Check/Uncheck button check box

Question

In my program there is a button to mark and the same button to uncheck a checkbox.

Example: If I click once, it marks the check box, if I click again on the button it unchecks the check box. However, if you click again no longer mark the checkbox, after the second click the button loses the action.

Follows my code:

public frmLaudosPS()
{
    InitializeComponent();
    this.btn_seleciona.Click += this.marcar;
}

private void marcar(object sender, EventArgs e)
{
    DataTable table = (DataTable)dgw_laudos.DataSource;
    foreach (DataRow row in table.Rows)
        row["SELECIONAR"] = true;
    this.btn_seleciona.Click -= this.marcar;
    this.btn_seleciona.Click += this.desmarcar;
}

private void desmarcar(object sender, EventArgs e)
{
    DataTable table = (DataTable)dgw_laudos.DataSource;
    foreach (DataRow row in table.Rows)
        row["SELECIONAR"] = false;
}

Answer 1

Missing you remove and add the Handler in the uncheck event as well. Without this the code makes no sense.

private void desmarcar(object sender, EventArgs e)
{
    DataTable table = (DataTable)dgw_laudos.DataSource;
    foreach (DataRow row in table.Rows)
        row["SELECIONAR"] = false;

    this.btn_seleciona.Click -= this.desmarcar;
    this.btn_seleciona.Click += this.marcar;
}

Anyway, I think it would be much more interesting if you kept just one method. It makes no sense to keep the same code twice just to change the value of a boolean.

private void marcar_desmarcar(object sender, EventArgs e)
{
    DataTable table = (DataTable)dgw_laudos.DataSource;
    foreach (DataRow row in table.Rows)
        row["SELECIONAR"] = !Convert.ToBoolean(row["SELECIONAR"]);
}