Datagridview becomes empty once its datasource data is changed

Question

Datagridview becomes empty once its datasource data is changed

Pengfei Liu 21

Hi,

My Winform application has a datagridview dgvTag and a button btnGen in a User Control. Clicking the button will generate the data in a datatable dtTag which is set as the data source of the datagridview. The code is like this:

        private void btnGen_Click(object sender, EventArgs e)
        {
            dtTag.Reset();
            dtTag.Columns.Add("A", typeof(string));
            dtTag.Columns.Add("B", typeof(string));
            dtTag.Columns.Add("C", typeof(string));
            dtTag.Columns.Add("D", typeof(string));
            dtTag.Columns.Add("E", typeof(string));
            dtTag.Columns.Add("F", typeof(string));
            dtTag.Columns.Add("G", typeof(string));
//put the code here to generate the tags
dgvTag.DataSource = dtTag;
            MessageBox.Show("Database generated.", "Info", MessageBoxButtons.OK, MessageBoxIcon.Information);

        }

Somehow, this code only works for the first time. If the button was clicked for the 2nd time, the datagridview becomes empty while only column headers are still there. I am sure the datatable dtTag is not not empty. Could you please help on this? Thanks.

Viorel 122.6K Reputation points

2021-06-23T04:14:21.987+00:00

Does your code insert rows? Then check if this sequence helps (instead of line 12): dgvTag.DataSource = null; dgvTag.DataSource = dtTag.
Pengfei Liu 21 Reputation points

2021-06-23T13:54:01.097+00:00

Hi Viorel-1,

Yes. The code add new row like this:

dtTag.Rows.Add(new object[] { "TYPE", "SCOPE", "NAME", "DESCRIPTION", "DATATYPE", "SPECIFIER", "ATTRIBUTES" });

I tried your code. But got the same result, meaning the 1st click will populate the data in the datagridview and the 2nd click will clear the data.

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Viorel 122.6K Reputation points

2021-06-23T04:14:21.987+00:00

Does your code insert rows? Then check if this sequence helps (instead of line 12): dgvTag.DataSource = null; dgvTag.DataSource = dtTag.
Pengfei Liu 21 Reputation points

2021-06-23T13:54:01.097+00:00

Hi Viorel-1,

Yes. The code add new row like this:

dtTag.Rows.Add(new object[] { "TYPE", "SCOPE", "NAME", "DESCRIPTION", "DATATYPE", "SPECIFIER", "ATTRIBUTES" });

I tried your code. But got the same result, meaning the 1st click will populate the data in the datagridview and the 2nd click will clear the data.

Answer 1

Viorel 122.6K

The next sequence seems to work:

dtTag.Clear( );
dtTag.Columns.Clear( );

Use it instead of dtTag.Reset( ), which appears to cause issues.

Pengfei Liu 21 Reputation points

2021-06-23T21:58:42.803+00:00

Thank you, Viorel. The code works like charm.

Answer 2

Hi PengfeiLiu-9437,
I made a test with your code and it worked fine.
Please refer to the following code:

private void button1_Click(object sender, EventArgs e)  
{  
    DataTable dtTag = new DataTable();  
    dtTag.Reset();  
    dtTag.Columns.Add("A", typeof(string));  
    dtTag.Columns.Add("B", typeof(string));  
    dtTag.Columns.Add("C", typeof(string));  
    dtTag.Columns.Add("D", typeof(string));  
    dtTag.Columns.Add("E", typeof(string));  
    dtTag.Columns.Add("F", typeof(string));  
    dtTag.Columns.Add("G", typeof(string));  
    //put the code here to generate the tags  
    String connectionString = "your connectionString";  
  
    // Create a new data adapter based on the specified query.  
    SqlDataAdapter dataAdapter = new SqlDataAdapter("select * from test", connectionString);  
  
    // Create a command builder to generate SQL update, insert, and  
    // delete commands based on selectCommand.  
    SqlCommandBuilder commandBuilder = new SqlCommandBuilder(dataAdapter);  
  
    // Populate a new data table and bind it to the BindingSource.                  
    dataAdapter.Fill(dtTag);         
    dgvTag.DataSource = dtTag;  
    MessageBox.Show("Database generated.", "Info", MessageBoxButtons.OK, MessageBoxIcon.Information);  
}

Best Regards,
Daniel Zhang

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Pengfei Liu 21 Reputation points

2021-06-23T15:11:26.903+00:00

Hi Daniel,

What should I put here to replace "your connectionString"? I have no idea on how to use SQL.

I guess the "test" in ""select * from test"" also to be replaced by something else. What is it?

Thanks.

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Datagridview becomes empty once its datasource data is changed

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