我有一个ASP.NET Web表单的网站会定期有功能补充说。 大多数时间一个新的Web控件添加到页面，我需要tabindex属性递增到页面上的所有后续的控制。
我宁愿比选择初始分配的标签索引之间的任意间隙更强大的解决方案。 设置使用设计选项卡顺序功能的标签索引是一种选择，但我更愿意留在源视图。
理想情况下，如果我有，例如，三个复选框我希望能够定义基于取消了原来的控制tabindex属性tabindex属性。 然后，我只需要插入新的控制和改变一个现有的控制。
例如，添加一个新的属性TabIndexAfterControlId到Web控件：
<asp:CheckBox ID="checkBoxA" runat="server" TabIndex="1"/>
<asp:CheckBox ID="checkBoxB" runat="server" TabIndexAfterControlId="checkBoxA"/>
<asp:CheckBox ID="checkBoxC" runat="server" TabIndexAfterControlId="checkBoxB"/>
我首先想到的是用System.Web.UI.WebControls.WebControl新属性扩展，但是扩展性不支持 。
注意：此方法做过一段器WebControls（DropDownLists），但不是所有的人（的CheckBox）。 我离开这里以供参考。
我已经结束了与使用代码隐藏方法来捕获控制之间的关系的解决方案。
<asp:CheckBox ID="checkBoxA" runat="server" TabIndex="1"/>
<asp:CheckBox ID="checkBoxB" runat="server" TabIndex='<%# TabIndexAfter(checkBoxB, checkBoxA) %>'/>
<asp:CheckBox ID="checkBoxC" runat="server" TabIndex='<%# TabIndexAfter(checkBoxC, checkBoxB) %>'/>
后面的方法中的代码将首先做一个基本的TabIndex分配，当标签顺序遵循控件的页面上的顺序效果很好。 然后PreRender事件期间的标签索引顺序将再次检查。 如果标签顺序不不按照页面的自然流动，这是非常重要的。
private LinkedList<WebControl> _webControlTabOrder;
/// <summary>
/// Assign the current WebControl TabIndex a value greater than the prior WebControl.
/// </summary>
/// <param name="currentWebControl">The current WebControl to set the TabIndex for</param>
/// <param name="priorWebControl">The prior WebControl to get the previous TabIndex from.</param>
/// <returns>The new TabIndex for the control</returns>
public int TabIndexAfter(WebControl currentWebControl, WebControl priorWebControl)
{
if (_webControlTabOrder == null)
{
_webControlTabOrder = new LinkedList<WebControl>();
this.PreRender += new EventHandler(UserControlBase_PreRender);
}
LinkedListNode<WebControl> priorNode = _webControlTabOrder.Find(currentWebControl);
if (priorNode == null)
{
priorNode = _webControlTabOrder.AddLast(priorWebControl);
}
_webControlTabOrder.AddAfter(priorNode, currentWebControl);
return priorWebControl.TabIndex + 1;
}
void UserControlBase_PreRender(object sender, EventArgs e)
{
LinkedListNode<WebControl> currentNode = _webControlTabOrder.First;
while(currentNode.Next != null)
{
LinkedListNode<WebControl> nextNode = currentNode.Next;
if (nextNode.Value.TabIndex <= currentNode.Value.TabIndex)
{
nextNode.Value.TabIndex = (short)(currentNode.Value.TabIndex + 1);
}
currentNode = nextNode;
}
}
当一些控制将不绑定的TabIndex（复选框）使用数据绑定语法（<％＃...％>）来设置Web控件的TabIndex我之前尝试失败。 它也是不理想的，因为我需要电流控制的参考传递到后面方法的代码。
这一次我去一个自定义的ExpressionBuilder接受电流控制应在标签顺序遵循Web控件的名称。
所述TabIndexAfterExpressionBuilder最初返回短-1作为值。 同时，它与当前页的LoadComplete事件进行注册。 当此事件触发这两个控件都发现标签索引根据它们的相对位置设置。
使用tabIndex表达式生成器实例器WebControls
<asp:TextBox ID="txtTextBox0" runat="server" TabIndex="1" /><br />
<asp:TextBox ID="txtTextBox1" runat="server" TabIndex="<%$ TabIndex:txtTextBox0 %>" /><br />
<asp:TextBox ID="txtTextBox2" runat="server" TabIndex="<%$ TabIndex:txtTextBox1 %>" />
TabIndexExpressionBuilder.cs
namespace ExpressionBuilders
{
public class TabIndexExpressionBuilder : ExpressionBuilder
{
public override System.CodeDom.CodeExpression GetCodeExpression(System.Web.UI.BoundPropertyEntry entry, object parsedData, ExpressionBuilderContext context)
{
string priorControlId = entry.Expression.Trim();
string currentControlId = entry.ControlID;
CodeExpression[] inputParams = new CodeExpression[] { new CodePrimitiveExpression(priorControlId),
new CodePrimitiveExpression(currentControlId),
new CodeTypeOfExpression(entry.DeclaringType),
new CodePrimitiveExpression(entry.PropertyInfo.Name) };
// Return a CodeMethodInvokeExpression that will invoke the GetRequestedValue method using the specified input parameters
return new CodeMethodInvokeExpression(new CodeTypeReferenceExpression(this.GetType()),
"GetRequestedValue",
inputParams);
}
public static object GetRequestedValue(string priorControlId, string currentControlId, Type targetType, string propertyName)
{
if (HttpContext.Current == null)
{
return null;
}
Page page = HttpContext.Current.Handler as Page;
if (page != null)
{
page.LoadComplete += delegate(object sender, EventArgs e)
{
WebControl currentWebControl = FindControlRecursive(page, currentControlId);
WebControl priorWebControl = FindControlRecursive(page, priorControlId);
if (currentWebControl != null && priorWebControl != null)
{
TabIndexAfter(page, currentWebControl, priorWebControl);
}
};
}
// Default TabIndex
short value = (short)-1;
return value;
}
private static WebControl FindControlRecursive(Control rootControl, string controlID)
{
if (rootControl.ID == controlID) { return rootControl as WebControl; }
foreach (Control controlToSearch in rootControl.Controls)
{
Control controlToReturn = FindControlRecursive(controlToSearch, controlID);
if (controlToReturn != null)
{
return controlToReturn as WebControl;
}
}
return null;
}
#region Tabbing
/// <summary>
/// Assign the current WebControl TabIndex a value greater than the prior WebControl.
/// </summary>
/// <param name="currentWebControl">The current Control to set the TabIndex for</param>
/// <param name="priorWebControl">The prior Control to get the previous TabIndex from.</param>
/// <returns>The new TabIndex for the current control</returns>
private static short TabIndexAfter(Page page, WebControl currentWebControl, object prior)
{
TabOrderWebControl tabOrderWebControl = page.FindControl("TabOrderWebControl") as TabOrderWebControl;
if (tabOrderWebControl == null)
{
tabOrderWebControl = new TabOrderWebControl();
page.Controls.Add(tabOrderWebControl);
}
WebControl priorWebControl = prior as WebControl;
if (priorWebControl == null)
{
string priorWebControlId = prior as string;
priorWebControl = page.FindControl(priorWebControlId) as WebControl;
}
if (currentWebControl == null) { throw new ArgumentNullException("currentWebControl"); }
if (priorWebControl == null) { throw new ArgumentNullException("priorWebControl"); }
if (currentWebControl == priorWebControl) { throw new ArgumentException("priorWebControl is the same as the currentWebControl", "priorWebControl"); }
tabOrderWebControl.TabIndexAfter(currentWebControl, priorWebControl);
return currentWebControl.TabIndex;
}
#endregion
}
}
TabOrderWebControl.cs
namespace ExpressionBuilders
{
public class TabOrderWebControl :
WebControl
{
LinkedList<WebControl> _webControlTabOrder;
internal void TabIndexAfter(System.Web.UI.WebControls.WebControl currentWebControl, System.Web.UI.WebControls.WebControl priorWebControl)
{
if (_webControlTabOrder == null)
{
_webControlTabOrder = new LinkedList<WebControl>();
this.Page.PreRender += new EventHandler(PageBase_PreRender);
}
LinkedListNode<WebControl> priorNode = _webControlTabOrder.Find(priorWebControl);
LinkedListNode<WebControl> currentNode = _webControlTabOrder.Find(currentWebControl);
if (currentNode != null)
{
//The current node is already in the list (it must preceed some other control)
//Add the prior node before it.
if (priorNode == null)
{
priorNode = _webControlTabOrder.AddBefore(currentNode, priorWebControl);
}
else
{
//Both nodes are already in the list. Ensure the ordering is correct.
bool foundPriorNode = false;
foreach (WebControl controlNode in _webControlTabOrder)
{
if (controlNode == priorWebControl)
{
foundPriorNode = true;
}
else if (controlNode == currentWebControl)
{
if (foundPriorNode)
{
//Ordering is correct
break;
}
else
{
throw new ApplicationException(string.Format("WebControl ordering is incorrect. Found {1} before {0}", currentWebControl.ID, priorWebControl.ID));
}
}
}
}
}
else if (priorNode == null)
{
//Neither control is in the list yet.
priorNode = _webControlTabOrder.AddLast(priorWebControl);
currentNode = _webControlTabOrder.AddAfter(priorNode, currentWebControl);
}
else
{
//Prior node is already in the list but the current node isn't
currentNode = _webControlTabOrder.AddAfter(priorNode, currentWebControl);
}
}
/// <summary>
/// Once all the controls have been added to the linked list ensure the tab ordering is correct.
/// </summary>
/// <param name="sender"></param>
/// <param name="e"></param>
void PageBase_PreRender(object sender, EventArgs e)
{
AssignTabIndexes();
}
/// <summary>
/// Reassign tab indexes for all known controls.
/// </summary>
protected void AssignTabIndexes()
{
LinkedListNode<WebControl> currentNode = _webControlTabOrder.First;
while (currentNode.Next != null)
{
LinkedListNode<WebControl> nextNode = currentNode.Next;
WebControl currentControl = currentNode.Value;
WebControl nextControl = nextNode.Value;
if (currentControl == nextControl)
{
throw new ApplicationException("Control added twice");
}
short currentTabIndex = currentControl.TabIndex;
short nextTabIndex = nextControl.TabIndex;
if (nextTabIndex <= currentTabIndex)
{
nextControl.TabIndex = (short)(currentTabIndex + 1);
}
currentNode = nextNode;
}
}
}
}
web.config中
<system.web>
<compilation debug="true" targetFramework="4.0">
<expressionBuilders>
<add expressionPrefix="TabIndex" type="ExpressionBuilders.TabIndexExpressionBuilder, ExpressionBuilders"/>
</expressionBuilders>
</compilation>
</system.web>
