Asp.net WebForms DropDownList-具有不同值和显示文本的控件（DataValueField / DataTextField）

Question

I have two entity classes - Users and Tasks. Every User has the following properties: UserId (int), Username (string), Password (string), FirstName (string), Lastname (string)

and every Task, these: TaskId (int), Title (string), Description (string), EstimatedTime (int), CreatedOn (Datetime), CreatedBy (int), AssignedTo (int), Finished (bool)

So CreatedBy and AssignedTo are actually UserIds - CreatedBy is the Id of the user, who created the task, and AssignedTo - the id of the one the task is for. I have a database where I use them - no problems there.

In my WebForms Application I use a GridView to show the Tasks. So I hide the TaskId and all the other properties are shown as columns in the GridView. But, the problem is, I don't want my users to see the values in CreatedBy and AssignedTo as ids(integers) - I want them to see the values as Usernames, so it would look like this: AssignedTo - "myUsername", and not like this: AssignedTo - 321.

This is my first problem, I don't know how to do that. As you will see in my code, the ItemTemplate is a Label, Bound to the property AssignedTo. How can I keep the value invisible and display the username instead?

Second, as I log in as an admin, I want to be able to edit the Tasks. So I added these command fields to my GridView:

<asp:CommandField ShowEditButton="true" />
<asp:CommandField ShowDeleteButton="true" />

I have a TaskRepository ans UserRepository that I use to access my database. For example, the GridView is bound to a property in my TaskRepository that returns a list of all the tasks :

TaskRepository taskRepo = new TaskRepository;
GridViewTasks.DataSource = taskRepo.GetAll();
GridViewTasks.DataBind();

Everything works perfectly. And here is my AssignedTo ItemTemplate:

<asp:TemplateField HeaderText="Assigned to">
   <EditItemTemplate>
                    <asp:DropDownList ID="editAssignedTo" runat="server" DataTextField="Username" DataValueField="UserId"></asp:DropDownList>
   </EditItemTemplate>
   <ItemTemplate>
                    <asp:Label ID="lbAssignedTo" runat="server" Text='<%#Bind("AssignedTo")%>'></asp:Label>
   </ItemTemplate>
</asp:TemplateField>

So when I edit a task, I click "Edit" and I can change the values in the selected row in each column. But the problem, again, is with AssignedTo. As you can see from the code, when I edit it I see a DropDownList where insted of Ids, I have to choose from usernames. But the moment I try to save my changes, I get an object null reference exception.. I don't know why. Here is my code:

protected void GridViewTasks_RowUpdating(object sender, GridViewUpdateEventArgs e)
        {
            GridViewRow selectedRow = GridViewTasks.Rows[e.RowIndex];
            Tasks task = new Tasks();
            task.TaskId = (int)GridViewTasks.DataKeys[e.RowIndex].Value;
            TextBox title = (TextBox)selectedRow.FindControl("tbTitle");
            task.Title = title.Text;
            TextBox description = (TextBox)selectedRow.FindControl("tbDescription");
            task.Description = description.Text;
            Label createdOn = (Label)selectedRow.FindControl("lblCreatedOn");
            task.CreatedOn = DateTime.Parse(createdOn.Text);
            Label createdBy = (Label)selectedRow.FindControl("lblCreatedBy");
            task.CreatedBy = int.Parse(createdBy.Text);
            TextBox estimTime = (TextBox)selectedRow.FindControl("tbEstimTime");
            task.EstimatedTime = int.Parse(estimTime.Text);          
            DropDownList assignedTo = (DropDownList)selectedRow.FindControl("editAssignedTo");           
            task.AssignedTo = int.Parse(assignedTo.SelectedItem.Value);
            Label lblFinished = (Label)selectedRow.FindControl("lblFinished");
            task.Finished = bool.Parse(lblFinished.Text);
            taskRepo.Save(task);
            BindDataToGridView();
        }

Everything works with the other controls but when it gets to task.AssignedTo, I get the exception. Here is what I want to happen: When I click Edit, I want to see a DropDownList in the AssignedTo column with all my users usernames to choose from (so far, so good) and when I select a user and click Update, I want it to get the selected username value of assignedTo, knowing the userId it corresponds to and update my Task. Where do I go wrong?

Sorry for the long post, I tried to be as thorough as possible and since I don't understand where the problem is, maybe I even missed something important (this is my first post). Please help, because I've been stuck on this since forever.

Answer 1

For you first problem you can use an OnRowDataBound method to convert your ID to a username. Essentially you get the ID from the row and get the name based on the ID.

For example:

protected void Gridview_RowDataBound(object sender, GridViewRowEventArgs e)
{
    if(e.Row.RowType == DataControlRowType.DataRow)
    {
       //get your control like in rowupdating
       //take the ID value and query against your user info to get the name
       // set the value
    }
}

For your second problem it might be that you need OnRowUpdated instead. I don't have VS installed on this computer to try it out, so this is just a guess.