我之前尝试使用数据绑定语法 (<%# ... %>) 为 Web 控件设置 TabIndex 失败，因为某些控件不会绑定 TabIndex (CheckBox)。这也不是很理想，因为我需要将对当前控件的引用传递到代码隐藏方法中。
这一次，我使用了一个自定义ExpressionBuilder，它接受当前控件应按 Tab 键顺序跟随的 Web 控件的名称。
TabIndexAfterExpressionBuilder 最初返回短 -1 作为值。同时它注册到当前 Page 的 LoadComplete 事件。当此事件触发时，会找到两个控件并根据它们的相对位置设置选项卡索引。
使用 TabIndex 表达式生成器的示例 WebControl
<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;
}
}
}
}
网络配置
<system.web>
<compilation debug="true" targetFramework="4.0">
<expressionBuilders>
<add expressionPrefix="TabIndex" type="ExpressionBuilders.TabIndexExpressionBuilder, ExpressionBuilders"/>
</expressionBuilders>
</compilation>
</system.web>