在自定义控件中从javascript调用c＃方法 [英] call c# method from javascript in custom control

问题描述

我正在尝试创建一个继承自checkboxlist控件的Multi Select下拉列表自定义控件。它有一个title属性，它将被设置为div标签中呈现的下拉控件的默认文本，其中的图像显示下拉图标，如下面的代码所示。我还嵌入了一个javascript函数，它将事件监听器附加到渲染的checkboxlist复选框。我想要做的是，当复选框选中状态更改时，应该从javascript设置Title属性。或者应该调用c＃方法，以便可以设置Title属性。请指导我如何做到这一点。



我的自定义控制代码

I am trying to create a Multi Select dropdown list custom control inheriting from the checkboxlist control. it has a title property which will be set as the default text of the dropdown control rendered in a div tag with an image to show dropdown icon as in the code below. I also have a javascript function embedded which will attach event listener to the rendered checkboxlist checkboxes. What i want to do is, when the checkbox checked state is changed the Title property should be set from the javascript . or a c# method should be called so that Title property can be set. Please guide me on how this can be done.

my custom control code

[ToolboxData("<{0}:CheckBoxDropDown  runat="server"></{0}:CheckBoxDropDown>")]
    public class CheckBoxDropDown : CheckBoxList
    {
public string Title { get; set; }

 protected override void Render(HtmlTextWriter writer)
        {
 string divFirstRow = @" <div id='{3}'> {0} <img id=""{1}"" src=""{2}""/></div>";

            writer.WriteLine(string.Format("<div class=\"{0}\" >", this.CssClass));

 writer.Write(string.Format(divFirstRow, this.Title + "  ",
        base.ClientID + "_arrowDown", ImageURL, base.ClientID + "_Title"));
            writer.WriteLine();

base.Render(writer); //render the checkboxlist under the div

            writer.WriteLine("</div>");

这是我从自定义控件渲染的javascript代码。

this is my javascript code that is rendered from the custom control.

window.onload = function () {
            for ( i = 0; i < checkbox.length; i++) {
                checkbox[i].attachEvent(""onclick"", checkChanged );
            }
        }


            function checkChanged() {
                strTitle='';
             for ( i = 0; i < checkbox.length; i++) {
                if(checkbox[i].checked==true)
                {
                      strTitle+=checkbox[i].value+ ";";
                }
                }
                CHK.Title=strTitle; // This has error
            }

我在strTitle中获得所选的值。但无法将其设置为Title属性。

I get the selected values in strTitle. but not able to set it as the Title property.

推荐答案

在Render方法中，您可以使用getElementById添加具有特定id的title元素，以便从JavaScript引用。此外，对于每个复选框或选择控件，您可以添加onchange事件属性，该属性将在选择更改时调用所需的JavaScript函数。 onchange属性可以在Render方法中添加文本字符串。同样在MSDN上查询：

In your Render method you could add the title element with a specific id to reference from JavaScript using getElementById. Also for each checkbox or select control you can add an onchange event attribute that will call the required JavaScript function when the selection changes. The onchange attribute could be added text string within your Render method. Also on MSDN look up:

AddAttributesToRender

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