I need help calling a cell value from a datagridview - I keep getting an out of index range exception

Question

So.... I have created a new project, I have added a database and dataset, created a table, populated it, set it as a data source, and finally have pulled a 'details' and 'datagridview' onto my form.

I have tested these and all displays just fine.

Now the problem. I want to call a cell value and then carry out a task based on the result, but everytime I try, I get an out of range exception.

I've looked around at other topics and tutorials and similar questions and it suggests that I'm trying to call a cell that doesnt exist. This doesnt make sense, as I've tried various low-number index combinations, and my table consists of 4 columns and 16 rows, all of which contain data.

All other indicators point to the program not understanding that the datagridview actually contains data - as if it wants to me to define it before it can call the data - but this makes no sense to me because I've pulled it from a database and I can view the data with no problems when I run the program.

I've tried various different codes to call on a cell, but I get the same exception every time.

int testValue1 = (int)islandMapDataGridView[1, 1].Value;
Console.WriteLine(testValue1);

I should point out that I'm reasonably new to this. What am I doing wrong?

EDIT - Thank you for pointing me to a similar question with a lengthy answer - unfortunately I've looked at many just like this already. They are suggesting that I'm picking a cell that does not exist.

I am aware that these indexes start at 0 and I should compensate for this. Again, my datagridview has 4 columns and 16 rows. I am (for example) attempting to get the data at cell index 1,1 - which is well within the range of the datagridview.

The problem does not seem to be that I am calling a cell that falls outside the range of cells and rows in the datagridview but rather that it seems to think that nothing is there at all. But if I disable the line of code that is supposed to return the value - when I run the program I can see the table just fine and the data is there.

If I have to take the time to define the datagridview just so I can call a value from a cell, then what was the point in setting up databases, datasets, datasources and tables in the first place?

2nd EDIT - What do I have to do to get this looked at again????? Somebody has stated this is an exact duplicate of another question, and linked me to it. It is NOT an exact duplicate. I am NOT trying to reference a cell that falls outside of the datagridview. The problem seems to be that the datagridview is not properly reporting back the data contained within in. Presumably I have missed some sort of initialisation, or there is something wrong with the binding.... I dont know... If I knew, then it wouldnt be a problem. The linked topic/question does nothing to explain what I am missing. Please can I get some help with this? Please?

3rd Edit - I'd like to add that since my opening question, I've been looking around and trying to find a solution - I stumbled across a tutorial carrying out a similar exericse, and they included the following line of code:

islandMapDataGridView.SelectionMode = DataGridViewSelectionMode.CellSelect;

I hoped this might resolve my problem, but sadly it did not.

I am guessing that something fundamental is missing that allows me to report values from the datagrid, or it is somehow not properly loaded or configured.

I would appreciate any help - even if just to point me a tutorial or similar which expains how to set this sort of thing up.

Do I need to set up a class in order to fetch a value from a cell? Do I need to set up a database context? Please, what am I missing here?

4th Edit! - Ok so here is the code that was automatically generated by the program when i dragged in the 'datagridview' and 'details' from the table in datasources.

private void islandMapBindingNavigatorSaveItem_Click(object sender, EventArgs e)
    {
        this.Validate();
        this.islandMapBindingSource.EndEdit();
        this.tableAdapterManager.UpdateAll(this.starterIslandDataSet);
    }

    private void Form4_Load(object sender, EventArgs e)
    {
        // TODO: This line of code loads data into the 'starterIslandDataSet.IslandMap' table. You can move, or remove it, as needed.
        this.islandMapTableAdapter.Fill(this.starterIslandDataSet.IslandMap);
    }

There doesnt appear to be anything specifically here for the datagridview - but again, when i run the program, it displays it just fine, including all the information that i entered into the table.

Here is the code I am trying to use to pull info from the database -

private void MapTilesTest()
    {
        islandMapDataGridView.SelectionMode = DataGridViewSelectionMode.CellSelect;

        foreach (Control control in tableLayoutPanel2.Controls)


            {
            PictureBox maptile = control as PictureBox;
            if (maptile != null)

            {
                int testValue1 = (int)islandMapDataGridView[1, 1].Value;
                Console.WriteLine(testValue1);

            }

        }

I am using console.writeline just to confirm that i can indeed pull a value from the table.

I have looked at tutorials for advice, and i see lots where they are manually coding the datagridview and manually inputting the data into the datagridview in the code - i assume this is one way of doing it - but i cant find a good example where someone is pulling information from a database in the same way.

Answer 1

After reading the comments, it may be helpful to clarify some major points in what you are trying to accomplish. First is the reality that when you try to access a cell’s value in a grid, it is imperative that you check several possibilities.

First, does the cell actually exist? In your posted example, you are trying to access the value from the cell at row 1 column 1. This can be accomplished by simply checking to make sure the grid has at least two (2) rows and at least two (2) columns. If you do not check this, and the grid has less than two (2) rows or less than two (2) columns… your code will crash and burn. This obviously is a bad thing and “you” as a programmer should ALWAYS assume the possibility that the cell you are looking for does not exist, is null or the cells value is not a number.

If you have not done so yet, I recommend you take a look at the Try/Catch construct. This useful construct will allow you to TRY some part of your code and CATCH any errors… like an index out of range error. The try catch construct is useful to catch errors and respond to them. In your posted code there would be three possible errors in the line int testValue1 = (int)islandMapDataGridView[1, 1].Value; And you would want to catch all these possible errors in the following order.

1) The cell at row 1 column 1 does not exist.

2) The cells “Value” at column 1 row 1 is null.

3) The cells “Value” at column 1 row 1 is not a number.

The line int testValue1 = (int)islandMapDataGridView[1, 1].Value; could produce one of the three errors above. If the cell does not exist, is null or is not a number, then there would be no value to output.

The convenient aspect of the Try/Catch is that you can “catch” all errors or specific errors. Example, the code below will catch all three possible errors.

private void MapTilesTest() {
  try {
    int testValue1 = (int)islandMapDataGridView[1, 1].Value;
    MessageBox.Show("Value is: " + testValue1.ToString());
  }
  catch (ArgumentOutOfRangeException ex) {
    MessageBox.Show("Cell 1,1 does not exist: total rows = " + islandMapDataGridView.Rows.Count + " total colums = " + islandMapDataGridView.Columns.Count);
  }
  catch (NullReferenceException ex) {
    MessageBox.Show("The 'Value' at Cell 1,1 is null (most likely the new row): total rows = " + islandMapDataGridView.Rows.Count + " total colums = " + islandMapDataGridView.Columns.Count);
  }
  catch (InvalidCastException ex) {
    MessageBox.Show("The 'Value' at Cell 1,1 is NOT a number or is an empty cell: actual cell value is: " + islandMapDataGridView[1, 1].Value.ToString());
  }
  catch (Exception ex) {
    MessageBox.Show("Some other error: " + ex.GetBaseException());
  }
}

A second approach is to manually check for these errors. The code below demonstrates this and also uses an int.TryParse construct to validate if the value in the cell is actually a number. Using a TryParse is a better way to convert strings to numbers and validate the string is actually a number. Casting a string to an int as your code does, ALWAYS has the possibility of failure and should ALWAYS be checked. The Try/Parse construct helps in this checking.

The code below still uses a Try/Catch however the difference is that the code below is manually checking for the specific errors: index out of range, a null cell value and valid integer string values. These error checks are made BEFORE they happen and therefore the exceptions will not be thrown. If there are ANY other exceptions thrown… the catch clause will get them.

private void MapTilesTest() {
  try {
    // make sure there are enough rows
    if (islandMapDataGridView.Rows.Count < 2) {
      MessageBox.Show("Row Index is out of range: total rows = " + islandMapDataGridView.Rows.Count);
      return;
    }
    // make sure ther are enough columns
    if (islandMapDataGridView.Columns.Count < 2) {
      MessageBox.Show("Column Index is out of range: total columns = " + islandMapDataGridView.Columns.Count);
      return;
    }
    // make sure the cells value is not null
    if (islandMapDataGridView[1, 1].Value == null) {
      MessageBox.Show("Value is null (most likely the new row)");
      return;
    }
    // Make sure the cells value is actually an integer
    int testValue1 = 0;
    if (int.TryParse(islandMapDataGridView[1, 1].Value.ToString(), out testValue1)) {
      MessageBox.Show("Valid Value is: " + testValue1.ToString());
    }
    else { 
      MessageBox.Show("Value is not a number: " + islandMapDataGridView[1, 1].Value.ToString());
    }
  }
  catch (Exception ex) {
    MessageBox.Show("Error: " + ex.Message);
  }
}

I hope this makes sense. Lastly, I can assure you that the error you are getting is coming from when the data is being filled into the grid. Obviously, when the first row is filled with data, your code will crash without these checks and this is exactly what is happening. When I asked you to show where the line is being called and you responded with it is being called in the method MapTilesTest, does not help. We need to know WHEN is the MapTilesTest method called in relation to when the grid is filled. I can only assume that MapTilesTest is getting called (before or during) when the grid is filled with data and therefore will cause the error you describe as soon as the first row is added to the grid.