ASP.NET 页框架提供一种称为“事件冒泡”的技术，允许子控件将事件沿其包容层次结构向上传播。事件冒泡允许在控件层次结构中更方便的位置引发事件，并且允许将事件处理程序附加到原始控件以及公开冒泡的事件的控件上。
数据绑定控件（Repeater、DataList 和 DataGrid）使用事件冒泡将子控件（在项目模板内）引发的命令事件公开为顶级事件。虽然 .NET Framework 中的 ASP.NET 服务器控件将事件冒泡用于命令事件（事件数据类是从 CommandEventArgs 派生的事件），但是，服务器控件上定义的任何事件都可以冒泡。
控件可以通过从基类 System.Web.UI.Control 继承的两个方法参与事件冒泡。这两个方法是：OnBubbleEvent 和 RaiseBubbleEvent。以下代码片段显示了这些方法的签名。
[C#]protected virtual bool OnBubbleEvent( object source, EventArgs args);protected void RaiseBubbleEvent( object source, EventArgs args );[Visual Basic]Overridable Protected Function OnBubbleEvent( _ ByVal source As Object, _ ByVal args As EventArgs _) As BooleanProtected Sub RaiseBubbleEvent( _ ByVal source As Object, _ ByVal args As EventArgs _)RaiseBubbleEvent 的实现是由 Control 提供的，并且不能被重写。RaiseBubbleEvent 沿层次结构向上将事件数据发送到控件的父级。若要处理或引发冒泡的事件，控件必须重写 OnBubbleEvent 方法。
使事件冒泡的控件执行以下三种操作之一。
控件不执行任何操作，此时事件自动向上冒泡到其父级。 控件进行一些处理并继续使事件冒泡。若要实现这一点，控件必须重写 OnBubbleEvent，并从 OnBubbleEvent 调用 RaiseBubbleEvent。以下代码片段（摘自模板化数据绑定控件示例）在检查事件参数的类型后使事件冒泡。 [C#]protected override bool OnBubbleEvent(object source, EventArgs e) { if (e is CommandEventArgs) { // Adds information about an Item to the // CommandEvent. TemplatedListCommandEventArgs args = new TemplatedListCommandEventArgs(this, source, (CommandEventArgs)e); RaiseBubbleEvent(this, args); return true; } return false; }[Visual Basic]Protected Overrides Function OnBubbleEvent(source As Object, e As EventArgs) As Boolean If TypeOf e Is CommandEventArgs Then ' Adds information about an Item to the ' CommandEvent. Dim args As New TemplatedListCommandEventArgs(Me, source, CType(e, CommandEventArgs)) RaiseBubbleEvent(Me, args) Return True End If Return FalseEnd Function控件停止事件冒泡并引发和/或处理该事件。引发事件需要调用将事件调度给侦听器的方法。若要引发冒泡的事件，控件必须重写 OnBubbleEvent 以调用引发此冒泡的事件的 OnEventName 方法。引发冒泡的事件的控件通常将冒泡的事件公开为顶级事件。以下代码片段（摘自模板化数据绑定控件示例）引发一个冒泡的事件。 [C#]protected override bool OnBubbleEvent(object source, EventArgs e) { bool handled = false;
if (e is TemplatedListCommandEventArgs) { TemplatedListCommandEventArgs ce = (TemplatedListCommandEventArgs)e;
OnItemCommand(ce); handled = true; } return handled;}[Visual Basic]Protected Overrides Function OnBubbleEvent(source As Object, e As EventArgs) As Boolean Dim handled As Boolean = False If TypeOf e Is TemplatedListCommandEventArgs Then Dim ce As TemplatedListCommandEventArgs = CType(e, TemplatedListCommandEventArgs) OnItemCommand(ce) handled = True End If Return handledEnd Function有关说明事件冒泡的示例，请参见事件冒泡控件示例和模板化数据绑定控件示例。
注意 虽然启用事件冒泡的方法 OnBubbleEvent 符合用于引发事件的方法的标准 .NET Framework 命名模式，但是没有名为 BubbleEvent 的事件。在停止事件冒泡的控件中，将冒泡事件公开为顶级事件。例如，DataList 控件将其模板中控件的 Command 事件公开为 ItemCommand 事件。另请注意，在 .NET Framework 中 OnEventName 方法的标准签名有一个参数 (protected void OnEventName (EventArgs e))。但是，OnBubbleEvent 有两个参数，这是因为该事件起源于控件之外；第二个参数提供源。到目前为止，本讨论说明了控件如何响应冒泡的事件。下面一节显示如何创作一个定义冒泡的事件的控件。
定义冒泡的事件如果希望控件为它所定义的事件启用事件冒泡，则控件必须从引发该事件的 OnEventName 方法调用 RaiseBubbleEvent。不需要在该控件中做额外的工作。以下代码片段显示了一个控件，该控件定义了一个启用冒泡的 Command 事件。
[C#]protected virtual void OnCommand(CommandEventArgs e) { CommandEventHandler handler = (CommandEventHandler)Events[EventCommand]; if (handler != null) handler(this,e);
// The Command event is bubbled up the control hierarchy. RaiseBubbleEvent(this, e); } [Visual Basic]Protected Overridable Sub OnCommand(e As CommandEventArgs) Dim handler As CommandEventHandler = CType(Events(EventCommand), CommandEventHandler) If Not (handler Is Nothing) Then handler(Me, e) End If ' The Command event is bubbled up the control hierarchy. RaiseBubbleEvent(Me, e)End Sub注意 事件冒泡并不限于命令事件。可以使用此处描述的机制使任何事件冒泡。请参见事件冒泡控件示例 | 模板化数据绑定控件示例
事件冒泡控件示例下面的自定义控件 EventBubbler 说明了一种简单的事件冒泡情况。EventBubbler 是一个包含文本框 (TextBox)、按钮 (Button) 和标签 (Label) 控件的复合控件。EventBubbler 将命令事件从按钮冒泡到父容器控件（自身），并将它们公开为顶级事件。若要生成该示例，请参见服务器控件示例中的说明。
有关更切合实际的示例，请参见模板化数据绑定控件示例。
[C#]using System;using System.Web;using System.Web.UI;using System.Web.UI.WebControls;
namespace CustomControls { public class EventBubbler : Control, INamingContainer { private int number = 100; private Label label; private TextBox box1; private TextBox box2; public event EventHandler Click; public event EventHandler Reset; public event EventHandler Submit; public string Label { get { EnsureChildControls(); return label.Text; } set { EnsureChildControls(); label.Text = value; } } public int Number { get { return number; } set { number = value; } } public string Text1 { get { EnsureChildControls(); return box1.Text; } set { EnsureChildControls(); box1.Text = value; } } public string Text2 { get { EnsureChildControls(); return box2.Text; } set { EnsureChildControls(); box2.Text = value; } } protected override void CreateChildControls() { Controls.Add(new LiteralControl("<h3>Enter a number : ")); box1 = new TextBox(); box1.Text = "0"; Controls.Add(box1); Controls.Add(new LiteralControl("</h3>")); Controls.Add(new LiteralControl("<h3>Enter another number : ")); box2 = new TextBox(); box2.Text = "0"; Controls.Add(box2); Controls.Add(new LiteralControl("</h3>")); Button button1 = new Button(); button1.Text = "Click"; button1.CommandName = "Click"; Controls.Add(button1); Button button2 = new Button(); button2.Text = "Reset"; button2.CommandName = "Reset"; Controls.Add(button2); Button button3 = new Button(); button3.Text = "Submit"; button3.CommandName = "Submit"; Controls.Add(button3); Controls.Add(new LiteralControl("<br><br>")); label = new Label(); label.Height = 50; label.Width = 500; label.Text = "Click a button."; Controls.Add(label); } protected override bool OnBubbleEvent(object source, EventArgs e) { bool handled = false; if (e is CommandEventArgs) { CommandEventArgs ce = (CommandEventArgs)e; if (ce.CommandName == "Click") { OnClick(ce); handled = true; } else if (ce.CommandName == "Reset") { OnReset(ce); handled = true; } else if (ce.CommandName == "Submit") { OnSubmit(ce); handled = true; } } return handled; } protected virtual void OnClick (EventArgs e) { if (Click != null) { Click(this,e); } } protected virtual void OnReset (EventArgs e) { if (Reset != null) { Reset(this,e); } } protected virtual void OnSubmit (EventArgs e) { if (Submit != null) { Submit(this,e); } } }}[Visual Basic]Option ExplicitOption Strict
Imports SystemImports System.WebImports System.Web.UIImports System.Web.UI.WebControls
Namespace CustomControls Public Class EventBubbler Inherits Control Implements INamingContainer Private _number As Integer = 100 Private _label As Label Private _box1 As TextBox Private _box2 As TextBox Public Event Click As EventHandler Public Event Reset As EventHandler Public Event Submit As EventHandler Public Property Label() As String Get EnsureChildControls() Return _label.Text End Get Set EnsureChildControls() _label.Text = value End Set End Property Public Property Number() As Integer Get Return _number End Get Set _number = value End Set End Property Public Property Text1() As String Get EnsureChildControls() Return _box1.Text End Get Set EnsureChildControls() _box1.Text = value End Set End Property Public Property Text2() As String Get EnsureChildControls() Return _box2.Text End Get Set EnsureChildControls() _box2.Text = value End Set End Property Protected Overrides Sub CreateChildControls() Controls.Add(New LiteralControl("<h3>Enter a number : ")) _box1 = New TextBox() _box1.Text = "0" Controls.Add(_box1) Controls.Add(New LiteralControl("</h3>")) Controls.Add(New LiteralControl("<h3>Enter another number : ")) _box2 = New TextBox() _box2.Text = "0" Controls.Add(_box2) Controls.Add(New LiteralControl("</h3>")) Dim button1 As New Button() button1.Text = "Click" button1.CommandName = "Click" Controls.Add(button1) Dim button2 As New Button() button2.Text = "Reset" button2.CommandName = "Reset" Controls.Add(button2) Dim button3 As New Button() button3.Text = "Submit" button3.CommandName = "Submit" Controls.Add(button3) Controls.Add(New LiteralControl("<br><br>")) _label = New Label() _label.Height = Unit.Pixel(50) _label.Width = Unit.Pixel(500) _label.Text = "Click a button." Controls.Add(_label) End Sub Protected Overrides Function OnBubbleEvent(source As Object, e As EventArgs) As Boolean Dim handled As Boolean = False If TypeOf e Is CommandEventArgs Then Dim ce As CommandEventArgs = CType(e, CommandEventArgs) If ce.CommandName = "Click" Then OnClick(ce) handled = True Else If ce.CommandName = "Reset" Then OnReset(ce) handled = True Else If ce.CommandName = "Submit" Then OnSubmit(ce) handled = True End If End If End If End If Return handled End Function Protected Overridable Sub OnClick(e As EventArgs) RaiseEvent Click(Me, e) End Sub Protected Overridable Sub OnReset(e As EventArgs) RaiseEvent Reset(Me, e) End Sub Protected Overridable Sub OnSubmit(e As EventArgs) RaiseEvent Submit(Me, e) End Sub End ClassEnd Namespace在页上使用事件冒泡控件下面的 ASP.NET 页使用自定义事件冒泡控件 EventBubbler，并将事件处理程序附加到其顶级事件。
[C#]<%@ Register TagPrefix="Custom" Namespace="CustomControls" Assembly = "CustomControls" %><html><script language="C#" runat=server>
private void ClickHandler(Object sender,EventArgs e) { MyControl.Label = "You clicked the <b> Click </b> button";
}
private void ResetHandler(Object sender,EventArgs e) { MyControl.Text1 = "0"; MyControl.Text2 = "0";
}
private void SubmitHandler(Object sender,EventArgs e) { if ( Int32.Parse(MyControl.Text1) + Int32.Parse(MyControl.Text2) == MyControl.Number) MyControl.Label = "<h2> You won a million dollars!!!! </h2>"; else MyControl.Label = "Sorry, try again. The numbers you entered don't add up to" + " the hidden number.";
} </script> <body>
<h1> The Mystery Sum Game </h1><br> <form runat=server> <Custom:EventBubbler id = "MyControl" OnClick = "ClickHandler" OnReset = "ResetHandler" OnSubmit = "SubmitHandler" Number= "10" runat = server/> </form> </body> </html> [Visual Basic]<%@ Register TagPrefix="Custom" Namespace="CustomControls" Assembly = "CustomControls" %><html><script language="VB" runat=server>
Private Sub ClickHandler(sender As Object, e As EventArgs) MyControl.Label = "You clicked the <b> Click </b> button" End Sub
Private Sub ResetHandler(sender As Object, e As EventArgs) MyControl.Text1 = "0" MyControl.Text2 = "0" End Sub
Private Sub SubmitHandler(sender As Object, e As EventArgs) If Int32.Parse(MyControl.Text1) + Int32.Parse(MyControl.Text2) = MyControl.Number Then MyControl.Label = "<h2> You won a million dollars!!!! </h2>" Else MyControl.Label = "Sorry, try again. The numbers you entered don't add up to" & " the hidden number." End If End Sub </script> <body>
<h1> The Mystery Sum Game </h1><br> <form runat=server> <Custom:EventBubbler id = "MyControl" OnClick = "ClickHandler" OnReset = "ResetHandler" OnSubmit = "SubmitHandler" Number= "10" runat = server/> </form> </body> </html>
