TreeView.DrawNode 事件
定義
重要
部分資訊涉及發行前產品，在發行之前可能會有大幅修改。 Microsoft 對此處提供的資訊，不做任何明確或隱含的瑕疵擔保。
當抽取 a TreeView 且 DrawMode 屬性設定 TreeViewDrawMode 為非 Normal的值時，會發生。
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 事件類型
範例
以下程式碼範例示範如何利用擁有者繪圖來自訂控制項 TreeView 。 TreeView範例中的控制項會顯示可選的節點標籤，與標準節點標籤並列。 節點標籤是透過利用 屬性 TreeNode.Tag 來指定的。 TreeView控制鍵也使用自訂顏色，其中包含自訂的高亮色。
你可以透過設定顏色屬性來自訂大部分 TreeView 顏色，但選取高亮色作為屬性並不可使用。 此外，預設的選取矩形只延伸到節點標籤周圍。 必須使用擁有者繪圖來繪製節點標籤，並繪製一個足夠大的自訂高亮矩形以包含節點標籤。
在範例中，事件的處理器 DrawNode 會手動繪製節點標籤和自訂選取高亮。 未被選取的節點不需要自訂。 對於這些，屬性 DrawTreeNodeEventArgs.DrawDefault 設定為 ， true 讓作業系統會繪製它們。
此外，事件的處理器 MouseDown 也會提供命中測試。 預設情況下，節點只能透過點擊標籤周圍的區域來選擇。 MouseDown事件處理程序會選擇一個節點，該節點會被點擊在任何區域內，或在節點標籤周圍區域內（若有的話）。
#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
備註
利用此事件透過擁有者繪圖自訂控制 TreeView 節點的外觀。
此事件僅在屬性DrawMode值TreeViewDrawModeOwnerDrawAll為 或 OwnerDrawText時才會被觸發。 下表說明了當DrawMode屬性設定為這些值時，如何TreeNode進行自訂。
| DrawMode 屬性值 | TreeNode 自訂 |
|---|---|
| OwnerDrawText | TreeNode標籤區域可以自訂。 其他 TreeNode 元素則自動繪製。 |
| OwnerDrawAll | 整體 TreeNode 外觀可以自訂。 圖示、勾選框、加減號，以及連接節點的線條，若需要，必須手動繪製。 |
如果使用控制項Font屬性指定的TreeView字型繪製，TreeNode.Text該值所佔據的區域即為可點擊節點以選取該節點的區域。 這稱為命中測試區域。 如果你畫在這個區域外，應該提供自己的程式碼，當點擊可見區域時選擇節點。
命中測試區域對應於使用OwnerDrawText時的DrawTreeNodeEventArgs.Bounds性質。 然而，使用 OwnerDrawAll時，該 DrawTreeNodeEventArgs.Bounds 性質涵蓋了整個寬度 TreeView。 在這種情況下，你可以透過取得 DrawTreeNodeEventArgs.Node 該值並存取其 TreeNode.Bounds 屬性來存取命中測試區域。 你可以在這些範圍內繪製節點的命中測試區域，或者提供你自己的命中測試程式碼。 請注意，設定該 TreeNode.NodeFont 屬性不會改變命中測試區域的大小，該大小是使用整個 TreeView的字型計算的。
欲了解更多如何處理事件的資訊，請參閱 「處理與提升事件」。
