ComboBox.MeasureItem 事件
每次当需要描述一个所有者描述的 ComboBox 项，并且当列表项的大小已确定时就会发生。
**命名空间:**System.Windows.Forms
**程序集:**System.Windows.Forms（在 system.windows.forms.dll 中）
语法
声明
Public Event MeasureItem As MeasureItemEventHandler
用法
Dim instance As ComboBox
Dim handler As MeasureItemEventHandler
AddHandler instance.MeasureItem, handler
public event MeasureItemEventHandler MeasureItem
public:
event MeasureItemEventHandler^ MeasureItem {
void add (MeasureItemEventHandler^ value);
void remove (MeasureItemEventHandler^ value);
}
/** @event */
public void add_MeasureItem (MeasureItemEventHandler value)
/** @event */
public void remove_MeasureItem (MeasureItemEventHandler value)
JScript 支持使用事件，但不支持进行新的声明。
备注
可以为该事件创建事件处理程序，以在 DrawItem 事件中绘制项之前指定该项的大小。
有关处理事件的更多信息，请参见 使用事件。
示例
下面的代码示例演示如何创建所有者描述的组合框，具体方法为将 DrawMode 属性设置为 OwnerDrawnVariable，并处理 DrawItem 和 MeasureItem 事件。它还阐释了如何设置 DropDownWidth 和 DropDownStyle 属性。要运行该示例，请将以下代码粘贴到一个窗体中。在该窗体的构造函数或 Load 事件中调用 InitializeComboBox 方法。
Friend WithEvents ComboBox1 As System.Windows.Forms.ComboBox
Private animals() As String
' This method initializes the owner-drawn combo box.
' The drop-down width is set much wider than the size of the combo box
' to accomodate the large items in the list. The drop-down style is set to
' ComboBox.DropDown, which requires the user to click on the arrow to
' see the list.
Private Sub InitializeComboBox()
Me.ComboBox1 = New ComboBox
Me.ComboBox1.DrawMode = System.Windows.Forms.DrawMode.OwnerDrawVariable
Me.ComboBox1.Location = New System.Drawing.Point(10, 20)
Me.ComboBox1.Name = "ComboBox1"
Me.ComboBox1.Size = New System.Drawing.Size(100, 120)
Me.ComboBox1.DropDownWidth = 250
Me.ComboBox1.TabIndex = 0
Me.ComboBox1.DropDownStyle = ComboBoxStyle.DropDown
animals = New String() {"Elephant", "c r o c o d i l e", "lion"}
ComboBox1.DataSource = animals
Me.Controls.Add(Me.ComboBox1)
End Sub
' If you set the Draw property to DrawMode.OwnerDrawVariable,
' you must handle the MeasureItem event. This event handler
' will set the height and width of each item before it is drawn.
Private Sub ComboBox1_MeasureItem(ByVal sender As Object, _
ByVal e As System.Windows.Forms.MeasureItemEventArgs) _
Handles ComboBox1.MeasureItem
Select Case e.Index
Case 0
e.ItemHeight = 45
Case 1
e.ItemHeight = 20
Case 2
e.ItemHeight = 35
End Select
e.ItemWidth = 260
End Sub
' You must handle the DrawItem event for owner-drawn combo boxes.
' This event handler changes the color, size and font of an
' item based on its position in the array.
Private Sub ComboBox1_DrawItem(ByVal sender As Object, _
ByVal e As System.Windows.Forms.DrawItemEventArgs) _
Handles ComboBox1.DrawItem
Dim size As Single
Dim myFont As System.Drawing.Font
Dim family As FontFamily
Dim animalColor As New System.Drawing.Color
Select Case e.Index
Case 0
size = 30
animalColor = System.Drawing.Color.Gray
family = FontFamily.GenericSansSerif
Case 1
size = 10
animalColor = System.Drawing.Color.LawnGreen
family = FontFamily.GenericMonospace
Case 2
size = 15
animalColor = System.Drawing.Color.Tan
family = FontFamily.GenericSansSerif
End Select
' Draw the background of the item.
e.DrawBackground()
' Create a square filled with the animals color. Vary the size
' of the rectangle based on the length of the animals name.
Dim rectangle As Rectangle = New Rectangle(2, e.Bounds.Top + 2, _
e.Bounds.Height, e.Bounds.Height - 4)
e.Graphics.FillRectangle(New SolidBrush(animalColor), rectangle)
' Draw each string in the array, using a different size, color,
' and font for each item.
myFont = New Font(family, size, FontStyle.Bold)
e.Graphics.DrawString(animals(e.Index), myFont, System.Drawing.Brushes.Black, _
New RectangleF(e.Bounds.X + rectangle.Width, e.Bounds.Y, _
e.Bounds.Width, e.Bounds.Height))
' Draw the focus rectangle if the mouse hovers over an item.
e.DrawFocusRectangle()
End Sub
internal System.Windows.Forms.ComboBox ComboBox1;
private string[] animals;
// This method initializes the owner-drawn combo box.
// The drop-down width is set much wider than the size of the combo box
// to accomodate the large items in the list. The drop-down style is set to
// ComboBox.DropDown, which requires the user to click on the arrow to
// see the list.
private void InitializeComboBox()
{
this.ComboBox1 = new ComboBox();
this.ComboBox1.DrawMode =
System.Windows.Forms.DrawMode.OwnerDrawVariable;
this.ComboBox1.Location = new System.Drawing.Point(10, 20);
this.ComboBox1.Name = "ComboBox1";
this.ComboBox1.Size = new System.Drawing.Size(100, 120);
this.ComboBox1.DropDownWidth = 250;
this.ComboBox1.TabIndex = 0;
this.ComboBox1.DropDownStyle = ComboBoxStyle.DropDown;
animals = new string[]{"Elephant", "c r o c o d i l e", "lion"};
ComboBox1.DataSource = animals;
this.Controls.Add(this.ComboBox1);
// Hook up the MeasureItem and DrawItem events
this.ComboBox1.DrawItem +=
new DrawItemEventHandler(ComboBox1_DrawItem);
this.ComboBox1.MeasureItem +=
new MeasureItemEventHandler(ComboBox1_MeasureItem);
}
// If you set the Draw property to DrawMode.OwnerDrawVariable,
// you must handle the MeasureItem event. This event handler
// will set the height and width of each item before it is drawn.
private void ComboBox1_MeasureItem(object sender,
System.Windows.Forms.MeasureItemEventArgs e)
{
switch(e.Index)
{
case 0:
e.ItemHeight = 45;
break;
case 1:
e.ItemHeight = 20;
break;
case 2:
e.ItemHeight = 35;
break;
}
e.ItemWidth = 260;
}
// You must handle the DrawItem event for owner-drawn combo boxes.
// This event handler changes the color, size and font of an
// item based on its position in the array.
private void ComboBox1_DrawItem(object sender,
System.Windows.Forms.DrawItemEventArgs e)
{
float size = 0;
System.Drawing.Font myFont;
FontFamily family = null;
System.Drawing.Color animalColor = new System.Drawing.Color();
switch(e.Index)
{
case 0:
size = 30;
animalColor = System.Drawing.Color.Gray;
family = FontFamily.GenericSansSerif;
break;
case 1:
size = 10;
animalColor = System.Drawing.Color.LawnGreen;
family = FontFamily.GenericMonospace;
break;
case 2:
size = 15;
animalColor = System.Drawing.Color.Tan;
family = FontFamily.GenericSansSerif;
break;
}
// Draw the background of the item.
e.DrawBackground();
// Create a square filled with the animals color. Vary the size
// of the rectangle based on the length of the animals name.
Rectangle rectangle = new Rectangle(2, e.Bounds.Top+2,
e.Bounds.Height, e.Bounds.Height-4);
e.Graphics.FillRectangle(new SolidBrush(animalColor), rectangle);
// Draw each string in the array, using a different size, color,
// and font for each item.
myFont = new Font(family, size, FontStyle.Bold);
e.Graphics.DrawString(animals[e.Index], myFont, System.Drawing.Brushes.Black, new RectangleF(e.Bounds.X+rectangle.Width, e.Bounds.Y, e.Bounds.Width, e.Bounds.Height));
// Draw the focus rectangle if the mouse hovers over an item.
e.DrawFocusRectangle();
}
internal:
System::Windows::Forms::ComboBox^ ComboBox1;
private:
array<String^>^ animals;
// This method initializes the owner-drawn combo box.
// The drop-down width is set much wider than the size of the combo box
// to accomodate the large items in the list. The drop-down style is set to
// ComboBox.DropDown, which requires the user to click on the arrow to
// see the list.
void InitializeComboBox()
{
this->ComboBox1 = gcnew ComboBox;
this->ComboBox1->DrawMode = System::Windows::Forms::DrawMode::OwnerDrawVariable;
this->ComboBox1->Location = System::Drawing::Point( 10, 20 );
this->ComboBox1->Name = "ComboBox1";
this->ComboBox1->Size = System::Drawing::Size( 100, 120 );
this->ComboBox1->DropDownWidth = 250;
this->ComboBox1->TabIndex = 0;
this->ComboBox1->DropDownStyle = ComboBoxStyle::DropDown;
animals = gcnew array<String^>{"Elephant","c r o c o d i l e","lion"};
ComboBox1->DataSource = animals;
this->Controls->Add( this->ComboBox1 );
// Hook up the MeasureItem and DrawItem events
this->ComboBox1->DrawItem +=
gcnew DrawItemEventHandler( this, &Form1::ComboBox1_DrawItem );
this->ComboBox1->MeasureItem +=
gcnew MeasureItemEventHandler( this, &Form1::ComboBox1_MeasureItem );
}
// If you set the Draw property to DrawMode.OwnerDrawVariable,
// you must handle the MeasureItem event. This event handler
// will set the height and width of each item before it is drawn.
private:
void ComboBox1_MeasureItem( Object^ sender,
System::Windows::Forms::MeasureItemEventArgs^ e )
{
switch ( e->Index )
{
case 0:
e->ItemHeight = 45;
break;
case 1:
e->ItemHeight = 20;
break;
case 2:
e->ItemHeight = 35;
break;
}
e->ItemWidth = 260;
}
private:
// You must handle the DrawItem event for owner-drawn combo boxes.
// This event handler changes the color, size and font of an
// item based on its position in the array.
void ComboBox1_DrawItem( Object^ sender,
System::Windows::Forms::DrawItemEventArgs^ e )
{
float size = 0;
System::Drawing::Font^ myFont;
FontFamily^ family = nullptr;
System::Drawing::Color animalColor;
switch ( e->Index )
{
case 0:
size = 30;
animalColor = System::Drawing::Color::Gray;
family = FontFamily::GenericSansSerif;
break;
case 1:
size = 10;
animalColor = System::Drawing::Color::LawnGreen;
family = FontFamily::GenericMonospace;
break;
case 2:
size = 15;
animalColor = System::Drawing::Color::Tan;
family = FontFamily::GenericSansSerif;
break;
}
// Draw the background of the item.
e->DrawBackground();
// Create a square filled with the animals color. Vary the size
// of the rectangle based on the length of the animals name.
Rectangle rectangle = Rectangle( 2, e->Bounds.Top + 2,
e->Bounds.Height, e->Bounds.Height - 4 );
e->Graphics->FillRectangle( gcnew SolidBrush( animalColor ), rectangle );
// Draw each string in the array, using a different size, color,
// and font for each item.
myFont = gcnew System::Drawing::Font( family, size, FontStyle::Bold );
e->Graphics->DrawString( animals[ e->Index ], myFont,
System::Drawing::Brushes::Black, RectangleF(
e->Bounds.X + rectangle.Width, e->Bounds.Y,
e->Bounds.Width, e->Bounds.Height) );
// Draw the focus rectangle if the mouse hovers over an item.
e->DrawFocusRectangle();
}
System.Windows.Forms.ComboBox comboBox1;
private String animals[];
// This method initializes the owner-drawn combo box.
// The drop-down width is set much wider than the size of the combo box
// to accomodate the large items in the list. The drop-down style is set to
// ComboBox.DropDown, which requires the user to click on the arrow to
// see the list.
private void InitializeComboBox()
{
this.comboBox1 = new ComboBox();
this.comboBox1.set_DrawMode(
System.Windows.Forms.DrawMode.OwnerDrawVariable);
this.comboBox1.set_Location(new System.Drawing.Point(10, 20));
this.comboBox1.set_Name("comboBox1");
this.comboBox1.set_Size(new System.Drawing.Size(100, 120));
this.comboBox1.set_DropDownWidth(250);
this.comboBox1.set_TabIndex(0);
this.comboBox1.set_DropDownStyle(ComboBoxStyle.DropDown);
animals = new String[] { "Elephant", "c r o c o d i l e", "lion" };
comboBox1.set_DataSource(animals);
this.get_Controls().Add(this.comboBox1);
// Hook up the MeasureItem and DrawItem events
this.comboBox1.add_DrawItem(
new DrawItemEventHandler(comboBox1_DrawItem));
this.comboBox1.add_MeasureItem(
new MeasureItemEventHandler(comboBox1_MeasureItem));
} //InitializeComboBox
// If you set the Draw property to DrawMode.OwnerDrawVariable,
// you must handle the MeasureItem event. This event handler
// will set the height and width of each item before it is drawn.
private void comboBox1_MeasureItem(Object sender,
System.Windows.Forms.MeasureItemEventArgs e)
{
switch (e.get_Index()) {
case 0:
e.set_ItemHeight(45);
break;
case 1:
e.set_ItemHeight(20);
break;
case 2:
e.set_ItemHeight(35);
break;
}
e.set_ItemWidth(260);
} //comboBox1_MeasureItem
// You must handle the DrawItem event for owner-drawn combo boxes.
// This event handler changes the color, size and font of an
// item based on its position in the array.
private void comboBox1_DrawItem(Object sender,
System.Windows.Forms.DrawItemEventArgs e)
{
float size = 0;
System.Drawing.Font myFont;
FontFamily family = null;
System.Drawing.Color animalColor = new System.Drawing.Color();
switch (e.get_Index()) {
case 0:
size = 30;
animalColor = System.Drawing.Color.get_Gray();
family = FontFamily.get_GenericSansSerif();
break;
case 1:
size = 10;
animalColor = System.Drawing.Color.get_LawnGreen();
family = FontFamily.get_GenericMonospace();
break;
case 2:
size = 15;
animalColor = System.Drawing.Color.get_Tan();
family = FontFamily.get_GenericSansSerif();
break;
}
// Draw the background of the item.
e.DrawBackground();
// Create a square filled with the animals color. Vary the size
// of the rectangle based on the length of the animals name.
Rectangle rectangle = new Rectangle(2, e.get_Bounds().get_Top() + 2,
e.get_Bounds().get_Height(),
e.get_Bounds().get_Height() - 4);
e.get_Graphics().FillRectangle(new SolidBrush(animalColor), rectangle);
// Draw each string in the array, using a different size, color,
// and font for each item.
myFont = new Font(family, size, FontStyle.Bold);
e.get_Graphics().DrawString((String)animals.get_Item(e.get_Index()),
myFont, System.Drawing.Brushes.get_Black(),
new RectangleF(e.get_Bounds().get_X() + rectangle.get_Width(),
e.get_Bounds().get_Y(), e.get_Bounds().get_Width(),
e.get_Bounds().get_Height()));
// Draw the focus rectangle if the mouse hovers over an item.
e.DrawFocusRectangle();
} //comboBox1_DrawItem
平台
Windows 98、Windows 2000 SP4、Windows CE、Windows Millennium Edition、Windows Mobile for Pocket PC、Windows Mobile for Smartphone、Windows Server 2003、Windows XP Media Center Edition、Windows XP Professional x64 Edition、Windows XP SP2、Windows XP Starter Edition
.NET Framework 并不是对每个平台的所有版本都提供支持。有关受支持版本的列表，请参见系统要求。
版本信息
.NET Framework
受以下版本支持：2.0、1.1、1.0