c# - 获取页面上特定类型的所有 Web 控件

Question

我一直在思考如何获取页面上的所有控件，然后在这个相关问题中对它们执行任务:

How to Search Through a C# DropDownList Programmatically

我需要可以扫描页面、获取所有 DropDownList 控件并将它们返回到列表中的代码。

我目前必须编辑每个单独的控件，我宁愿能够动态循环每个控件来执行我的任务。

Answer 1

检查 my previous SO answer .

基本上，我们的想法是使用以下方法包装迭代控件集合的递归:

private void GetControlList<T>(ControlCollection controlCollection, List<T> resultCollection)
where T : Control
{
    foreach (Control control in controlCollection)
    {
        //if (control.GetType() == typeof(T))
        if (control is T) // This is cleaner
            resultCollection.Add((T)control);

        if (control.HasControls())
            GetControlList(control.Controls, resultCollection);
    }
}

并使用它:

List<DropDownList> allControls = new List<DropDownList>();
GetControlList<DropDownList>(Page.Controls, allControls )
foreach (var childControl in allControls )
{
//     call for all controls of the page
}

[2013 年 11 月 26 日编辑]:这是实现此目标的更优雅的方法。我写了两个可以在两个方向上遍历控制树的扩展方法。这些方法以更 Linq 的方式编写，因为它生成可枚举的:

/// <summary>
/// Provide utilities methods related to <see cref="Control"/> objects
/// </summary>
public static class ControlUtilities
{
    /// <summary>
    /// Find the first ancestor of the selected control in the control tree
    /// </summary>
    /// <typeparam name="TControl">Type of the ancestor to look for</typeparam>
    /// <param name="control">The control to look for its ancestors</param>
    /// <returns>The first ancestor of the specified type, or null if no ancestor is found.</returns>
    public static TControl FindAncestor<TControl>(this Control control) where TControl : Control
    {
        if (control == null) throw new ArgumentNullException("control");

        Control parent = control;
        do
        {
            parent = parent.Parent;
            var candidate = parent as TControl;
            if (candidate != null)
            {
                return candidate;
            }
        } while (parent != null);
        return null;
    }

    /// <summary>
    /// Finds all descendants of a certain type of the specified control.
    /// </summary>
    /// <typeparam name="TControl">The type of descendant controls to look for.</typeparam>
    /// <param name="parent">The parent control where to look into.</param>
    /// <returns>All corresponding descendants</returns>
    public static IEnumerable<TControl> FindDescendants<TControl>(this Control parent) where TControl : Control
    {
        if (parent == null) throw new ArgumentNullException("control");

        if (parent.HasControls())
        {
            foreach (Control childControl in parent.Controls)
            {
                var candidate = childControl as TControl;
                if (candidate != null) yield return candidate;

                foreach (var nextLevel in FindDescendants<TControl>(childControl))
                {
                    yield return nextLevel;
                }
            }
        }
    }
}

感谢this关键字，这些方法都是扩展方法，可以简化代码。

例如，要查找页面中的所有DropDownList，您可以简单地调用:

var allDropDowns = this.Page.FindControl<DropDownList>();

由于使用了 yield 关键字，并且因为 Linq 足够智能可以推迟枚举的执行，您可以调用(例如):

var allDropDowns = this.Page.FindDescendants<DropDownList>();
var firstDropDownWithCustomClass = allDropDowns.First(
    ddl=>ddl.CssClass == "customclass"
    );

一旦 First 方法中的谓词得到满足，枚举就会停止。不会遍历整个控制树。