将数据列表从gridview传输到另一页

Question

I have gridview look like this

Any time user click on Bookmark button, I wanna send the ProgramID of that row to the List and transfer it to another page by using Session.But my gridview transfer the all programID, even though that ID existed in the list. What am I doing wrong? This is the code for Bookmark button:

protected void btnSelect_Click(object sender, EventArgs e)
{


   Button b = (Button)sender;      
    GridViewRow row = (GridViewRow)b.NamingContainer;
    var ProgramID = row.FindControl("lblProgramID") as Label;
    string stringProgramID = ProgramID.Text;      
    List<string> bookmarkPrograms = (List<string>)Session["BookmarkProgram"];
    if (bookmarkPrograms == null)
        bookmarkPrograms = new List<string>();
    bookmarkPrograms.Add(stringProgramID);
    Session["BookmarkProgram"] = bookmarkPrograms;

}

And here is the code for the gridview in another page:

 protected void Page_Load(object sender, EventArgs e)
{
    List<string> bookMarkPrograms = (List<string>)Session["BookmarkProgram"];

    GridView1.DataSource = bookMarkPrograms;
    GridView1.DataBind();
}

Answer 1

Just want to post the whole solution for someone need it in the future:

 protected void btnBookmark_Click(object sender, EventArgs e)
{


    Button b = (Button)sender;      
    GridViewRow row = (GridViewRow)b.NamingContainer;
    var ProgramID = row.FindControl("lblProgramID") as Label;
    string stringProgramID = ProgramID.Text;      
    List<string> bookmarkPrograms = (List<string>)Session["BookmarkProgram"];
    if (bookmarkPrograms == null)
        bookmarkPrograms = new List<string>();


    if (bookmarkPrograms.Any(c => c.Equals(stringProgramID)))
    {
        FormMessage.Text = "You bookmarked this program already";
    }
    else
    {
        bookmarkPrograms.Add(stringProgramID);
    }
    Session["BookmarkProgram"] = bookmarkPrograms;




}

Answer 2

Not really sure about the flow of events. But if I get you correctly, you want the list to be constantly adding. You are doing

 Session["BookmarkProgram"] = bookmarkPrograms;

Which means that this variable is that specific value. But then if you do it again then this happens:

   List<string> bookmarkPrograms = new List<string>();

So you are erasing the old one. Make a method of getting the list so far, if is null or empty then create a new one. Otherwise don't or you'll empty what you have so far.

Update: You can try this:

List<string> bookmarkPrograms = (List<string>)Session["BookmarkProgram"] == null ? new List<string>():(List<string>)Session["BookmarkProgram"];

For checking if the value exists already then:

if (bookmarkPrograms.Any(c=>c.Equals(ProgramID)){//don't add}

The inside expression returns a boolean that is true when a value inside the list equals what you are comparing. This example asumes ProgramID is a string. As they are string you might want to add trim() and tolower() but doesn't seems like in this case a blank space might accidentally be added... or that casing might affect. Since this returns true for when it exists, add a ! in front of it so it adds to the list when it doesn't exists.