Devexpress XtraGrid CustomDrawCell: Repaint of Cell Only on Mouse Over/Clicking on Form Elements

Welcome to this comprehensive guide on using Devexpress XtraGrid’s CustomDrawCell event to repaint cells only when the mouse is hovered over or when certain form elements are clicked. This article will walk you through the process of creating a dynamic and interactive grid that responds to user interactions.

What is CustomDrawCell?

The CustomDrawCell event is a powerful feature in Devexpress XtraGrid that allows you to customize the appearance of individual cells in the grid. It provides a way to access the underlying graphics object, enabling you to draw custom content, such as images, shapes, and text, directly onto the cell.

Why Use CustomDrawCell?

Using CustomDrawCell can enhance the user experience of your grid-based application by:

• Adding visual cues to highlight important data
• Implementing custom editors and validators
• Creating interactive elements, such as buttons and links
• Improving performance by reducing unnecessary drawing operations

Repainting Cells on Mouse Over

To repaint cells only when the mouse is hovered over, we’ll use the CustomDrawCell event in combination with the MouseMove event. We’ll create a simple example that changes the cell’s background color when the mouse is hovered over.

private void gridView1_CustomDrawCell(object sender, CustomDrawCellEventArgs e) {
  if (e.RowHandle >= 0) {
    GridView view = sender as GridView;
    GridColumn column = view.Columns[e.Column];
    Rectangle cellRect = view.GetCellDisplayRectangle(e.Column, e.RowHandle, true);

    // Clear the cell's background
    e.Cache.FillRectangle(e.Cache.GetSolidBrush(Color.White), cellRect);

    // Check if the mouse is hovered over the cell
    if (view.IsMouseOverCell(e.RowHandle, e.Column)) {
      // Change the cell's background color to yellow
      e.Cache.FillRectangle(e.Cache.GetSolidBrush(Color.Yellow), cellRect);
    }

    // Draw the cell's text
    e.Cache.DrawString(e.CellValue.ToString(), e.Appearance.Font, e.Cache.GetSolidBrush(e.Appearance.GetForeColor()), cellRect);
  }
  e.Handled = true;
}

In this example, we first clear the cell’s background and then check if the mouse is hovered over the cell using the IsMouseOverCell method. If the mouse is hovered over, we change the cell’s background color to yellow. Finally, we draw the cell’s text using the DrawString method.

Repainting Cells on Clicking Form Elements

To repaint cells when certain form elements are clicked, we’ll use the CustomDrawCell event in combination with the Click event of the form elements. We’ll create an example that changes the cell’s background color when a button is clicked.

private void gridView1_CustomDrawCell(object sender, CustomDrawCellEventArgs e) {
  if (e.RowHandle >= 0) {
    GridView view = sender as GridView;
    GridColumn column = view.Columns[e.Column];
    Rectangle cellRect = view.GetCellDisplayRectangle(e.Column, e.RowHandle, true);

    // Clear the cell's background
    e.Cache.FillRectangle(e.Cache.GetSolidBrush(Color.White), cellRect);

    // Check if the button is clicked
    if (button1Clicked) {
      // Change the cell's background color to blue
      e.Cache.FillRectangle(e.Cache.GetSolidBrush(Color.Blue), cellRect);
    }

    // Draw the cell's text
    e.Cache.DrawString(e.CellValue.ToString(), e.Appearance.Font, e.Cache.GetSolidBrush(e.Appearance.GetForeColor()), cellRect);
  }
  e.Handled = true;
}

private bool button1Clicked = false;

private void button1_Click(object sender, EventArgs e) {
  button1Clicked = true;
  gridView1.Invalidate();
}

In this example, we use a boolean variable button1Clicked to track the state of the button. When the button is clicked, we set the variable to true and invalidate the grid using the Invalidate method. In the CustomDrawCell event, we check the state of the variable and change the cell’s background color to blue if the button is clicked.

Optimizing Performance

When using CustomDrawCell, it’s essential to optimize performance by minimizing unnecessary drawing operations. Here are some tips to help you optimize performance:

• Use the Invalidate method to invalidate only the cells that need to be redrawn
• Use the BeginUpdate and EndUpdate methods to batch updates and reduce the number of redraws
• Use the CustomDrawCellEventArgs.Cache property to reuse graphics objects and reduce memory allocation
• Avoid using complex graphics operations, such as anti-aliasing and gradients, in high-traffic areas of the grid

Best Practices

Here are some best practices to keep in mind when using CustomDrawCell:

• Keep the CustomDrawCell event handler short and concise to improve performance
• Use the e.Handled property to indicate that the event has been handled and processed
• Avoid using the CustomDrawCell event to perform complex calculations or database queries
• Test your implementation thoroughly to ensure it works as expected in different scenarios and environments

Conclusion

In this article, we’ve explored the power of Devexpress XtraGrid’s CustomDrawCell event and how it can be used to repaint cells only on mouse over or when certain form elements are clicked. By following the examples and best practices outlined in this article, you can create dynamic and interactive grids that enhance the user experience of your application.

Keyword	Description
Devexpress XtraGrid	A powerful grid control for WinForms applications
CustomDrawCell	An event that allows custom drawing of individual cells in the grid
MouseMove	An event that occurs when the mouse is moved over the grid
Click	An event that occurs when a form element, such as a button, is clicked

We hope you found this article informative and helpful. If you have any questions or comments, please don’t hesitate to ask.

Happy coding!

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