ASP.NET AJAX Advance Tips & Tricks (1) CascadingDropDown在IE和Safari中的一个缺陷和解决方法
前言:
ASP.NET AJAX Toolkit中的CascadingDropDown简单易用,但在IE和Safari中有一个比较明显的性能缺陷,当数据量大,并且用户使用鼠标滚轮或键盘上下键选取选项时,这个缺陷非常明显。本文介绍通过修改Toolkit源代码来解决这个问题。(这个问题应该会比较争议,也许很多人并不将其视为缺陷,视情况而定吧)
问题重现:
大家可以到ASP.NET AJAX Toolkit官方展示页面看看:http://www.asp.net/AJAX/AjaxControlToolkit/Samples/CascadingDropDown/CascadingDropDown.aspx
如下图所示,当鼠标焦点在父级列表框上时,如果你用的是IE或Safari,请尝试着用鼠标滚轮,或键盘上下键来更换选项,这时就会发现每次父列表框选项的更改都使子列表框中的选项更新。这意味着,每次更改都发送了一个WebService请求,去获取子列表框中的列表项集合!
然而在Firefox下,我们会发现,当我们尝试用鼠标滚轮,或键盘上下键来更换选项时,子列表框中的选项并没有更新,直至父列表框失去焦点。
可以想象一下,如果子列表选项集合比较庞大,CascadingDropDown在IE或Safari下的表现将会是一个非常大的性能损耗。
原因:
我认为这个现象是由于<select>的onchange事件在IE或Safari和Firefox下的不同执行方式而引起的。
我们可以分别在FF和IE下试验以下代码,将会发现与上面类似的问题
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<title>Untitled Page</title>
<style type="text/css">
#Select1
{
height: 19px;
width: 155px;
}
</style>
<script type="text/javascript">
function call()
{
window.alert("change");
}
</script>
</head>
<body>
<select id="Select1" name="D1" onchange="call();">
<option>aaaa</option>
<option>bbbb</option>
<option>cccc</option>
<option>dddd</option>
<option>eeee</option>
</select>
</body>
</html>
解决方案:
找到AjaxControlToolkit项目下的CascadingDropDownBehavior.js文件,将其中关于注册onchange事件的代码修改成onblur,如下所示,重新编译,即可在IE中实现在FF中的效果:
![](https://www.cnblogs.com/Images/OutliningIndicators/ContractedBlock.gif)
![](https://www.cnblogs.com/Images/OutliningIndicators/ExpandedBlockStart.gif)
// (c) Copyright Microsoft Corporation.
// This source is subject to the Microsoft Permissive License.
// See http://www.microsoft.com/resources/sharedsource/licensingbasics/sharedsourcelicenses.mspx.
// All other rights reserved.
/// <reference name="MicrosoftAjax.debug.js" />
/// <reference name="MicrosoftAjaxTimer.debug.js" />
/// <reference name="MicrosoftAjaxWebForms.debug.js" />
/// <reference path="../ExtenderBase/BaseScripts.js" />
/// <reference path="../Common/Common.js" />
Type.registerNamespace('AjaxControlToolkit');
AjaxControlToolkit.CascadingDropDownSelectionChangedEventArgs = function(oldValue, newValue) {
/// <summary>
/// Event arguments used when the selectionChanged event is raised
/// </summary>
/// <param name="oldValue" type="String" mayBeNull="true">
/// Previous selection
/// </param>
/// <param name="newValue" type="String" mayBeNull="true">
/// New selection
/// </param>
AjaxControlToolkit.CascadingDropDownSelectionChangedEventArgs.initializeBase(this);
this._oldValue = oldValue;
this._newValue = newValue;
}
AjaxControlToolkit.CascadingDropDownSelectionChangedEventArgs.prototype = {
get_oldValue : function() {
/// <value type="String" mayBeNull="true">
/// Previous selection
/// </value>
return this._oldValue;
},
get_newValue : function() {
/// <value type="String" mayBeNull="true">
/// New selection
/// </value>
return this._newValue;
}
}
AjaxControlToolkit.CascadingDropDownSelectionChangedEventArgs.registerClass('AjaxControlToolkit.CascadingDropDownSelectionChangedEventArgs', Sys.EventArgs);
AjaxControlToolkit.CascadingDropDownBehavior = function(e) {
/// <summary>
/// The CascadingDropDownBehavior is used to populate drop downs with values from a web service
/// </summary>
/// <param name="e" type="Sys.UI.DomElement" domElement="true">
/// The DOM element the behavior is associated with
/// </param>
AjaxControlToolkit.CascadingDropDownBehavior.initializeBase(this, [e]);
// Properties
this._parentControlID = null;
this._category = null;
this._promptText = null;
this._loadingText = null;
this._promptValue = null;
this._emptyValue = null;
this._emptyText = null;
// Path to the web service, or null if a page method
this._servicePath = null;
// Name of the web method
this._serviceMethod = null;
// User/page specific context provided to the web method
this._contextKey = null;
// Whether or not the the user/page specific context should be used
this._useContextKey = false;
// Variables
this._parentElement = null;
this._changeHandler = null;
this._parentChangeHandler = null;
this._lastParentValues = null;
this._selectedValue = null;
}
AjaxControlToolkit.CascadingDropDownBehavior.prototype = {
initialize : function() {
/// <summary>
/// Initialize the behavior
/// </summary>
/// <returns />
AjaxControlToolkit.CascadingDropDownBehavior.callBaseMethod(this, 'initialize');
$common.prepareHiddenElementForATDeviceUpdate();
var e = this.get_element();
// Clear any items that may have been put there for server side convenience
this._clearItems();
e.CascadingDropDownCategory = this._category;
// Attach change handler to self
this._changeHandler = Function.createDelegate(this, this._onChange);
$addHandler(e, "blur",this._changeHandler);
if (this._parentControlID) {
// Set properties on element so that children controls (if any) can have easy access
this._parentElement = $get(this._parentControlID);
// Attach change handler to parent
Sys.Debug.assert(this._parentElement != null, String.format(AjaxControlToolkit.Resources.CascadingDropDown_NoParentElement, this._parentControlID));
if (this._parentElement) {
e.CascadingDropDownParentControlID = this._parentControlID;
this._parentChangeHandler = Function.createDelegate(this, this._onParentChange);
$addHandler(this._parentElement, "blur", this._parentChangeHandler);
if (!this._parentElement.childDropDown) {
this._parentElement.childDropDown = new Array();
}
this._parentElement.childDropDown.push(this);
}
}
// Simulate parent change to populate self, even if no parent exists.
this._onParentChange(null, true);
},
dispose : function() {
/// <summary>
/// Dispose the behavior
/// </summary>
/// <returns />
var e = this.get_element();
// Detach change handler for self
if (this._changeHandler) {
$removeHandler(e, "blur", this._changeHandler);
this._changeHandler = null;
}
// Detach change handler for parent
if (this._parentChangeHandler) {
if (this._parentElement) {
$removeHandler(this._parentElement, "blur", this._parentChangeHandler);
}
this._parentChangeHandler = null;
}
AjaxControlToolkit.CascadingDropDownBehavior.callBaseMethod(this, 'dispose');
},
_clearItems : function() {
/// <summary>
/// Clear the items from the drop down
/// </summary>
/// <returns />
var e = this.get_element();
while (0 < e.options.length) {
e.remove(0);
}
},
_isPopulated : function() {
/// <summary>
/// Determine whether the drop down has any items
/// </summary>
/// <returns type="Boolean">
/// Whether the drop down has any items
/// </returns>
var items = this.get_element().options.length;
if (this._promptText) {
return items > 1;
} else {
return items > 0;
}
},
_setOptions : function(list, inInit, gettingList) {
/// <summary>
/// Set the contents of the DropDownList to the specified list
/// </summary>
/// <param name="list" mayBeNull="true" elementType="Object">
/// Array of options (where each option has name and value properties)
/// </param>
/// <param name="inInit" type="Boolean" optional="true">
/// Whether this is being called from the initialize method
/// </param>
/// <param name="gettingList" type="Boolean" optional="true">
/// Whether we are fetching the list of options from the web service
/// </param>
/// <returns />
if (!this.get_isInitialized()) {
return;
}
var e = this.get_element();
// Remove existing contents
this._clearItems();
// Populate prompt text (if available)
var headerText;
var headerValue = "";
if (gettingList && this._loadingText) {
headerText = this._loadingText;
} else if (!gettingList && list && (0 == list.length) && (null != this._emptyText)) {
headerText = this._emptyText;
if (this._emptyValue) {
headerValue = this._emptyValue;
}
} else if (this._promptText) {
headerText = this._promptText;
if (this._promptValue) {
headerValue = this._promptValue;
}
}
if (headerText) {
var optionElement = new Option(headerText, headerValue);
e.options[e.options.length] = optionElement;
}
// Add each item to the DropDownList, selecting the previously selected item
var selectedValueOption = null;
var defaultIndex = -1;
if (list) {
for (i = 0 ; i < list.length ; i++) {
var listItemName = list[i].name;
var listItemValue = list[i].value;
if (list[i].isDefaultValue) {
defaultIndex = i;
if (this._promptText) {
// bump the index if there's a prompt item in the list.
//
defaultIndex++;
}
}
var optionElement = new Option(listItemName, listItemValue);
if (listItemValue == this._selectedValue) {
selectedValueOption = optionElement;
}
e.options[e.options.length] = optionElement;
}
if (selectedValueOption) {
selectedValueOption.selected = true;
}
}
// if we didn't match the selected value, and we found a default
// item, select that one.
//
if (selectedValueOption) {
// Call set_SelectedValue to store the text as well
this.set_SelectedValue(e.options[e.selectedIndex].value, e.options[e.selectedIndex].text);
} else if (!selectedValueOption && defaultIndex != -1) {
e.options[defaultIndex].selected = true;
this.set_SelectedValue(e.options[defaultIndex].value, e.options[defaultIndex].text);
} else if (!inInit && !selectedValueOption && !gettingList && !this._promptText && (e.options.length > 0)) {
// If no prompt text or default item, select the first item
this.set_SelectedValue(e.options[0].value, e.options[0].text);
} else if (!inInit && !selectedValueOption && !gettingList) {
this.set_SelectedValue('', '');
}
if (e.childDropDown && !gettingList) {
for(i = 0; i < e.childDropDown.length; i++) {
e.childDropDown[i]._onParentChange();
}
}
else {
if (list && (Sys.Browser.agent !== Sys.Browser.Safari) && (Sys.Browser.agent !== Sys.Browser.Opera)) {
// Fire the onchange event for the control to notify any listeners of the change
if (document.createEvent) {
var onchangeEvent = document.createEvent('HTMLEvents');
onchangeEvent.initEvent('blur', true, false);
this.get_element().dispatchEvent(onchangeEvent);
} else if( document.createEventObject ) {
this.get_element().fireEvent('onblur');
}
}
}
// Disable the control if loading/prompt text is present and an empty list was populated
if (this._loadingText || this._promptText || this._emptyText) {
e.disabled = !list || (0 == list.length);
}
this.raisePopulated(Sys.EventArgs.Empty);
},
_onChange : function() {
/// <summary>
/// Handler for the drop down's change event
/// </summary>
/// <returns />
if (!this._isPopulated()) {
return;
}
var e = this.get_element();
// Record the selected value in the client state
if ((-1 != e.selectedIndex) && !(this._promptText && (0 == e.selectedIndex))) {
this.set_SelectedValue(e.options[e.selectedIndex].value, e.options[e.selectedIndex].text);
} else {
this.set_SelectedValue('', '');
}
},
_onParentChange : function(evt, inInit) {
/// <summary>
/// Handler for the parent drop down's change event
/// </summary>
/// <param name="evt" type="Object">
/// Set by the browser when called as an event handler (unused here)
/// </param>
/// <param name="inInit" type="Boolean">
/// Whether this is being called from the initialize method
/// </param>
/// <returns />
var e = this.get_element();
// Create the known category/value pairs string for sending to the helper web service
// Follow parent pointers so that the complete state can be sent
// Format: 'name1:value1;name2:value2;
![](https://www.cnblogs.com/Images/dot.gif)
var knownCategoryValues = '';
var parentControlID = this._parentControlID;
while (parentControlID) {
var parentElement = $get(parentControlID);
if (parentElement && (-1 != parentElement.selectedIndex)){
var selectedValue = parentElement.options[parentElement.selectedIndex].value;
if (selectedValue && selectedValue != "") {
knownCategoryValues = parentElement.CascadingDropDownCategory + ':' + selectedValue + ';' + knownCategoryValues;
parentControlID = parentElement.CascadingDropDownParentControlID;
continue;
}
}
break;
}
if (knownCategoryValues != '' && this._lastParentValues == knownCategoryValues) {
return;
}
this._lastParentValues = knownCategoryValues;
// we have a parent but it doesn't have a valid value
//
if (knownCategoryValues == '' && this._parentControlID) {
this._setOptions(null, inInit);
return;
}
// Show the loading text (if any)
this._setOptions(null, inInit, true);
if (this._servicePath && this._serviceMethod) {
// Raise the populating event and optionally cancel the web service invocation
var eventArgs = new Sys.CancelEventArgs();
this.raisePopulating(eventArgs);
if (eventArgs.get_cancel()) {
return;
}
// Create the service parameters and optionally add the context parameter
// (thereby determining which method signature we're expecting
![](https://www.cnblogs.com/Images/dot.gif)
var params = { knownCategoryValues:knownCategoryValues, category:this._category };
if (this._useContextKey) {
params.contextKey = this._contextKey;
}
// Call the helper web service
Sys.Net.WebServiceProxy.invoke(this._servicePath, this._serviceMethod, false, params,
Function.createDelegate(this, this._onMethodComplete), Function.createDelegate(this, this._onMethodError));
$common.updateFormToRefreshATDeviceBuffer();
}
},
_onMethodComplete : function(result, userContext, methodName) {
// Success, update the DropDownList
this._setOptions(result);
},
_onMethodError : function(webServiceError, userContext, methodName) {
// Indicate failure
if (webServiceError.get_timedOut()) {
this._setOptions( [ this._makeNameValueObject(AjaxControlToolkit.Resources.CascadingDropDown_MethodTimeout) ] );
} else {
this._setOptions( [ this._makeNameValueObject(String.format(AjaxControlToolkit.Resources.CascadingDropDown_MethodError, webServiceError.get_statusCode())) ] );
}
},
_makeNameValueObject : function(message) {
/// <summary>
/// Create an object with name and value properties set to the provided message
/// </summary>
/// <param name="message" type="String">
/// Message
/// </param>
/// <returns type="Object">
/// Object with name and value properties set to the message
/// </returns>
return { 'name': message, 'value': message };
},
get_ParentControlID : function() {
/// <value type="String">
/// ID of the parent drop down in a hierarchy of drop downs
/// </value>
return this._parentControlID;
},
set_ParentControlID : function(value) {
if (this._parentControlID != value) {
this._parentControlID = value;
this.raisePropertyChanged('ParentControlID');
}
},
get_Category : function() {
/// <value type="String">
/// Category of this drop down
/// </value>
return this._category;
},
set_Category : function(value) {
if (this._category != value) {
this._category = value;
this.raisePropertyChanged('Category');
}
},
get_PromptText : function() {
/// <value type="String">
/// Prompt text displayed as the first entry in the drop down
/// </value>
return this._promptText;
},
set_PromptText : function(value) {
if (this._promptText != value) {
this._promptText = value;
this.raisePropertyChanged('PromptText');
}
},
get_PromptValue : function() {
/// <value type="String">
/// Value for the option displayed by a DropDownList showing the PromptText
/// </value>
return this._promptValue;
},
set_PromptValue : function(value) {
if (this._promptValue != value) {
this._promptValue = value;
this.raisePropertyChanged('PromptValue');
}
},
get_EmptyText : function() {
/// <value type="String">
/// Text for the option displayed when the list is empty
/// </value>
return this._emptyText;
},
set_EmptyText : function(value) {
if (this._emptyText != value) {
this._emptyText = value;
this.raisePropertyChanged('EmptyText');
}
},
get_EmptyValue : function() {
/// <value type="String">
/// Value for the option displayed when the list is empty
/// </value>
return this._emptyValue;
},
set_EmptyValue : function(value) {
if (this._emptyValue != value) {
this._emptyValue = value;
this.raisePropertyChanged('EmptyValue');
}
},
get_LoadingText : function() {
/// <value type="String">
/// Loading text to to be displayed when getting the drop down's values from the web service
/// </value>
return this._loadingText;
},
set_LoadingText : function(value) {
if (this._loadingText != value) {
this._loadingText = value;
this.raisePropertyChanged('LoadingText');
}
},
get_SelectedValue : function() {
/// <value type="String">
/// Selected value of the drop down
/// </value>
return this._selectedValue;
},
set_SelectedValue : function(value, text) {
if (this._selectedValue != value) {
if (!text) {
// Initial population by server; look for "value:::text" pair
var i = value.indexOf(':::');
if (-1 != i) {
text = value.slice(i + 3);
value = value.slice(0, i);
}
}
var oldValue = this._selectedValue;
this._selectedValue = value;
this.raisePropertyChanged('SelectedValue');
this.raiseSelectionChanged(new AjaxControlToolkit.CascadingDropDownSelectionChangedEventArgs(oldValue, value));
}
AjaxControlToolkit.CascadingDropDownBehavior.callBaseMethod(this, 'set_ClientState', [ this._selectedValue+':::'+text ]);
},
get_ServicePath : function() {
/// <value type="String" mayBeNull="true">
/// Path to the web service
/// </value>
return this._servicePath;
},
set_ServicePath : function(value) {
if (this._servicePath != value) {
this._servicePath = value;
this.raisePropertyChanged('ServicePath');
}
},
get_ServiceMethod : function() {
/// <value type="String">
/// Name of the method to invoke on the web service
/// </value>
return this._serviceMethod;
},
set_ServiceMethod : function(value) {
if (this._serviceMethod != value) {
this._serviceMethod = value;
this.raisePropertyChanged('ServiceMethod');
}
},
get_contextKey : function() {
/// <value type="String" mayBeNull="true">
/// User/page specific context provided to an optional overload of the
/// web method described by ServiceMethod/ServicePath. If the context
/// key is used, it should have the same signature with an additional
/// parameter named contextKey of type string.
/// </value>
return this._contextKey;
},
set_contextKey : function(value) {
if (this._contextKey != value) {
this._contextKey = value;
this.set_useContextKey(true);
this.raisePropertyChanged('contextKey');
}
},
get_useContextKey : function() {
/// <value type="Boolean">
/// Whether or not the ContextKey property should be used. This will be
/// automatically enabled if the ContextKey property is ever set
/// (on either the client or the server). If the context key is used,
/// it should have the same signature with an additional parameter
/// named contextKey of type string.
/// </value>
return this._useContextKey;
},
set_useContextKey : function(value) {
if (this._useContextKey != value) {
this._useContextKey = value;
this.raisePropertyChanged('useContextKey');
}
},
add_selectionChanged : function(handler) {
/// <summary>
/// Add an event handler for the selectionChanged event
/// </summary>
/// <param name="handler" type="Function" mayBeNull="false">
/// Event handler
/// </param>
/// <returns />
this.get_events().addHandler('selectionChanged', handler);
},
remove_selectionChanged : function(handler) {
/// <summary>
/// Remove an event handler from the selectionChanged event
/// </summary>
/// <param name="handler" type="Function" mayBeNull="false">
/// Event handler
/// </param>
/// <returns />
this.get_events().removeHandler('selectionChanged', handler);
},
raiseSelectionChanged : function(eventArgs) {
/// <summary>
/// Raise the selectionChanged event
/// </summary>
/// <param name="eventArgs" type="AjaxControlToolkit.CascadingDropDownSelectionChangedEventArgs" mayBeNull="false">
/// Event arguments for the selectionChanged event
/// </param>
/// <returns />
var handler = this.get_events().getHandler('selectionChanged');
if (handler) {
handler(this, eventArgs);
}
},
add_populating : function(handler) {
/// <summary>
/// Add an event handler for the populating event
/// </summary>
/// <param name="handler" type="Function" mayBeNull="false">
/// Event handler
/// </param>
/// <returns />
this.get_events().addHandler('populating', handler);
},
remove_populating : function(handler) {
/// <summary>
/// Remove an event handler from the populating event
/// </summary>
/// <param name="handler" type="Function" mayBeNull="false">
/// Event handler
/// </param>
/// <returns />
this.get_events().removeHandler('populating', handler);
},
raisePopulating : function(eventArgs) {
/// <summary>
/// Raise the populating event
/// </summary>
/// <param name="eventArgs" type="Sys.CancelEventArgs" mayBeNull="false">
/// Event arguments for the populating event
/// </param>
/// <returns />
/// <remarks>
/// The populating event can be used to provide custom data to
/// CascadingDropDown instead of using a web service. Just cancel the
/// event (using the CancelEventArgs) and pass your own data to the
/// _setOptions method.
/// </remarks>
var handler = this.get_events().getHandler('populating');
if (handler) {
handler(this, eventArgs);
}
},
add_populated : function(handler) {
/// <summary>
/// Add an event handler for the populated event
/// </summary>
/// <param name="handler" type="Function" mayBeNull="false">
/// Event handler
/// </param>
/// <returns />
this.get_events().addHandler('populated', handler);
},
remove_populated : function(handler) {
/// <summary>
/// Remove an event handler from the populated event
/// </summary>
/// <param name="handler" type="Function" mayBeNull="false">
/// Event handler
/// </param>
/// <returns />
this.get_events().removeHandler('populated', handler);
},
raisePopulated : function(eventArgs) {
/// <summary>
/// Raise the populated event
/// </summary>
/// <param name="eventArgs" type="Sys.EventArgs" mayBeNull="false">
/// Event arguments for the populated event
/// </param>
/// <returns />
var handler = this.get_events().getHandler('populated');
if (handler) {
handler(this, eventArgs);
}
}
}
AjaxControlToolkit.CascadingDropDownBehavior.registerClass('AjaxControlToolkit.CascadingDropDownBehavior', AjaxControlToolkit.BehaviorBase);
// getDescriptor : function() {
// var td = AjaxControlToolkit.CascadingDropDownBehavior.callBaseMethod(this, 'getDescriptor');
// // Add custom properties
// td.addProperty('ParentControlID', String);
// td.addProperty('Category', String);
// td.addProperty('PromptText', String);
// td.addProperty('LoadingText', String);
// td.addProperty('ServicePath', String);
// td.addProperty('ServiceMethod', String);
// td.addProperty('SelectedValue', String);
// return td;
// },