub
'Add a row to the collection,
'if it is at the specified level.
   Public Overrides Sub Execute(ByVal Row As BaseRow)
      If Row.Level = Level Then
         _Rows.Add(Row)
      End If
   End Sub
'Do not enumerate rows
'at higher levels
'to improve performance.
   Public Overrides Function NeedsVisitChildren(ByVal Row As BaseRow) As Boolean
      If Row.Level = Level Then Return False
      Return True
   End Function
   Public ReadOnly Property Rows() As ArrayList
      Get
         Return _Rows
      End Get
   End Property
End Class

The code below prohibits users to resize rows at the first level.

C#

GetRowsAtLevelOperation operation = new GetRowsAtLevelOperation(1);
vGridControl1.RowsIterator.DoOperation(operation);
foreach (object rowObject in operation.Rows) {
   BaseRow row = rowObject as BaseRow;
   row.Options &= ~VGridOptionsRow.AllowSize;
}

VB.NET

Dim Operation As New GetRowsAtLevelOperation(1)
VGridControl1.RowsIterator.DoOperation(Operation)
Dim RowObject As Object
For Each RowObject In Operation.Rows
   Dim Row As BaseRow = RowObject
   Row.Options = Row.Options And Not VGridOptionsRow.AllowSize
Next

How to: Collapse Specific Rows

The following example shows how to collapse all rows except for the specified row’s parents.

C#

public class CollapseExceptSpecifiedOperation : RowOperation {
   BaseRow visibleRow;
//Specify the row
//in the constructor.
   public CollapseExceptSpecifiedOperation(BaseRow visibleRow) : base() {
      this.visibleRow = visibleRow;
   }
//Collapse a row if it is not
//the specified row's parent.
   public override void Execute(BaseRow row) {
      if (!row.HasAsChild(visibleRow))
         row.Expanded = false;
   }
//Do not enumerate rows
//that have no child rows
//to improve performance.
   public override bool NeedsFullIteration { get { return false; } }
}

VB.NET

Public Class CollapseExceptSpecifiedOperation
   Inherits RowOperation
   Dim VisibleRow As BaseRow
'Specify the row
'in the constructor.
   Public Sub New(ByVal VisibleRow As BaseRow)
      MyBase.New()
      Me.VisibleRow = VisibleRow
   End Sub
'Collapse a row if it is not
'the specified row's parent.
   Public Overrides Sub Execute(ByVal Row As BaseRow)
      If Not Row.HasAsChild(VisibleRow) Then Row.Expanded = False
   End Sub
'Do not enumerate rows
'that have no child rows
‘to improve performance.
   Public Overrides ReadOnly Property NeedsFullIteration() As Boolean
      Get
         Return False
      End Get
   End Property
End Class

The code below collapses all rows except for the focused row’s parents.

C#

vGridControl1.RowsIterator.DoOperation(new CollapseExceptSpecifiedOperation(vGridControl1.FocusedRow));

VB.NET

VGridControl1.RowsIterator.DoOperation(New CollapseExceptSpecifiedOperation(VGridControl1.FocusedRow))