根据另一个控件的 ControlId 设置 WebControls TabIndex

Question

我有一个 ASP.NET Webforms 站点，经常添加功能。 大多数情况下，新的 WebControl 会添加到页面中，并且我需要将 TabIndex 增加到页面上的所有后续控件。

我更喜欢一个更强大的解决方案，而不是在初始分配的选项卡索引之间选择任意间隙。使用设计器选项卡顺序功能设置选项卡索引是一种选择，但我更愿意保留在源视图中。

理想情况下，例如，如果我有三个复选框，我希望能够根据先前的控件选项卡索引定义选项卡索引。然后我只需要插入新控件并更改一个现有控件。

例如，向 WebControl 添加新属性 TabIndexAfterControlId：

<asp:CheckBox ID="checkBoxA" runat="server" TabIndex="1"/>
<asp:CheckBox ID="checkBoxB" runat="server" TabIndexAfterControlId="checkBoxA"/>
<asp:CheckBox ID="checkBoxC" runat="server" TabIndexAfterControlId="checkBoxB"/>

我的第一个想法是使用新属性扩展 System.Web.UI.WebControls.WebControl，但是 不支持扩展属性。

Answer 1

注意：此方法适用于某些 Web 控件（DropDownList），但不适用于所有 Web 控件（复选框）。我将其留在这里供参考。

我最终得到了一个解决方案，该解决方案使用代码隐藏方法来捕获控件之间的关系。

<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) %>'/>

后面的代码方法最初将执行基本的 TabIndex 分配，当 Tab 键顺序遵循页面上控件的顺序时，该分配效果很好。然后在 PreRender 事件期间，将再次检查选项卡索引顺序。如果 Tab 键顺序不遵循页面的自然流程，这一点很重要。

    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;
        }

    }

Answer 2

当某些控件无法绑定 TabIndex (CheckBox) 时，我之前尝试使用数据绑定语法 (<%# ... %>) 为 Web 控件设置 TabIndex 失败。它也不理想，因为我需要将对当前控件的引用传递到代码隐藏方法中。

这次我使用了一个自定义的 ExpressionBuilder ，它接受以下名称：当前控件应遵循 Tab 键顺序的 Web 控件。

TabIndexAfterExpressionBuilder 最初返回短值 -1 作为值。同时注册当前Page的LoadComplete事件。当此事件触发时，将找到两个控件，并根据其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;
            }

        }
    }
}

web.config

<system.web>
    <compilation debug="true" targetFramework="4.0">
        <expressionBuilders>
            <add expressionPrefix="TabIndex" type="ExpressionBuilders.TabIndexExpressionBuilder, ExpressionBuilders"/>
        </expressionBuilders>
    </compilation>
</system.web>