获取页面上特定类型的所有 Web 控件 [英] Get All Web Controls of a Specific Type on a Page

问题描述

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:

I have been pondering how I can get all controls on a page and then perform a task on them in this related question:

如何以编程方式搜索 C# DropDownList

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.

I need code that can scan the page, get all DropDownList Controls and return them in a list.

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.

I'm currently having to edit each individual control, I would rather be able to dynamically loop over each control to preform my task.

推荐答案

检查 我之前的 SO 答案.

基本上，这个想法是使用以下方法包装遍历控件集合的递归:

Basically, the idea is to wrap the recursion of iterating through the controls collection using :

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
}

[Edited 11/26/2013]:这是实现这一目标的更优雅的方式.我写了两个扩展方法，可以双向遍历控制树.这些方法是用更 Linq 的方式编写的，因为它产生了一个可枚举的:

: here is a more elegant way to reach this goal. I wrote two extensions methods that can walk the control tree in both directions. The methods are written in a more Linq way as it produces an enumerable:

/// <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.

Thanks to the this keyword, these methods are extensions methods and can simplify the code.

例如，要查找页面中的所有DropDownList，只需调用:

For example, to find all DropDownList in the page, you can simply call:

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

因为使用了 yield 关键字，并且因为 Linq 足够聪明，可以推迟枚举的执行，您可以调用(例如):

Because of the use of the yield keyword, and because Linq is smart enough to defer execution of the enumeration, you can call (for example):

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

只要满足 First 方法中的谓词，枚举就会停止.不会遍历整个控制树.

The enumeration will stop as soon as the predicate in the First method is satisfied. The whole control tree won't be walked.

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