get actual column width

Question

I am building a DataGridView table programmatically and placing it within a GroupBox on a form.

I insert the data, then resize the columns automatically to fit the data. I then want to resize the groupbox to the size of the DataGridView. For each column and row, I get their respective width and height, which technically should be accurate, and update the panel and overall DataGridView sizes.

The problem is that Column.Width always returns 100 pixels regardless of its actual size (see screenshot: actual column width is around 30px, not 100). If I manually enter width = 90 pixels, the resizing is quite accurate!

matrix = new DataGridView();
//modify behaviour
matrix.ColumnHeadersVisible = false;
matrix.AllowUserToResizeColumns = false;
matrix.AutoSizeColumnsMode = DataGridViewAutoSizeColumnsMode.AllCells;
matrix.RowHeadersVisible = false;
matrix.AllowUserToResizeRows = false;
//modify positioning
matrix.Location = new Point(10, 20);
//matrix.Anchor = (AnchorStyles)(AnchorStyles.Left | AnchorStyles.Top | AnchorStyles.Bottom | AnchorStyles.Right);
matrix.Dock = DockStyle.Fill;
//set the size of the matrix
matrix.ColumnCount = col;
matrix.RowCount = row;


//Data now inserted...
matrix.AutoResizeColumns(); //correctly resizes the columns

int height = 0;
foreach (DataGridViewRow row in matrix.Rows)
{
    height += row.Height;
}
height += matrix.ColumnHeadersHeight;

int width = 0;
foreach (DataGridViewColumn col in matrix.Columns)
{
    width += col.Width;
    //PROBLEM: Width always  = 100 pixels.
}
width += matrix.RowHeadersWidth;
//width = 90; //override width manually
matrix.Size = new Size(width + 2, height + 2);
panel.Size = new Size(matrix.Width, matrix.Height);

the panel is so large because width isn't 90px but 357 roughly, which is wrong!

EDIT: PARTIAL FIX I have found a way to get the correct width of a cell:

DataGridView.Rows[0].Cells[0].ContentBounds.Width
//ContentBounds = a rectangle with the exact dimensions of that cell

I can now set the DataGridView the correct size, but only if it's not Docked to Fill. Setting matrix.Dock = DockStyle.Fill prevents the resizing to occur correctly.

Answer 1

I guess that is because you're autosizing your columns in row:

matrix.AutoSizeColumnsMode = DataGridViewAutoSizeColumnsMode.AllCells;

try to change it to:

matrix.AutoSizeColumnsMode = DataGridViewAutoSizeColumnsMode.None;

Answer 2

I have figured out what the problem is:

1. DataGridView.Dock = DockStyle.Fill prevented the DataGridView.AutoResizeColumns() method from doing anything.

2. Rectangle rect = matrix.Rows[0].Cells[0].ContentBounds getting the dimensions of the rectangle containing the cell values didn't update after AutoResizeColumns()

3. I tried setting the columns manually, but as heq suggested, the AutoSizeColumnsMode must be set to None in order to be able to modify the width.

4. I adjusted the width of each column manually, to be 10px for each character inside the cell

Final Solution

/* Create the DataGridView */
matrix = new DataGridView();
//modify behaviour
matrix.ColumnHeadersVisible = false;
// matrix.columnhea
matrix.AllowUserToResizeColumns = false;
matrix.AutoSizeColumnsMode = DataGridViewAutoSizeColumnsMode.None;
matrix.RowHeadersVisible = false;
matrix.AllowUserToResizeRows = false;
matrix.ReadOnly = true;
//modify positioning
matrix.Location = new Point(10, 20);
//matrix.Dock = DockStyle.Fill;
matrix.Anchor = (AnchorStyles)(AnchorStyles.Left | AnchorStyles.Top | AnchorStyles.Bottom | AnchorStyles.Right);
//set the size of the matrix
matrix.ColumnCount = cols;
matrix.RowCount = rows;

panel.Controls.Add(matrix);

/* Set the data contents (not shown) */
...

/* Adjust the width of columns */
int width = 0;
int height = 0;

for(int c = 0; c < cols; c++) 
{
  int largest = 0; //largest number of characters in cell
  for(int r = 0; r < rows; r++) 
  {
      int len = matrix.Rows[r].Cells[c].Value.ToString().Length;
      if (len > largest)
      {
          largest = len;
      }
  }
  matrix.Columns[c].Width = largest * 10;
  width += largest * 10;
}

/* Get height of table */
foreach (DataGridViewRow row in matrix.Rows)
{
    height += row.Height;
}

/* Set the DataGridView Size and Parent Panel size */
//Note: first set the parent panel width, the table is anchored to all of its edges
// as such table wont resize correctly if the panel isn't up to size first
panel.Size = new Size(width + 20, height + 30);
matrix.Size = new Size(width + 3, height + 3); //is it 1px per row and col?

/* Parent Panel settings kept to default, no modifications */