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一、引出Ajax的自动完成
现在要实现一个员工信息查询的功能,即根据输入的名字检索员工的详细信息。这是一个简单的数据表查询,在ASP.NET中实现这样的功能是比较简单的.
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从上面可以看出,这种员工信息查询功能还存在一些不足,比如用户可能记不全员工的名字,只记得前面几个字母是什么,这样用户只能根据记忆猜测,一遍遍地尝试。如果在用户输入的同时,输入框下方可以给出相应的提示,辅助用户输入,那么用户进行检索的速度和成功率就会大大提高.这就是基于Ajax的自动完成功能.
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二、自动完成功能的实现
实现这样的功能需要按以下的步骤进行。
· 服务器端提供GetSearchItems方法给客户端,用来返回满足条件的员工列表。
· 客户端的输入框需要增加onkeydown响应函数,以便即时获取满足条件的员工列表。
· 通过客户端的JavaScript动态列出待选结果的列表,同时还要提供键盘和鼠标的响应。
三、服务器端实现
本文采用AjaxPro.NET作为Ajax开发框架,首先为使用AjaxPro.NET做一些准备工作。 添加对AjaxPro.dll的引用,修改Web.config配置文件,在system.web节点下加入如下配置:
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<httpHandlers>
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<!-- Register the ajax handler -->
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<add verb="POST,GET" path="ajaxpro/*.ashx" type="AjaxPro.AjaxHandlerFactory, AjaxPro" />
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</httpHandlers>
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在页面后台代码(Default.aspx.cs)的Page_Load方法中增加下面的代码:
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protected void Page_Load(object sender, EventArgs e)
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{
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AjaxPro.Utility.RegisterTypeForAjax(typeof(_Default));
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}
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下面定义提供给客户端调用的方法GetSearchItems(),参数query为模糊查询的关键字值:
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[AjaxPro.AjaxMethod()]
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public ArrayList GetSearchItems(string query)
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{
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ArrayList items = new ArrayList();
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StringBuilder queryString = new StringBuilder();
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queryString.Append("select employeeid,lastname,firstname,title,titleofcourtesy from dbo.Employees");
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queryString.Append(" where firstname like '%" + query + "%'");
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DataSet ds = DataBase.Instance.ReturnDataSet(queryString.ToString());
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for (int i = 0; i < ds.Tables[0].Rows.Count; i++)
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{
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items.Add(ds.Tables[0].Rows[i][2].ToString());
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}
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return items;
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}
GetSearchItems方法返回一个ArrayList对象,它将包含所有以用户输入字符串的员工名字。
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四、客户端实现
相对于服务器端的方法而言,客户端的处理要复杂得多。首先来分析如何根据服务器端返回的ArrayList对象展示结果。这里用到了Web编程中“层”(div)的概念,通过JavaScript和DOM创建一个新的层div,将ArrayList中的每一个条目都作为其子节点加入到div中,而每一个条目也被看作是一个div,其中具体的文本内容则是一个span对象。
除了显示待选的结果之外,下拉区域还要对键盘、鼠标事件做出响应;为了实时地显示待选结果,还需要定时更新待选结果的列表。这些功能都封装在lookup.js中。下面是lookeu.js的定义:
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// 下拉区背景色
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var DIV_BG_COLOR = "#EEE";
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// 高亮显示条目颜色
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var DIV_HIGHLIGHT_COLOR = "#C30";
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// 字体
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var DIV_FONT = "Arial";
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// 下拉区内补丁大小
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var DIV_PADDING = "2px";
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// 下拉区边框样式
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var DIV_BORDER = "1px solid #CCC";
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// 文本输入框
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var queryField;
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// 下拉区id
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var divName;
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// IFrame名称
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var ifName;
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// 记录上次选择的值
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var lastVal = "";
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// 当前选择的值
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var val = "";
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// 显示结果的下拉区
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var globalDiv;
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// 下拉区是否设置格式的标记
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var divFormatted = false;
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/**
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InitQueryCode函数必须在<body onload>事件的响应函数中调用,其中:
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queryFieldName为文本框控件的id,
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hiddenDivName为显示下拉区div的id
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*/
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function InitQueryCode (queryFieldName, hiddenDivName)
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{
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// 指定文本输入框的onblur和onkeydown响应函数
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queryField = document.getElementById(queryFieldName);
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queryField.onblur = hideDiv;
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queryField.onkeydown = keypressHandler;
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// 设置queryField的autocomplete属性为"off"
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queryField.autocomplete = "off";
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// 如果没有指定hiddenDivName,取默认值"querydiv"
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if (hiddenDivName)
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{
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divName = hiddenDivName;
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}
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else
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{
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divName = "querydiv";
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}
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// IFrame的name
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ifName = "queryiframe";
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// 100ms后调用mainLoop函数
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setTimeout("mainLoop()", 100);
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}
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/**
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获取下拉区的div,如果没有则创建之
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*/
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function getDiv (divID)
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{
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if (!globalDiv)
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{
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// 如果div在页面中不存在,创建一个新的div
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if (!document.getElementById(divID))
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{
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var newNode = document.createElement("div");
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newNode.setAttribute("id", divID);
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document.body.appendChild(newNode);
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}
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// globalDiv设置为div的引用
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globalDiv = document.getElementById(divID);
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// 计算div左上角的位置
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var x = queryField.offsetLeft;
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var y = queryField.offsetTop + queryField.offsetHeight;
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var parent = queryField;
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while (parent.offsetParent)
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{
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parent = parent.offsetParent;
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x += parent.offsetLeft;
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y += parent.offsetTop;
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}
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// 如果没有对div设置格式,则为其设置相应的显示样式
91
if (!divFormatted)
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{
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globalDiv.style.backgroundColor = DIV_BG_COLOR;
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globalDiv.style.fontFamily = DIV_FONT;
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globalDiv.style.padding = DIV_PADDING;
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globalDiv.style.border = DIV_BORDER;
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globalDiv.style.width = "100px";
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globalDiv.style.fontSize = "90%";
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globalDiv.style.position = "absolute";
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globalDiv.style.left = x + "px";
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globalDiv.style.top = y + "px";
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globalDiv.style.visibility = "hidden";
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globalDiv.style.zIndex = 10000;
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divFormatted = true;
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}
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}
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return globalDiv;
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}
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/**
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根据返回的结果集显示下拉区
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*/
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function showQueryDiv(resultArray)
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{
118
// 获取div的引用
119
var div = getDiv(divName);
120
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// 如果div中有内容,则删除之
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while (div.childNodes.length > 0)
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div.removeChild(div.childNodes[0]);
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// 依次添加结果
126
for (var i = 0; i < resultArray.length; i++)
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{
128
// 每一个结果也是一个div
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var result = document.createElement("div");
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// 设置结果div的显示样式
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result.style.cursor = "pointer";
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result.style.padding = "2px 0px 2px 0px";
133
// 设置为未选中
134
_unhighlightResult(result);
135
// 设置鼠标移进、移出等事件响应函数
136
result.onmousedown = selectResult;
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result.onmouseover = highlightResult;
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result.onmouseout = unhighlightResult;
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// 结果的文本是一个span
141
var result1 = document.createElement("span");
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// 设置文本span的显示样式
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result1.className = "result1";
144
result1.style.textAlign = "left";
145
result1.style.fontWeight = "bold";
146
result1.innerHTML = resultArray[i];
147
148
// 将span添加为结果div的子节点
149
result.appendChild(result1);
150
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// 将结果div添加为下拉区的子节点
152
div.appendChild(result);
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}
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// 如果结果集不为空,则显示,否则不显示
156
showDiv(resultArray.length > 0);
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}
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/**
160
用户点击某个结果时,将文本框的内容替换为结果的文本,
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并隐藏下拉区
162
*/
163
function selectResult()
164
{
165
_selectResult(this);
166
}
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// 选择一个条目
169
function _selectResult(item)
170
{
171
var spans = item.getElementsByTagName("span");
172
if (spans)
173
{
174
for (var i = 0; i < spans.length; i++)
175
{
176
if (spans[i].className == "result1")
177
{
178
queryField.value = spans[i].innerHTML;
179
lastVal = val = escape(queryField.value);
180
mainLoop();
181
queryField.focus();
182
showDiv(false);
183
return;
184
}
185
}
186
}
187
}
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/**
190
当鼠标移到某个条目之上时,高亮显示该条目
191
*/
192
function highlightResult()
193
{
194
_highlightResult(this);
195
}
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function _highlightResult(item)
198
{
199
item.style.backgroundColor = DIV_HIGHLIGHT_COLOR;
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}
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/**
203
当鼠标移出某个条目时,正常显示该条目
204
*/
205
function unhighlightResult()
206
{
207
_unhighlightResult(this);
208
}
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210
function _unhighlightResult(item)
211
{
212
item.style.backgroundColor = DIV_BG_COLOR;
213
}
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215
/**
216
显示/不显示下拉区
217
*/
218
function showDiv (show)
219
{
220
var div = getDiv(divName);
221
if (show)
222
{
223
div.style.visibility = "visible";
224
}
225
else
226
{
227
div.style.visibility = "hidden";
228
}
229
//adjustiFrame();
230
}
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/**
233
隐藏下拉区
234
*/
235
function hideDiv ()
236
{
237
showDiv(false);
238
}
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/**
241
调整IFrame的位置,这是为了解决div可能会显示在输入框后面的问题
242
*/
243
function adjustiFrame()
244
{
245
// 如果没有IFrame,则创建之
246
if (!document.getElementById(ifName))
247
{
248
var newNode = document.createElement("iFrame");
249
newNode.setAttribute("id", ifName);
250
newNode.setAttribute("src", "javascript:false;");
251
newNode.setAttribute("scrolling", "no");
252
newNode.setAttribute("frameborder", "0");
253
document.body.appendChild(newNode);
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}
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iFrameDiv = document.getElementById(ifName);
257
var div = getDiv(divName);
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259
// 调整IFrame的位置与div重合,并在div的下一层
260
try
261
{
262
iFrameDiv.style.position = "absolute";
263
iFrameDiv.style.width = div.offsetWidth;
264
iFrameDiv.style.height = div.offsetHeight;
265
iFrameDiv.style.top = div.style.top;
266
iFrameDiv.style.left = div.style.left;
267
iFrameDiv.style.zIndex = div.style.zIndex - 1;
268
iFrameDiv.style.visibility = div.style.visibility;
269
}
270
catch (e)
271
{
272
}
273
}
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275
/**
276
文本输入框的onkeydown响应函数
277
*/
278
function keypressHandler (evt)
279
{
280
// 获取对下拉区的引用
281
var div = getDiv(divName);
282
283
// 如果下拉区不显示,则什么也不做
284
if (div.style.visibility == "hidden")
285
{
286
return true;
287
}
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// 确保evt是一个有效的事件
290
if (!evt && window.event)
291
{
292
evt = window.event;
293
}
294
var key = evt.keyCode;
295
296
var KEYUP = 38;
297
var KEYDOWN = 40;
298
var KEYENTER = 13;
299
var KEYTAB = 9;
300
301
// 只处理上下键、回车键和Tab键的响应
302
if ((key != KEYUP) && (key != KEYDOWN) && (key != KEYENTER) && (key != KEYTAB))
303
{
304
return true;
305
}
306
307
var selNum = getSelectedSpanNum(div);
308
var selSpan = setSelectedSpan(div, selNum);
309
310
// 如果键入回车和Tab,则选择当前选择条目
311
if ((key == KEYENTER) || (key == KEYTAB))
312
{
313
if (selSpan)
314
{
315
_selectResult(selSpan);
316
}
317
evt.cancelBubble = true;
318
return false;
319
}
320
else //如果键入上下键,则上下移动选中条目
321
{
322
if (key == KEYUP)
323
{
324
selSpan = setSelectedSpan(div, selNum - 1);
325
}
326
if (key == KEYDOWN)
327
{
328
selSpan = setSelectedSpan(div, selNum + 1);
329
}
330
if (selSpan)
331
{
332
_highlightResult(selSpan);
333
}
334
}
335
336
// 显示下拉区
337
showDiv(true);
338
return true;
339
}
340
341
/**
342
获取当前选中的条目的序号
343
*/
344
function getSelectedSpanNum(div)
345
{
346
var count = -1;
347
var spans = div.getElementsByTagName("div");
348
if (spans)
349
{
350
for (var i = 0; i < spans.length; i++)
351
{
352
count++;
353
if (spans[i].style.backgroundColor != div.style.backgroundColor)
354
{
355
return count;
356
}
357
}
358
}
359
360
return -1;
361
}
362
363
/**
364
选择指定序号的结果条目
365
*/
366
function setSelectedSpan(div, spanNum)
367
{
368
var count = -1;
369
var thisSpan;
370
var spans = div.getElementsByTagName("div");
371
if (spans)
372
{
373
for (var i = 0; i < spans.length; i++)
374
{
375
if (++count == spanNum)
376
{
377
_highlightResult(spans[i]);
378
thisSpan = spans[i];
379
}
380
else
381
{
382
_unhighlightResult(spans[i]);
383
}
384
}
385
}
386
387
return thisSpan;
388
}
389
InitQueryCode函数必须在页面的onload响应中执行,该函数最后调用setTimeout方法执行了mainLoop方法。注意,mainLoop方法并没有在lookup.js中定义,必须在包含lookup.js文件的页面文件中增加该函数的定义。于此,我们就需要在Default.aspx页面上加入如下定义:
2
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3
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4
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5
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6
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7
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8
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9
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10
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11
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12
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13
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14
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15
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16
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17
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18
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19
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20
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21
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22
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23
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24
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25
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26
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27
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28
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29
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30
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32
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33
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34
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35
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36
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37
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38
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39
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40
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41
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42
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43
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44
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45
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46
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47
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48
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49
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50
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51
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52
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53
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54
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55
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56
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57
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58
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59
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60
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61
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62
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63
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64
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65
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66
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67
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68
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69
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70
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71
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72
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73
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74
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75
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76
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77
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78
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79
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80
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81
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82
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83
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84
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85
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86
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87
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88
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89
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90
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91
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92
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93
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94
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95
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96
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97
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98
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99
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100
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101
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102
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<script language="javascript" src="lookup.js"></script>
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<script language="javascript">
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mainLoop = function()
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{
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val = escape(queryField.value);
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if (lastVal != val)
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{
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var response = _Default.GetSearchItems(val);
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showQueryDiv(response.value);
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lastVal = val;
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}
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setTimeout('mainLoop()', 100);
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return true;
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}
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</script>
由上述代码可以看到mainLoop函数每隔100ms会执行一次,它会判断当前文本输入框的值和上次提交查询的值是否相同,如果不同,它会重新向服务器发送请求进行查询,并且更新下拉区域的显示。
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于此,一个基于 Ajax的自动完成功能就实现了。
本文借鉴于《ajax web2.0快速入门与项目实践》。
这本书上还使用了控件将该功能进行了封装,这样要实现Ajax的自动完成功能就更加方便了。在此就不做过多解说。
本文示例代码下载:AutoComplete.rar
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