About GridView With CheckBox Column

I want validate if CheckBox has checked at GridView through JavaScript,if true then return text to Code behind.
我想用 JavaScript 確認 GridView 裡面的 CheckBox 是否有勾選資料，若有、回傳文字到Code behind.

1.在 aspx 網頁裡面放入隱藏控制項：

<asp:HiddenField ID="HDNValue" Value="0" runat="server" />

2.在 aspx 網頁裡面的 Button1 呼叫 JavaScript

<asp:Button ID="Button1" runat="server" onclick="Button1_Click" Text="選取" OnClientClick="returnString()"/>

3.JavaScript程式碼：

function returnString() 

{
    debugger;
    document.getElementById("HDNValue").value = "Return Text";
}

4.Button1的Click事件加入：

string sIsCheckData = HDNValue.Value;
if (sIsCheckData == "True")
{

....do something...

}