David Truxall

List Databinding Performance With DisplayMembers and ValueMembers

My copy of MSDN magazine arrived last night, and I read the article Practical Tips For Boosting The Performance Of Windows Forms Apps. Good read. Anyway, I was shocked to find out that I have been databinding lists improperly ever since I have been using .Net. I frequently wrote my code like this:

//Bad Code
combobox.DataSource = datatable;
combobox.DisplayMember = "State";
combobox.ValueMember = "Id";

//Good Code
combobox.DisplayMember = "State";
combobox.ValueMember = "Id";
combobox.DataSource = datatable;

Apparenly, order matters very much. In the first example, the combobox binds using the DisplayMember, then rebinds when updated with the ValueMember. In the second example, the binding only happens once.

In our current app, we have two lists that contain thousands of items that need to be bound, so we are binding them during the startup process so the user won't wait when requesting that data. The startup time was reduced by just under 40% by changing the order of the code for binding.

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Generics and Enums or Enum.TryParse

I have a case where the user is entering strings into the application, and I have to match that string with the values from a given Enum. Normally that is not too difficult of a task, just convert the enum item to a string and compare, but in this instance I have a bunch of enums to do this with, so I didn't want to write a separate function for each enum type. So I figured generics might provide a solution and here is what I came up with, which is loosely based on the idea of int.TryParse:

/// <SUMMARY>
/// Takes a string that represents an enum member 
///   and returns the enum member
/// </SUMMARY>
/// <TYPEPARAM name="T">An Enum</TYPEPARAM>
/// <PARAM name="input">
///  The string that is the enum member name, case does 
///    not matter
/// </PARAM>
/// <PARAM name="returnValue">
/// The value from the enum that matches the string, or the 
/// first value of the enum /// </PARAM>
/// <RETURNS>
/// True when there is a match, false when not
/// </RETURNS>
/// <REMARKS>
/// - When no match the first item in the enum is returned
/// - The where clause attempts to constrain the input of T 
///   at compile time to be an Enum
/// </REMARKS>
private bool GetEnumValue<T>(string input, out T returnValue) 
             where T : struct, IComparable, IFormattable, IConvertible
{
    if(Enum.IsDefined(typeof(T), input))
    {
        returnValue = (T)Enum.Parse(typeof(T), input, true);
        return true;
    }
    else //input not found in the Enum, fill the out parameter
         //  with the first item from the enum
    {
        string[] values = Enum.GetNames(typeof(T));
        returnValue = (T)Enum.Parse(typeof(T), values[0], true);
        return false;
    }
}

Awesome IIS Resource

Comboboxes and Double-Clicks

The standard combobox control doesn't support the double-click event, as it is actually a combination of more than one control itself. In my case, I am using the combobox in simple mode with a textbox at the top and a permanently open list directly below the textbox. I needed for the listbox below to respond to the user double-clicking a list item. I found a great solution in a Usenet post by Jacques Bourgeois in microsoft.public.dotnet.framework.windowsforms.controls. Essentially the code simulates a double-click using the single-click event and a timer control.

Declare a timer control in your class, and in the load event of the form instantiate the timer set the interval of the timer to the interval of the double-click as set in the user's system:

In the event handler for the timer, set the code to stop the timer:

Add code to the single-click event handler to handle the double-click. When the event handler fires, if the timer is not enabled, start the timer (the first click). If the timer is enabled, a previous click has occurred within the system set interval for a double-click. This must be the second click of the double-click, so do whatever you needed the double-click to do and then disable the timer for the next single-click event.