title: Check if a combobox value has been selected - C# .net
body: <p>I am trying to make my application better by handling exceptions. I have a form where if all the fields are not completed then show a message box to the user. Following is what I have attempted but even if all the fields are completed it still wont let me pass.</p>
  
  <pre><code>if (textBox1.Text == null || comboBox3.SelectedValue == null || 
      comboBox4.SelectedValue == null || 
      comboBox5.SelectedValue == null || comboBox8.SelectedValue == null)
  {
      MessageBox.Show("Please make sure you don't have any missing fields");
  }
  else
  {
      connection.Open();
  
      //update the settings to the database table 
      MySqlCommand command = connection.CreateCommand();
      // Insert into table_name values ("","name","1")
      command.CommandText = @"insert into CustomTests values ('','" + textBox1.Text + "'," + Convert.ToBoolean(checkBox1.CheckState) + ",'" + comboBox3.Text + "'," + comboBox4.Text + "," + comboBox5.Text + ",'" + comboBox8.Text + "'," + comboBox2.Text + "," + Timer_Enabled + ",'" + comboBox1.Text + "')";
  
      command.ExecuteNonQuery();
  }
  </code></pre>