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TreeView.DrawNode Evento

  • Riferimento

Definizione

Spazio dei nomi:
System.Windows.Forms
Assembly:
System.Windows.Forms.dll

Si verifica quando viene disegnato un oggetto TreeView e la proprietà DrawMode è impostata su un valore di TreeViewDrawMode diverso da Normal.

public:
 event System::Windows::Forms::DrawTreeNodeEventHandler ^ DrawNode;
public event System.Windows.Forms.DrawTreeNodeEventHandler DrawNode;
public event System.Windows.Forms.DrawTreeNodeEventHandler? DrawNode;
member this.DrawNode : System.Windows.Forms.DrawTreeNodeEventHandler 
Public Custom Event DrawNode As DrawTreeNodeEventHandler

Tipo evento

DrawTreeNodeEventHandler

Esempio

Nell'esempio di codice seguente viene illustrato come personalizzare un controllo usando il TreeView disegno del proprietario. Il controllo nell'esempio TreeView visualizza tag di nodo facoltativi insieme alle etichette dei nodi standard. I tag del nodo vengono specificati usando la TreeNode.Tag proprietà . Il TreeView controllo usa anche colori personalizzati, che includono un colore di evidenziazione personalizzato.

È possibile personalizzare la maggior parte dei TreeView colori impostando le proprietà dei colori, ma il colore di evidenziazione della selezione non è disponibile come proprietà. Inoltre, il rettangolo di evidenziazione della selezione predefinito si estende solo intorno a un'etichetta del nodo. Il disegno del proprietario deve essere usato per disegnare i tag del nodo e per disegnare un rettangolo di evidenziazione personalizzato abbastanza grande per includere un tag di nodo.

Nell'esempio, un gestore per l'evento disegna i tag del nodo e l'evidenziazione DrawNode personalizzata della selezione manualmente. I nodi non selezionati non richiedono la personalizzazione. Per queste, la DrawTreeNodeEventArgs.DrawDefault proprietà è impostata su true in modo che vengano disegnate dal sistema operativo.

Inoltre, un gestore per l'evento MouseDown fornisce hit test. Per impostazione predefinita, un nodo può essere selezionato solo facendo clic sull'area intorno alla relativa etichetta. Il MouseDown gestore eventi seleziona un nodo che viene fatto clic ovunque all'interno di questa area o all'interno dell'area intorno a un tag di nodo, se presente.

#using <System.dll>
#using <System.Windows.Forms.dll>
#using <System.Drawing.dll>

using namespace System;
using namespace System::Drawing;
using namespace System::Windows::Forms;
public ref class TreeViewOwnerDraw: public Form
{
private:
   TreeView^ myTreeView;

   // Create a Font object for the node tags.
   System::Drawing::Font^ tagFont;

public:

   TreeViewOwnerDraw()
   {
      tagFont = gcnew System::Drawing::Font( "Helvetica",8,FontStyle::Bold );

      // Create and initialize the TreeView control.
      myTreeView = gcnew TreeView;
      myTreeView->Dock = DockStyle::Fill;
      myTreeView->BackColor = Color::Tan;
      myTreeView->CheckBoxes = true;
      
      // Add nodes to the TreeView control.
      TreeNode^ node;
      for ( int x = 1; x < 4; ++x )
      {
         // Add a root node to the TreeView control.
         node = myTreeView->Nodes->Add( String::Format( "Task {0}", x ) );
         for ( int y = 1; y < 4; ++y )
         {
            // Add a child node to the root node.
            node->Nodes->Add( String::Format( "Subtask {0}", y ) );
         }
      }
      myTreeView->ExpandAll();
      
      // Add tags containing alert messages to a few nodes 
      // and set the node background color to highlight them.
      myTreeView->Nodes[ 1 ]->Nodes[ 0 ]->Tag = "urgent!";
      myTreeView->Nodes[ 1 ]->Nodes[ 0 ]->BackColor = Color::Yellow;
      myTreeView->SelectedNode = myTreeView->Nodes[ 1 ]->Nodes[ 0 ];
      myTreeView->Nodes[ 2 ]->Nodes[ 1 ]->Tag = "urgent!";
      myTreeView->Nodes[ 2 ]->Nodes[ 1 ]->BackColor = Color::Yellow;
      
      // Configure the TreeView control for owner-draw and add
      // a handler for the DrawNode event.
      myTreeView->DrawMode = TreeViewDrawMode::OwnerDrawText;
      myTreeView->DrawNode += gcnew DrawTreeNodeEventHandler( this, &TreeViewOwnerDraw::myTreeView_DrawNode );
      
      // Add a handler for the MouseDown event so that a node can be 
      // selected by clicking the tag text as well as the node text.
      myTreeView->MouseDown += gcnew MouseEventHandler( this, &TreeViewOwnerDraw::myTreeView_MouseDown );
      
      // Initialize the form and add the TreeView control to it.
      this->ClientSize = System::Drawing::Size( 292, 273 );
      this->Controls->Add( myTreeView );
   }

protected:
   // Clean up any resources being used.        
   ~TreeViewOwnerDraw()
   {
      if ( tagFont != nullptr )
      {
         delete tagFont;
      }
   }

   // Draws a node.
private:
   void myTreeView_DrawNode( Object^ sender, DrawTreeNodeEventArgs^ e )
   {
      // Draw the background and node text for a selected node.
      if ( (e->State & TreeNodeStates::Selected) != (TreeNodeStates)0 )
      {
         // Draw the background of the selected node. The NodeBounds
         // method makes the highlight rectangle large enough to
         // include the text of a node tag, if one is present.
         e->Graphics->FillRectangle( Brushes::Green, NodeBounds( e->Node ) );

         // Retrieve the node font. If the node font has not been set,
         // use the TreeView font.
         System::Drawing::Font^ nodeFont = e->Node->NodeFont;
         if ( nodeFont == nullptr )
                  nodeFont = (dynamic_cast<TreeView^>(sender))->Font;

         // Draw the node text.
         e->Graphics->DrawString( e->Node->Text, nodeFont, Brushes::White, Rectangle::Inflate( e->Bounds, 2, 0 ) );
      }
      // Use the default background and node text.
      else
      {
         e->DrawDefault = true;
      }

      // If a node tag is present, draw its string representation 
      // to the right of the label text.
      if ( e->Node->Tag != nullptr )
      {
         e->Graphics->DrawString( e->Node->Tag->ToString(), tagFont, Brushes::Yellow, (float)e->Bounds.Right + 2, (float)e->Bounds.Top );
      }

      
      // If the node has focus, draw the focus rectangle large, making
      // it large enough to include the text of the node tag, if present.
      if ( (e->State & TreeNodeStates::Focused) != (TreeNodeStates)0 )
      {
         Pen^ focusPen = gcnew Pen( Color::Black );
         try
         {
            focusPen->DashStyle = System::Drawing::Drawing2D::DashStyle::Dot;
            Rectangle focusBounds = NodeBounds( e->Node );
            focusBounds.Size = System::Drawing::Size( focusBounds.Width - 1, focusBounds.Height - 1 );
            e->Graphics->DrawRectangle( focusPen, focusBounds );
         }
         finally
         {
            if ( focusPen )
               delete safe_cast<IDisposable^>(focusPen);
         }

      }
   }

   // Selects a node that is clicked on its label or tag text.
   void myTreeView_MouseDown( Object^ /*sender*/, MouseEventArgs^ e )
   {
      TreeNode^ clickedNode = myTreeView->GetNodeAt( e->X, e->Y );
      if ( NodeBounds( clickedNode ).Contains( e->X, e->Y ) )
      {
         myTreeView->SelectedNode = clickedNode;
      }
   }

   // Returns the bounds of the specified node, including the region 
   // occupied by the node label and any node tag displayed.
   Rectangle NodeBounds( TreeNode^ node )
   {
      // Set the return value to the normal node bounds.
      Rectangle bounds = node->Bounds;
      if ( node->Tag != nullptr )
      {
         // Retrieve a Graphics object from the TreeView handle
         // and use it to calculate the display width of the tag.
         Graphics^ g = myTreeView->CreateGraphics();
         int tagWidth = (int)g->MeasureString( node->Tag->ToString(), tagFont ).Width + 6;
         
         // Adjust the node bounds using the calculated value.
         bounds.Offset( tagWidth / 2, 0 );
         bounds = Rectangle::Inflate( bounds, tagWidth / 2, 0 );
         g->~Graphics();
      }

      return bounds;
   }
};

[STAThreadAttribute]
int main()
{
   Application::Run( gcnew TreeViewOwnerDraw );
}

using System;
using System.Drawing;
using System.Windows.Forms;

public class TreeViewOwnerDraw : Form
{
    private TreeView myTreeView;

    // Create a Font object for the node tags.
    Font tagFont = new Font("Helvetica", 8, FontStyle.Bold);

    public TreeViewOwnerDraw()
    {
        // Create and initialize the TreeView control.
        myTreeView = new TreeView();
        myTreeView.Dock = DockStyle.Fill;
        myTreeView.BackColor = Color.Tan;
        myTreeView.CheckBoxes = true;

        // Add nodes to the TreeView control.
        TreeNode node;
        for (int x = 1; x < 4; ++x)
        {
            // Add a root node to the TreeView control.
            node = myTreeView.Nodes.Add(String.Format("Task {0}", x));
            for (int y = 1; y < 4; ++y)
            {
                // Add a child node to the root node.
                node.Nodes.Add(String.Format("Subtask {0}", y));
            }
        }
        myTreeView.ExpandAll();

        // Add tags containing alert messages to a few nodes 
        // and set the node background color to highlight them.
        myTreeView.Nodes[1].Nodes[0].Tag = "urgent!";
        myTreeView.Nodes[1].Nodes[0].BackColor = Color.Yellow;
        myTreeView.SelectedNode = myTreeView.Nodes[1].Nodes[0];
        myTreeView.Nodes[2].Nodes[1].Tag = "urgent!";
        myTreeView.Nodes[2].Nodes[1].BackColor = Color.Yellow;

        // Configure the TreeView control for owner-draw and add
        // a handler for the DrawNode event.
        myTreeView.DrawMode = TreeViewDrawMode.OwnerDrawText;
        myTreeView.DrawNode += 
            new DrawTreeNodeEventHandler(myTreeView_DrawNode);

        // Add a handler for the MouseDown event so that a node can be 
        // selected by clicking the tag text as well as the node text.
        myTreeView.MouseDown += new MouseEventHandler(myTreeView_MouseDown);

        // Initialize the form and add the TreeView control to it.
        this.ClientSize = new Size(292, 273);
        this.Controls.Add(myTreeView);
    }

    // Clean up any resources being used.        
    protected override void Dispose(bool disposing)
    {
        if (disposing)
        {
            tagFont.Dispose();
        }
        base.Dispose(disposing);
    }

    [STAThreadAttribute()]
    static void Main() 
    {
        Application.Run(new TreeViewOwnerDraw());
    }

    // Draws a node.
    private void myTreeView_DrawNode(
        object sender, DrawTreeNodeEventArgs e)
    {
        // Draw the background and node text for a selected node.
        if ((e.State & TreeNodeStates.Selected) != 0)
        {
            // Draw the background of the selected node. The NodeBounds
            // method makes the highlight rectangle large enough to
            // include the text of a node tag, if one is present.
            e.Graphics.FillRectangle(Brushes.Green, NodeBounds(e.Node));

            // Retrieve the node font. If the node font has not been set,
            // use the TreeView font.
            Font nodeFont = e.Node.NodeFont;
            if (nodeFont == null) nodeFont = ((TreeView)sender).Font;

            // Draw the node text.
            e.Graphics.DrawString(e.Node.Text, nodeFont, Brushes.White,
                Rectangle.Inflate(e.Bounds, 2, 0));
        }

        // Use the default background and node text.
        else 
        {
            e.DrawDefault = true;
        }

        // If a node tag is present, draw its string representation 
        // to the right of the label text.
        if (e.Node.Tag != null)
        {
            e.Graphics.DrawString(e.Node.Tag.ToString(), tagFont,
                Brushes.Yellow, e.Bounds.Right + 2, e.Bounds.Top);
        }

        // If the node has focus, draw the focus rectangle large, making
        // it large enough to include the text of the node tag, if present.
        if ((e.State & TreeNodeStates.Focused) != 0)
        {
            using (Pen focusPen = new Pen(Color.Black))
            {
                focusPen.DashStyle = System.Drawing.Drawing2D.DashStyle.Dot;
                Rectangle focusBounds = NodeBounds(e.Node);
                focusBounds.Size = new Size(focusBounds.Width - 1, 
                focusBounds.Height - 1);
                e.Graphics.DrawRectangle(focusPen, focusBounds);
            }
        }
    }

    // Selects a node that is clicked on its label or tag text.
    private void myTreeView_MouseDown(object sender, MouseEventArgs e)
    {
        TreeNode clickedNode = myTreeView.GetNodeAt(e.X, e.Y);
        if (NodeBounds(clickedNode).Contains(e.X, e.Y))
        {
            myTreeView.SelectedNode = clickedNode;
        }
    }

    // Returns the bounds of the specified node, including the region 
    // occupied by the node label and any node tag displayed.
    private Rectangle NodeBounds(TreeNode node)
    {
        // Set the return value to the normal node bounds.
        Rectangle bounds = node.Bounds;
        if (node.Tag != null)
        {
            // Retrieve a Graphics object from the TreeView handle
            // and use it to calculate the display width of the tag.
            Graphics g = myTreeView.CreateGraphics(); 
            int tagWidth = (int)g.MeasureString
                (node.Tag.ToString(), tagFont).Width + 6;

            // Adjust the node bounds using the calculated value.
            bounds.Offset(tagWidth/2, 0);
            bounds = Rectangle.Inflate(bounds, tagWidth/2, 0);
            g.Dispose();
         }
        
        return bounds;
    }
}

Imports System.Drawing
Imports System.Windows.Forms

Public Class TreeViewOwnerDraw
    Inherits Form

    Private WithEvents myTreeView As TreeView
    
    ' Create a Font object for the node tags.
    Private tagFont As New Font("Helvetica", 8, FontStyle.Bold)
    
    Public Sub New()

        ' Create and initialize the TreeView control.
        myTreeView = New TreeView()
        myTreeView.Dock = DockStyle.Fill
        myTreeView.BackColor = Color.Tan
        myTreeView.CheckBoxes = True
        
        ' Add nodes to the TreeView control.
        Dim node As TreeNode
        Dim x As Integer
        For x = 1 To 3

            ' Add a root node to the TreeView control.
            node = myTreeView.Nodes.Add(String.Format("Task {0}", x))
            Dim y As Integer
            For y = 1 To 3 

                ' Add a child node to the root node.
                node.Nodes.Add(String.Format("Subtask {0}", y))
            Next y
        Next x
        myTreeView.ExpandAll()
        
        ' Add tags containing alert messages to a few nodes 
        ' and set the node background color to highlight them.
        myTreeView.Nodes(1).Nodes(0).Tag = "urgent!"
        myTreeView.Nodes(1).Nodes(0).BackColor = Color.Yellow
        myTreeView.SelectedNode = myTreeView.Nodes(1).Nodes(0)
        myTreeView.Nodes(2).Nodes(1).Tag = "urgent!"
        myTreeView.Nodes(2).Nodes(1).BackColor = Color.Yellow
        
        ' Configure the TreeView control for owner-draw.
        myTreeView.DrawMode = TreeViewDrawMode.OwnerDrawText

        ' Add a handler for the MouseDown event so that a node can be 
        ' selected by clicking the tag text as well as the node text.
        AddHandler myTreeView.MouseDown, AddressOf myTreeView_MouseDown
        
        ' Initialize the form and add the TreeView control to it.
        Me.ClientSize = New Size(292, 273)
        Me.Controls.Add(myTreeView)
    End Sub
    
    <STAThreadAttribute()> _
    Shared Sub Main()
        Application.Run(New TreeViewOwnerDraw())
    End Sub
    
    ' Draws a node.
    Private Sub myTreeView_DrawNode(ByVal sender As Object, _
        ByVal e As DrawTreeNodeEventArgs) Handles myTreeView.DrawNode

        ' Draw the background and node text for a selected node.
        If (e.State And TreeNodeStates.Selected) <> 0 Then

            ' Draw the background of the selected node. The NodeBounds
            ' method makes the highlight rectangle large enough to
            ' include the text of a node tag, if one is present.
            e.Graphics.FillRectangle(Brushes.Green, NodeBounds(e.Node))

            ' Retrieve the node font. If the node font has not been set,
            ' use the TreeView font.
            Dim nodeFont As Font = e.Node.NodeFont
            If nodeFont Is Nothing Then
                nodeFont = CType(sender, TreeView).Font
            End If

            ' Draw the node text.
            e.Graphics.DrawString(e.Node.Text, nodeFont, Brushes.White, _
                e.Bounds.Left - 2, e.Bounds.Top)

        ' Use the default background and node text.
        Else
            e.DrawDefault = True
        End If

        ' If a node tag is present, draw its string representation 
        ' to the right of the label text.
        If (e.Node.Tag IsNot Nothing) Then
            e.Graphics.DrawString(e.Node.Tag.ToString(), tagFont, _
                Brushes.Yellow, e.Bounds.Right + 2, e.Bounds.Top)
        End If

        ' If the node has focus, draw the focus rectangle large, making
        ' it large enough to include the text of the node tag, if present.
        If (e.State And TreeNodeStates.Focused) <> 0 Then
            Dim focusPen As New Pen(Color.Black)
            Try
                focusPen.DashStyle = System.Drawing.Drawing2D.DashStyle.Dot
                Dim focusBounds As Rectangle = NodeBounds(e.Node)
                focusBounds.Size = New Size(focusBounds.Width - 1, _
                    focusBounds.Height - 1)
                e.Graphics.DrawRectangle(focusPen, focusBounds)
            Finally
                focusPen.Dispose()
            End Try
        End If

    End Sub

    ' Selects a node that is clicked on its label or tag text.
    Private Sub myTreeView_MouseDown(ByVal sender As Object, ByVal e As MouseEventArgs)
        Dim clickedNode As TreeNode = myTreeView.GetNodeAt(e.X, e.Y)
        If NodeBounds(clickedNode).Contains(e.X, e.Y) Then
            myTreeView.SelectedNode = clickedNode
        End If
    End Sub

    ' Returns the bounds of the specified node, including the region 
    ' occupied by the node label and any node tag displayed.
    Private Function NodeBounds(ByVal node As TreeNode) As Rectangle

        ' Set the return value to the normal node bounds.
        Dim bounds As Rectangle = node.Bounds
        If (node.Tag IsNot Nothing) Then

            ' Retrieve a Graphics object from the TreeView handle
            ' and use it to calculate the display width of the tag.
            Dim g As Graphics = myTreeView.CreateGraphics()
            Dim tagWidth As Integer = CInt(g.MeasureString( _
                node.Tag.ToString(), tagFont).Width) + 6

            ' Adjust the node bounds using the calculated value.
            bounds.Offset(tagWidth \ 2, 0)
            bounds = Rectangle.Inflate(bounds, tagWidth \ 2, 0)
            g.Dispose()
        End If
        Return bounds
    End Function 'NodeBounds

End Class

Commenti

Usare questo evento per personalizzare l'aspetto dei nodi in un TreeView controllo usando il disegno del proprietario.

Questo evento viene generato solo quando la DrawMode proprietà è impostata su TreeViewDrawMode valori di OwnerDrawAll o OwnerDrawText. La tabella seguente indica come è possibile personalizzare la TreeNode proprietà quando la DrawMode proprietà è impostata su questi valori.

Valore della proprietà DrawMode Personalizzazione di TreeNode
OwnerDrawText L'area dell'etichetta TreeNode può essere personalizzata. Tutti gli altri TreeNode elementi vengono disegnati automaticamente.
OwnerDrawAll L'aspetto dell'intero TreeNode può essere personalizzato. Le icone, le caselle di controllo e i segni meno e le righe che collegano i nodi devono essere disegnate manualmente se desiderate.

L'area che il TreeNode.Text valore occupa se fosse stato disegnato usando il tipo di carattere specificato dalla TreeView proprietà del Font controllo è l'area in cui è possibile fare clic su un nodo per selezionarla. Viene chiamata area di hit test. Se si disegna all'esterno di questa area, è necessario specificare il proprio codice che seleziona un nodo quando viene fatto clic sulla relativa area visibile.

L'area DrawTreeNodeEventArgs.Bounds di hit test corrisponde alla proprietà quando si usa OwnerDrawText. Quando si usa OwnerDrawAll, tuttavia, la DrawTreeNodeEventArgs.Bounds proprietà include l'intera larghezza di TreeView. In questo caso, è possibile accedere all'area di hit test ottenendo il DrawTreeNodeEventArgs.Node valore e accedendo alla relativa TreeNode.Bounds proprietà. È quindi possibile disegnare l'area di hit test del nodo all'interno di questi limiti oppure specificare il proprio codice di hit test. Si noti che l'impostazione della TreeNode.NodeFont proprietà non modifica le dimensioni dell'area di hit test, calcolata usando il tipo di carattere specificato per l'intero TreeViewoggetto .

Per altre informazioni su come gestire gli eventi, vedere la gestione e generazione di eventi.

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