如何在Asp.net中使用ComboBox？

这个没研究过，下拉用dropdownlist，之前在有一个blog里面好象看到过

完整的源碼:using System;
using System.ComponentModel;
using System.Web;
using System.Web.UI;
using System.Web.UI.HtmlControls;
using System.Web.UI.WebControls;
[assembly: TagPrefix ("Vortex.Web.UI.WebControls" , "vortex") ]
namespace Vortex.Web.UI.WebControls
{
/// <summary>
/// Represents a control that allows the user to select a single item from a drop-down list,
/// or type in a new value that is not in the list.
/// </summary>
/// <res>
/// Since the ComboBox control inherits from <see cref="System.Web.UI.WebControls.ListBox"/>,
/// you can use it in exactly the same manner (including DataBinding).
/// For older browsers that do not support the functionality required to render this control,
/// a normal dropdown box will be emitted instead.
/// </res>
[ToolboxData("<{0}:ComboBox runat=\"server\"></{0}:ComboBox>")]
[ValidationPropertyAttribute("SelectedValue")]
public class ComboBox : System.Web.UI.WebControls.ListBox
{
/// <summary>
/// The <see cref="System.Web.UI.WebControls.TextBox"/> used internally to allow the user
/// to type in new values.
/// </summary>
TextBox textBox = new TextBox(); /// <summary>
/// Indicates if the current browser supports rendering the ComboBox.
/// </summary>
bool isSupportedBrowser = false; /// <summary>
/// The maximum number of characters that a user can manually type in
/// </summary>
int maxLength = 0; /// <summary>
/// Indicates if the ComboBox control should use the AutoFill technique
/// </summary>
bool enableAutoFill = false; /// <summary>
/// The path to an external .js file that contains all of the javascript functions
/// needed by this control. If this is not set (the default behavior), then the
/// javascript is emitted inline.
/// </summary>
string externalResourcePath = null; /// <summary>
/// The ID of the containing control
/// </summary>
string masterID = "combobox"; /// <summary>
/// The client ID of the containing control
/// </summary>
string masterClientID;
/// <summary>
/// Initializes a new instance of the ComboBox control
/// </summary>
public ComboBox()
{
// determine if the current browser supports rendering the ComboBox
// (this wont work in design-time, so lets skip it)
CheckBrowserCapabilities();
}
/// <summary>
/// Initializes the ComboBox control
/// </summary>
/// <param name="e">The <see cref="EventArgs"/> passed to this method</param>
protected override void OnInit(EventArgs e)
{
base.OnInit (e); this.masterID = this.ID;
this.masterClientID = this.ClientID; // this makes the ListBox act like a DropDownList
// (we cant just use DropDownList because it does not support adding child controls)
this.SelectionMode = ListSelectionMode.Single;
this.Rows = 1; // if the current browser supports rendering of the ComboBox, we need to set up
// the internal TextBox control
if(this.isSupportedBrowser)
{
// if we are rendering a ComboBox, we change the ID of the dropdown so
// that we can give the ID to the TextBox (this is required so that the control
// works with validators)
this.ID = String.Format("{0}_dropdown", this.masterID);
this.textBox.ID = String.Format("{0}", this.masterID); this.Controls.Add(textBox);
}
} /// <summary>
/// Gets or sets the index of the selected item in the DropDownList control.
/// </summary>
/// <value>
/// The index of the selected item in the control. The default value is 0, which
/// selects the first item in the list.
/// </value>
/// <res>
/// If the current browser supports rendering this control as a ComboBox,
/// then this property will always return '-1'. Since the value can be typed
/// in, the value may not exist in the Items collection, so SelectedIndex
/// does not apply.
/// If you set the SelectedIndex property, the value will be set even if the
/// control is rendered as a ComboBox.
/// </res>
public override int SelectedIndex
{
get
{
if(this.isSupportedBrowser)
return -1;
else
return base.SelectedIndex;
}
set
{
base.SelectedIndex = value;
}
} /// <summary>
/// Gets the selected item with the lowest index in the list control.
/// </summary>
/// <res>
/// If the current browser supports rendering this control as a ComboBox,
/// then this property will always return <c>null</c>. Since the value can be typed
/// in, the value may not exist in the Items collection, so SelectedItem
/// does not apply.
/// </res>
public override ListItem SelectedItem
{
get
{
if(this.isSupportedBrowser)
{
if(base.Items.FindByText(this.textBox.Text) != null)
{
return base.Items.FindByText(this.textBox.Text);
}
else
{
return null;
}
}
else
{
return base.SelectedItem;
}
}
} /// <summary>
/// Gets the value of the selected item in the list control, or selects the item
/// in the list control that contains the specified value.
/// </summary>
public override string SelectedValue
{
get
{
if(this.isSupportedBrowser)
{
if(this.SelectedItem != null)
{
return this.SelectedItem.Value;
}
else
{
return this.textBox.Text;
}
}
else
{
return base.SelectedValue;
}
}
set
{
if(this.isSupportedBrowser)
this.textBox.Text = value;
else
{
// we need a try...catch here in case the selected value was typed
// in and thus does not exist in the Items collection
try
{
base.SelectedValue = value;
}
catch
{
// swallow the exception
}
}
}
}

/// <summary>
/// Raises the PreRender event.
/// </summary>
/// <res>
/// The common javascript functions must be dealt with here because 'RegisterClientScriptBlock'
/// cannot be called from the Render method (it is too late in the lifesycle).
/// </res>
/// <param name="e">An <see cref="EventArgs"/> object that contains the event data.</param>
protected override void OnPreRender(EventArgs e)
{
if(this.Visible && this.isSupportedBrowser)
{
// if the javascript is in an external file, render a link to it.
// otherwise, emit the javascript inline.
if(this.externalResourcePath != null)
{
this.Page.RegisterClientScriptBlock("combobox_external_functions", String.Format("<script language='javascript' type='text/javascript' src='{0}'></script>", this.ResolveUrl(this.externalResourcePath)));
}
else
{
// however, if another control has already linked in the external file, we
// cant emit the inline javascript because it will conflict. if that is the case,
// we dont have to do anything because it is already all handled.
if(!this.Page.IsClientScriptBlockRegistered("combobox_external_functions"))
{
// register the common javascript needed by all instances of the ComboBox control
this.Page.RegisterClientScriptBlock("combobox_basic_functions", javascriptBasicFunctions); // if autofill is on, emit the necessary javascript
// (we dont emit it if we dont need it to save on bandwidth)
if(this.enableAutoFill)
{
this.Page.RegisterClientScriptBlock("combobox_autofill_functions", javascriptAutoFillFunctions);
}
}
}
}
else
{
base.OnPreRender(e);
}
}
/// <summary>
/// Renders the control as HTML.
/// </summary>
/// <res>
/// If the current browser does not support the functionality required to render the
/// ComboBox, a normal <see cref="ListBox"/> will be rendered instead.
/// </res>
/// <param name="writer">The <see cref="HtmlTextWriter"/> to which to emit the resulting HTML.</param>
protected override void Render(HtmlTextWriter writer)
{
if(this.Visible && this.isSupportedBrowser)
{
// to make the control look correct, we have to pass all of the dropdown's
// visual properties to the textbox as well.
this.textBox.BackColor = this.BackColor;
this.textBox.BorderColor = this.BorderColor;
this.textBox.BorderStyle = this.BorderStyle;
this.textBox.BorderWidth = this.BorderWidth;
this.textBox.CssClass = this.CssClass;
this.textBox.Enabled = this.Enabled;
this.textBox.Font.Bold = this.Font.Bold;
this.textBox.Font.Italic = this.Font.Italic;
this.textBox.Font.Name = this.Font.Name;
this.textBox.Font.Names = this.Font.Names;
this.textBox.Font.Overline = this.Font.Overline;
this.textBox.Font.Size = this.Font.Size;
this.textBox.Font.Strikeout = this.Font.Strikeout;
this.textBox.Font.Underline = this.Font.Underline;
this.textBox.ForeColor = this.ForeColor;
this.textBox.Height = this.Height;
this.textBox.TabIndex = this.TabIndex;
this.textBox.Width = this.Width; // handle the default value
if(this.SelectedItem != null)
this.textBox.Text = this.SelectedItem.Text; // handle the maximum length
this.textBox.MaxLength = this.maxLength; // dont allow the dropdown box to get the focus if this is a ComboBox
this.TabIndex = -1; // register the javascript specific to this instance of the ComboBox
this.Page.RegisterStartupScript(this.masterClientID, String.Format(initializationScriptFormat, this.masterClientID)); // hook up the javascript 'onchange' event of the dropdown.
string onChangeCommand = String.Format("combobox_dropdown_onchange('{0}');", this.masterClientID);
this.Attributes.Add("onchange", onChangeCommand); // hook up the javascript 'onkeyup' event of the textbox, if we are using autofill
if(this.enableAutoFill)
{
this.textBox.Attributes.Add("onkeyup", String.Format("return combobox_textbox_autofill_onkeyup('{0}', event);", this.masterClientID));
} // hook up the javascript 'onkeydown' event of the text box. this makes sure the
// selectedIndex gets removed properly if a new value is typed in
this.textBox.Attributes.Add("onkeydown", String.Format("return combobox_textbox_onkeydown('{0}', event);", this.masterClientID)); // this is mainly used with 'GridLayout' where the designer has already set some
// styles that position this element
string existingStyle = this.Attributes["style"]; // these 'style' attributes are responsible (with some of the javascript initialization)
// for making sure the control renders properly
this.Attributes.Add("style", String.Format("position:absolute;top:0px;left:0px;visibility:hidden;{0}", (!this.Width.IsEmpty ? String.Format("width:{0};", this.Width.ToString()) : "")));
this.textBox.Attributes.Add("style", String.Format("top:0px;left:0px;z-index:200;{0}", (!this.Width.IsEmpty ? String.Format("width:{0};", this.Width.ToString()) : ""))); // render the control
writer.Write(String.Format("<table cellpadding=\"0\" cellspacing=\"0\" border=\"0\" id=\"{2}_container\" name=\"{2}_container\" style=\"margin:0px;padding:0px;display:inline;vertical-align:-4px;{0}{1}\"><tr><td><div style=\"position:relative;\">", (!this.Width.IsEmpty ? String.Format("width:{0};", this.Width.ToString()) : ""), existingStyle, this.masterClientID));
base.Render(writer);
this.textBox.RenderControl(writer);
writer.Write("</div></td></tr></table>");
}
else
{
// if the ComboBox is not supported by the current browser, just render
// a plain old ListBox. we also do this if the control is in design-mode
base.Render(writer);
}
} /// <summary>
/// Checks the current browser to determine if it supports the functionality required
/// to render the ComboBox.
/// </summary>
/// <res>
/// This is currently coded to emit the ComboBox in IE 5+, Netscape 6+, Mozilla 1+,
/// and Firefox 1+. These were the only browsers that I could accurately verify that
/// the ComboBox rendered correctly in.
/// All other browsers will get a standard <see cref="ListBox"/> control.
/// If you can verify that other browsers support the rendering requirements (like Opera,
/// etc), then you can modify this method OR your browser capabilities section in the
/// machine.config.
/// </res>
private void CheckBrowserCapabilities()
{
bool result = false;
if(HttpContext.Current != null)
{
if(HttpContext.Current.Request.Browser.JavaScript)
{
// allow IE 5+
if(HttpContext.Current.Request.Browser.W3CDomVersion.Major >= 1)
{
result = true;
}
else
{
// allow NS 5+, MZ 1+, and FireFox 1+
if(HttpContext.Current.Request.Browser.Browser == "Netscape" && HttpContext.Current.Request.Browser.MajorVersion >= 5)
{
result = true;
}
}
}
}
this.isSupportedBrowser = result;
}

/// <summary>
/// Indicates if the current browser supports rendering the control as a ComboBox or not
/// </summary>
/// <value>
/// <c>true</c> if the browser supports rendering the ComboBox control;
/// <c>false</c> if the browser is incapable of rendering the ComboBox control.
/// </value>
/// <res>
/// If the current browser does NOT support rendering the ComboBox control, a simple
/// <see cref="ListBox"/> control will be rendered instead.
/// </res>
[Description("Indicates if the current browser supports rendering the control as a ComboBox or not." ),
Browsable (true) ,
Category("Behavior")]
public bool IsSupportedBrowser
{
get
{
return this.isSupportedBrowser;
}
set
{
this.isSupportedBrowser = value;
}
} /// <summary>
/// Indicates if the ComboBox should use the AutoFill technique
/// </summary>
/// <value>
/// <c>true</c> if the control should AutoFill;
/// <c>false</c> otherwise [default].
/// </value>
/// <res>
/// If the current browser does NOT support rendering the ComboBox control, this
/// property has no effect.
/// </res>
[Description("Indicates if the ComboBox should use the AutoFill technique." ),
Browsable (true) ,
Category("Behavior")]
public bool EnableAutoFill
{
get
{
return this.enableAutoFill;
}
set
{
this.enableAutoFill = value;
}
} /// <summary>
/// Gets or sets the maximum number of characters allowed to be manually entered.
/// </summary>
/// <value>
/// The maxumum number of characters allowed to be manually entered.
/// The default is 0, which indicates that the property is not set.
/// </value>
/// <res>
/// If the current browser does not support rendering of the ComboBox, this
/// property has no effect.
/// </res>
[Description("Gets or sets the maximum number of characters allowed to be manually entered." ),
Browsable (true) ,
Category("Behavior")]
public int MaxLength
{
get
{
return this.maxLength;
}
set
{
this.maxLength = value;
}
} /// <summary>
/// Sets the path to an external .js file that contains all of the javascript
/// required by this control. If not set, the javascript will be emitted inline.
/// </summary>
/// <value>
/// The valid path to the .js file, or <c>null</c>.
/// </value>
/// <res>
/// If the current browser does not support rendering of the ComboBox, this
/// property has no effect.
/// </res>
[Description("Sets the path to an external .js file that contains all of the javascript required by this control. If not set, the javascript will be emitted inline." ),
Browsable (true) ,
Category("Behavior")]
public string ExternalResourcePath
{
get
{
return this.externalResourcePath;
}
set
{
this.externalResourcePath = value;
}
} /// <summary>
/// The format of the javascript that will be emitted for each ComboBox control that
/// is placed on the page.
/// </summary>
private static string initializationScriptFormat = "<script type='text/javascript'>combobox_initialize('{0}');</script>"; /// <summary>
/// The basic javascript that needs to be emitted once per page that contains any ComboBox
/// controls.
/// (This would be nice if it were not in the compiled code so that it could be edited/
/// updated with out a recompile. However, in the interest of making this control self-
/// contained and simple for the demo, it is just included here. It could easily be moved
/// to a seperate .js file that is referenced here.)
/// </summary>
private static string javascriptBasicFunctions = @"
<script type='text/javascript'>

</script>
";

再加上 /// <summary>
/// The auto-fill javascript that needs to be emitted once per page that contains any ComboBox
/// controls.
/// (This would be nice if it were not in the compiled code so that it could be edited/
/// updated with out a recompile. However, in the interest of making this control self-
/// contained and simple for the demo, it is just included here. It could easily be moved
/// to a seperate .js file that is referenced here.)
/// </summary>
private static string javascriptAutoFillFunctions = @"
<script type='text/javascript'>

</script>
";
}
}

实用是很简单的..comboBox.是可以实现手动输入可下拉选择....不清楚楼主想那里不会??
要是想学习这个控件的使用方法:C#自己带的SDK里面有这个控件的详细使用说明..

调试易

如何在Asp.net中使用ComboBox？

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