Why in winforms, after form resize does 'screen.getworkingarea( this) .height' return the same value

Question

Attempting to draw a grid on a winforms form. Draws ok. If I resize the form at all the screen.getworkingarea returns the original values and redraws the grid to the same size with the resized section blank. Having stepped through the code I can see that the screen working area for (this) the form remains the same though the form is now larger.

As can be seen from the code I have tried to isolate the problem but can see no reason for it, other than (this) in the screen.getworkingarea. Is there a way to tell the form that it has a new working area? I have yet to find it.

private void DrawGrid(Boolean Resize)

{

 int NumOfYLines;

 int NumOfXLines;

 int GridHeight;

 int GridWidth;

 Pen ThisPen = new Pen(Color.LightSlateGray, 1);

 if (!Resize)

 {

     GridHeight = this.Height;

     GridWidth = this.Width;

 }

 else

 {

     GridHeight = Screen.GetWorkingArea(this).Height;

     GridWidth = Screen.GetWorkingArea(this).Width;

     ThisPen = new Pen(Color.DarkRed, 2);

//the pen color change was to check for the redraw being over the same lines

 }

 NumOfYLines = GridHeight / GridSize;

 NumOfXLines = GridWidth / GridSize;

 int x1; int y1; int x2; int y2;

 for (int y = 0; y < NumOfYLines; ++y)

 {

     x1 = 0; y1 = y * GridSize; x2 = NumOfYLines * GridSize; y2 = y * GridSize;

     Misc.writeLog("added in DrawGrid Y lines:" + x1.ToString() + " " + y1.ToString() + " " + x2.ToString() + " " + y2.ToString() + " " + Resize.ToString(), true);

     TheseGraphics.DrawLine(ThisPen, 0, y * GridSize, GridWidth, y * GridSize);

 }

 for (int x = 0; x < NumOfXLines; ++x)

 {

     x1 = x * GridSize; y1 = 0; x2 = x * GridSize; y2 = NumOfXLines * GridSize;

     Misc.writeLog("added in DrawGrid X lines:" + x1.ToString() + " " + y1.ToString() + " " + x2.ToString() + " " + y2.ToString() + " " + Resize.ToString(), true);

     TheseGraphics.DrawLine(ThisPen, x * GridSize, 0, x * GridSize, NumOfXLines * GridSize);

 }

}

Answer 1

If the screen has not been resized, but the form has been, then try to use the this.ClientSize.Width and this.ClientSize.Height.

Answer 2

Hi @Peter Reilly , Welcome to Microsoft Q&A,

This.ClientSize returns the size of the form's client area, not including borders or title bars, which is ideal for dynamically adjusting the grid drawing range. When resizing, you can tell the form to redraw the entire client area by calling Invalidate. By using the Graphics object (e.Graphics) provided by PaintEventArgs, you can ensure that the drawing area is correct and avoid potential problems.

using System;
using System.Drawing;
using System.Windows.Forms;

namespace xxx
{
    public partial class Form1 : Form
    {
        private int GridSize = 20; // Set the size of the grid cell
        public Form1()
        {
            InitializeComponent();
            // Initialize the form
            this.Text = "Grid drawing example";
            this.BackColor = Color.White;
            this.Size = new Size(800, 600);

            // Register Paint and Resize events
            this.Paint += MainForm_Paint;
            this.Resize += MainForm_Resize;
        }
        // Triggered when redrawing
        private void MainForm_Paint(object sender, PaintEventArgs e)
        {
            DrawGrid(e.Graphics, false);
        }

        // Triggered when resizing the window
        private void MainForm_Resize(object sender, EventArgs e)
        {
            this.Invalidate(); // Notify the form that it needs to be redrawn
        }

        // Method for drawing the grid
        private void DrawGrid(Graphics g, bool resize)
        {
            int numOfYLines;
            int numOfXLines;
            int gridHeight;
            int gridWidth;

            Pen thisPen = new Pen(Color.LightSlateGray, 1);

            if (resize)
            {
                gridHeight = this.ClientSize.Height; // Use the height of the client area of ​​the form
                gridWidth = this.ClientSize.Width; // Use the width of the client area of ​​the form
                thisPen = new Pen(Color.DarkRed, 2); // Mark the grid when resizing with red lines
            }
            else
            {
                gridHeight = this.ClientSize.Height;
                gridWidth = this.ClientSize.Width;
            }

            numOfYLines = gridHeight / GridSize; // Calculate the number of vertical lines
            numOfXLines = gridWidth / GridSize; // Calculate the number of horizontal lines

            // Draw horizontal lines
            for (int y = 0; y <= numOfYLines; ++y)
            {
                int yPos = y * GridSize;
                g.DrawLine(thisPen, 0, yPos, gridWidth, yPos);
            }

            // Draw vertical lines
            for (int x = 0; x <= numOfXLines; ++x)
            {
                int xPos = x * GridSize;
                g.DrawLine(thisPen, xPos, 0, xPos, gridHeight);
            }
        }

    }
}

Best Regards,

Jiale

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