Asp.net: no blinking linkage drop-down list control

This item has many names, links, associations, no refreshing, and no flashes... In short, it is necessary to change the value of another drop-down list with a script when the selection of a dropdownlist is changed. The current screen does not need to be submitted, so there is no flickering effect.

The solution here is to dynamically load the script:
<SCRIPT id = "ABC"/>
<Select onchange = "ABC. src = 'listdata. aspx? Xx = YY ">

In listdata. aspx? In xx = YY, JS scripts are dynamically returned based on parameters to update the specified drop-down list.

Httphandler is used to provide data, and the drop-down list data is provided by registering events in global.
To call WebService, you can call it here.

1. This control inherits dropdownlist and can be used to adjust attributes and events during design.
2. Passive dropdownlist persistence after PostBack

Add custom controls in the toolbox.
For the first time I wrote the webform Control, please provide more suggestions.