试图在后面的代码中从ItemDataBound查找InsertItemTemplate内部的按钮

Question

I'm currently trying to find the insert button inside the InsertItemTemplate from the code behind. Essentially I'm trying to make this button's visibility false if the count reaches 10 or more. I keep getting the null reference exception error so I assume it's not finding the button. I've pasted code from the code behind file below:

protected void externalLinksList_ItemDataBound(object sender, ListViewItemEventArgs e)
{

        String connectionString = WebConfigurationManager.ConnectionStrings["UniString"].ConnectionString;
        SqlConnection myConnection = new SqlConnection(connectionString);

        myConnection.Open();

        String linkCountQuery = "SELECT COUNT(id) FROM links";

        SqlCommand linkCountQueryCommand = new SqlCommand(linkCountQuery, myConnection);
        Int32 linkCountQueryCommandValue = (Int32)linkCountQueryCommand.ExecuteScalar();

        if (linkCountQueryCommandValue >= 10)
        {
            Button InsertButton = (Button)e.Item.FindControl("InsertButton") as Button;
            InsertButton.Visible = false;
            Label linkLimit = (Label)e.Item.FindControl("linkLimit") as Label;
            linkLimit.Visible = true;
            linkLimit.Text = "Up to 10 external links are permitted. Please delete links before adding any more.";

        }
        else
        {
            Button InsertButton = (Button)e.Item.FindControl("InsertButton");
        }
    }

Answer 1

You're already executing a query once to generate the list of items to display and you're binding the ListView to that data source. At that point, you can inspect whatever that data source is to determine how many items it contains. I wouldn't repeat that query - going back to the database - for every single item displayed to get the same number again.

There are a few ways to do it. The easiest might be

• When you do your initial query to populate the ListView , get the count of items in that collection. (Do this wherever you're specifying the DataSource for the ListView .)
• Store it in a variable
• In externalLinksList_ItemDataBound check that variable - the original count of items in the list - and use that to determine whether to show or hide the button.

You could also just inspect the DataSource directly from externalLinksList_ItemDataBound . For example, if the data source is any sort of list you could do

var listView = (ListView)sender;
var dataSource = (IList)listView.DataSource;
if(dataSource.Count >= 10)
{
    //etc. 
}

There might be a more elegant solution that involves setting a property on the ListView itself to disable that button, but this would do it.