ID,ClientIDandUniqueID的区别 jquery uniqueid

I this post I will try to explain thedifference between those three commonly used properties. Eachproperty is described in a separate section. Attached you can finda sample web site as well as two screenshots visually depicting thedifference between the ID, ClientID and UniqueIDproperties.

ID
The ID property is used to assign an identifier to an ASP.NETserver control which can be later used to access that control. Youcan use either the field generated in the codebehind or pass thevalue of the ID property to the FindControl method. There is acatch though - the ID property is unique only within the currentNamingContainer (page, user control, control with item templateetc). If a server control is defined inside the item template ofsome other control (Repeater, DataGrid) or user control, its IDproperty is no longer unique. For example, you can add some usercontrol twice in the same page. Any child controls of that usercontrol will have the same ID. Also the ASP.NET page parser won'tgenerate a codebehind field corresponding to the control ID in casethe control is defined inside a template. This is the reason youcannot easily find a specific control when it is part of a template- you need to use the FindControl method of its container controlinstead. As a side note, setting the ID property is not mandatory.If you don't set it the ASP.NET Runtime will generate one for youin the form of "_ctl0", "_ctl1", etc.

UniqueID
The UniqueID property is the page-wide unique identifier of anASP.NET server control. Its uniqueness is guaranteed by prefixingthe ID of a server control with the ID of its NamingContainer. Ifthe NamingContainer is the Page the UniqueID will remain the sameas the ID.

For example if a Label with ID="Label1"is defined in a user control with ID = "UserControl1" the UniqueIDof the Label will be "UserControl1$Label1". Adding another instanceof the same user control (with ID = "UserControl2") will make theUniqueID of its child label to be "UserControl2$Label1".

The UniqueID propertyis also used to provide value for the HTML "name" attribute ofinput fields (checkboxes, dropdown lists, and hidden fields).UniqueID also plays major role in postbacks. The UniqueID propertyof a server control, which supports postbacks, provides data forthe __EVENTTARGET hidden field. The ASP.NET Runtime then uses the__EVENTTARGET field to find the control which triggered thepostback and then calls its RaisePostBackEvent method. Here is somecode which illustrates the idea:

IPostBackEventHandlerpostBackInitiator =

Page.FindControl(Request.Form["__EVENTTARGET") AsIPostBackEventHandler;

if (postBackInitiator!= null)
postBackInitiator.RaisePostBackEvent(Request.Form["__EVENTARGUMENT"]);

You can use theUniqueID property to find any control no matter how deep it isnested in the control hierarchy. Just pass its value to theFindControl method of the Page.

ClientID
The ClientID property is quite similar to the UniqueID. It isgenerated following the same rules (the ID of the control prefixedby the ID of its NamingContainer). The only difference is theseparator - for the ClientID it is the "_" (underscore)symbol.
The ClientID property is globally unique amongall controls defined in an ASP.NET page. You may ask why we needtwo different globally unique properties. The answer is thatClientID serves a different purpose than UniqueID. In most servercontrols the ClientID property provides the value for the HTML "id"attribute of the HTML tag of that server control. For examplethis:

<asp:Label ID="Label1"Text="Label" />

will render as this:

<spanid="Label1">Label</span>

That's why you often use the followingJavaScript statement to access the DOM element corresponding tosome ASP.NET server control:

var label =document.getElementByIdx("<%=Label1.ClientID%>");

which in turn renders as:

var label =document.getElementByIdx("Label1");

It is worth mentioning that the valuesof the ID, UniqueID and ClientID will be the same if the control isdefined in the master page (or the page). This however can oftenlead to unexpected errors. If the ID of the control is hardcodedinside the JavaScript statement (e.g. "Label1") this code will onlywork provided the control is defined in the Page or master page.Moving the control and the JavaScript code into a userc controlwith ID "UserControl1" will fail at runtime because the controlwill now render as:

<spanid="UserControl1_Label1">Label</span>

That's why you should prefer using the"<%= Label1.ClientID%>" syntax to getthe client-side id of server controls.

Additionaly the ClientID is used inASP.NET Ajax as the unique identifier of client-side controls. Thusthe following JavaScript statement is commonly used:

var control = $find("<%=MyControl1.ClientID %>");