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Cell Blink for DataGridView

, 4 May 2008
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An article on adding a cell blink feature for DataGridView
Screenshot - DataGridViewCellBlink.jpg

Introduction

After reading many articles on The Code Project, I realized that it's my time to contribute. Few months ago, I came across a requirement for cells in a DataGridView control to blink when the cell value changed. The code presented here can be applied to any other grid.

The blinking of the grid cell is achieved in the following manner. When we update the value of a cell, we also change the background color of that cell to a blink color. To restore the cell background color to its original value, we run a background thread that iterates through a list of cells that are blinking and resets them to their original non blinking state.

The Code

The sample project has two functions. The first function DataInputThreadFunc() is used to generate random values to be filled / updated in the grid. The second function GridBlinkThreadFunc() is used to restore the cells to the non blink state.

Let's take a look at the first function DataInputThreadFunc():

private void DataInputThreadFunc()
{
    Random rand = new Random();
    while (true)
    {
        if (dataGridView1.IsDisposed)
            break;

        CellData data = new CellData();
        data.Row = rand.Next(0, 7);
        data.Col = rand.Next(0, 3);
        data.Time = DateTime.Now;

        int value = rand.Next(0, 101);

        dataGridView1.Invoke((MethodInvoker)delegate()
        {
            dataGridView1.Rows[data.Row].Cells[data.Col].Value = value;
            dataGridView1.Rows[data.Row].Cells[data.Col].Style
              .BackColor = Color.Salmon;
        });

        lock (_blinkData)
        {
            _blinkData.Add(data);
        }

        Thread.Sleep(1000);
    }
}

The function uses a while (true) loop as it's a background thread and will be shutdown automatically when the application is closed. if (dataGridView1.IsDisposed) check is done to make sure we do not call dataGridView1.Invoke() on a disposed object. This can happen when the user closes the application.

Next, we initialize an object of the class CellData to store the blink data:

class CellData
{
     public int Row;
     public int Col;
     public DateTime Time;
}

This class is used to store the row number, column number and the time when the value changed.

Next we use dataGridView1.Invoke() to make a call to the user interface thread and set the grid properties. We save the blink data in a generic list to be used later by the blink thread function. Since the list is altered by more than one thread, we synchronize access by locking the list on each access.

Now let's take a look at the blink thread function:

private void GridBlinkThreadFunc()
{
    while (true)
    {
        // Make a copy to avoid invalid operation exception
        // while iterating through the map
        List<CellData> tempBlinkData;
        lock (_blinkData)
        {
            tempBlinkData = new List<CellData>(_blinkData);
        }

        foreach (CellData data in tempBlinkData)
        {
            TimeSpan elapsed = DateTime.Now - data.Time;
            if (elapsed.TotalMilliseconds > 500) // 500 is the Blink delay
            {
                if (dataGridView1.IsDisposed)
                    return;

                dataGridView1.BeginInvoke((MethodInvoker)delegate()
                {
                    dataGridView1.Rows[data.Row].Cells[data.Col]
                      .Style.BackColor = dataGridView1.Columns[data.Col]
                      .DefaultCellStyle.BackColor;
                });

                lock (_blinkData)
                {
                    _blinkData.Remove(data);
                }
            }
        }

        Thread.Sleep(250); // Blink frequency
    }
}

At the very beginning, we make a copy of the _blinkData list. This helps us to modify the list while we iterate through the contents of the temporary copy. For each cell we find in the list, we check to make sure whether the blink time has elapsed or not. In this case, the blink time is 500 milliseconds. Any cell that has elapsed the blink time gets its background color reset to the default cell style background color and is removed from the list.

Again we make sure that we set the grid property only in the user interface thread. In addition, we lock the _blinkData list before altering it. Thread.Sleep(250) is the frequency with which we go through the list to turn off the cells. Ideally, it should be half the value of blink delay.

Points of Interest

You will notice that this code can be applied to any grid. This code can also be hidden in a class that extends a DataGridView control.

One thing I love about .NET 2.0 is dataGridView1.Invoke((MethodInvoker)delegate(). This statement lets you get away from writing a function and declaring a delegate.

A good point was made by "Kristof Verbiest" about the use of BeginInvoke() instead of Invoke(). The GridBlinkThreadFunc() uses BeginInvoke() to avoid unnecessary context switch.

History

  • 09/06/2007: First published
  • 09/11/2007: Changed the GridBlinkThreadFunc() to use BeginInvoke() instead of Invoke()
  • 05/02/2008: Edited the "Points of Interest" section

License

This article, along with any associated source code and files, is licensed under The zlib/libpng License

About the Author

Rammohan Raja
Architect
United States United States
Nothing to brag about, just another passionate software developer.
 
Work to make a living, don't live to work!
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Comments and Discussions

 
GeneralPerformance issue PinmemberHoa Le10-Nov-08 15:19 
GeneralRe: Performance issue PinmemberRaghavan Ram Raja14-Nov-08 3:21 
GeneralRe: Performance issue PinmemberHoa Le20-Nov-08 17:27 
GeneralVB.NET Version Here (Visual Studio 2005) Pinmembergratro14-Oct-08 2:26 
GeneralRe: VB.NET Version Here (Visual Studio 2005) PinmemberRaghavan Ram Raja14-Oct-08 3:07 
GeneralBlink PinmembertxALI29-Jan-08 4:16 
GeneralSome comments PinmemberKristof Verbiest10-Sep-07 20:16 
GeneralRe: Some comments PinmemberRam Mohan Raja11-Sep-07 4:42 
GeneralRe: Some comments PinmemberKristof Verbiest11-Sep-07 21:11 
GeneralRe: Some comments PinmemberRam Mohan Raja12-Sep-07 4:46 
GeneralRe: Some comments PinmemberKristof Verbiest12-Sep-07 21:06 
GeneralRe: Some comments PinmemberRam Mohan Raja13-Sep-07 4:05 
GeneralRe: Some comments PinmemberKristof Verbiest13-Sep-07 4:40 
GeneralRe: Some comments [modified] PinmemberRam Mohan Raja13-Sep-07 5:40 
1) All along I have tried to explain why I prefer using Invoke() over BeginInvoke() in the DataInputThreadFunc() function. First you say “the worker-thread running out of control: this is not likely to happen if the OS is performing a high priority operation, because both the GUI-thread AND the worker-thread will not be scheduled.” Then when I question that assumption you say “Of course there is no guarantee that the worker thread will not be scheduled, you could even give it a high priority to make sure it gets scheduled.” You still do not give up and say “But even then (in your example) this will only result in 1 GUI-message per second. This will not cause any problems for the GUI-thread (even if it is not scheduled for several seconds).”
I clearly tell you that “You have to realize that many people take the sample code presented in the article and use it directly. And many times more processing code (functionality) is added.”
Yes there is a specific problem blink a cell. It used mostly by financial application, this is also specific. Since you said “I cannot speak about these financial applications that you talk about.” Your opinion of this not being optimal solution is at best a guess as you are not aware of the use cases for the cell blink problem.
 
2) Using a timer is no less expensive than using a thread. And if you noticed I changed my article to use BeginInvoke() to minimize the thread switches. Trying to support your argument by ignoring valid points, that I agreed to and changed my code, shows signs of fatigue. When I tell you there is only one statement that is occasionally called in the GUI thread you come back and tell me all the other statements have very minimal processing again shows signs of exhaustion in your argument. Real world applications have more than one grid to blink and that too more than 10-20 times a second!
 
Please keep in mind this article tries to solve a real world problem and is not a lab experiment to demonstrate abstract theoretical concepts. My sample code is not just about how to blink cell but also how to use it in real world applications.

GeneralRe: Some comments Pinmemberradioman.lt@gmail.com31-Oct-07 0:26 
GeneralRe: Some comments PinmemberRam Mohan Raja31-Oct-07 3:33 

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