Can't leave a bound combobox after deleting its content

For the first item, the best solution is to add another item to the DataTable that maps "" to DBNull.Value and then set the ComboBox style to DropDownList. In the absense of that, you have to deal with other issue such as what happens when the user types in a value that isn't in your list (rather than just blanks it).

For the second item, you'll need to handle the Parse event to convert "" to 0:

Binding b = new Binding("Text", this, "Money", true); b.Parse += delegate(object pSender, ConvertEventArgs pArgs) { pArgs.Value = (string.IsNullOrEmpty(pArgs.Value as string) ? 0 : pArgs.Value); }; this.textBox1.DataBindings.Add(b);

For the last issue, there are a couple of ways you can solve this. First, you can hook the TextChanged event on the TextBox and do validation as the user types into the TextBox. You can also hook the BindingComplete and set an error using the ErrorProvider as shown below. In addition, in the BindingCompleteEvent, you can set bArgs.Cancel to false to allow the user to leave the text box even with a bad value.

private void Form1_Load(object sender, EventArgs e) { TextBox tb1 = new TextBox(); TextBox tb2 = new TextBox(); ErrorProvider ep = new ErrorProvider(this); tb1.Location = new Point(10, 10); tb2.Location = new Point(10, 35); Binding b = new Binding("Text", this, "Value", true); b.BindingComplete += delegate(object bSender, BindingCompleteEventArgs bArgs) { if ((bArgs.BindingCompleteContext == BindingCompleteContext.DataSourceUpdate) && (bArgs.BindingCompleteState == BindingCompleteState.Exception)) { ep.SetError(tb1, bArgs.Exception.Message); } else { ep.SetError(tb1, null); } }; tb1.DataBindings.Add(b); this.Controls.Add(tb1); this.Controls.Add(tb2); } private string _value=string.Empty; public string Value { get { return _value; } set { if (value.Length > 10) { throw new Exception("Value must be 10 characters or less"); } _value = value; } }

Joe

JoeStegman at 2007-9-8 >

Unfortunately, this is not as easy as I'd like it to be and will be specific to your data model. It's quite likely you're data model won't allow DBNull.Value for the "ValueMember" (primary ID), so you'll end up needing to do something slightly more complex such as both adding a null value to your data source and hooking format and parse events. The sample code below puts an "empty" Employee in the Northwind Employees table and displays the employee for the currently selected order (in Northwind, the Orders table has a FK to the Employees table). I put a "null" employee in the Employees table and then hook Format/Parse events to translate the null employee to DBNull.Value. In order to get this to work, you'll have to manually setup binding to the ComboBox selected value (it will need to happen after you add the "null" row). Note that the employeesBindingSource is bound to the employees table and the ordersBindingSource is bound to the Orders table.

Joe

DataRowView drv = (this.employeesBindingSource.AddNew() as DataRowView); drv["LastName"] = "[None]"; drv["FirstName"] = string.Empty; drv["EmployeeID"] = -1; drv.EndEdit(); DataView dv = (this.employeesBindingSource.List as DataView); dv.Sort = "LastName ASC"; this.employeeIDComboBox.DataSource = this.employeesBindingSource; this.employeeIDComboBox.DisplayMember = "LastName"; this.employeeIDComboBox.ValueMember = "EmployeeID"; Binding b = new Binding("SelectedValue", this.ordersBindingSource, "EmployeeID", true); this.employeeIDComboBox.DataBindings.Add(b); b.Format += delegate(object fSender, ConvertEventArgs fArgs) { ComboBox cb = (b.Control as ComboBox); if ((fArgs.Value is DBNull) || (fArgs.Value == null)) { fArgs.Value = -1; } }; b.Parse += delegate(object pSender, ConvertEventArgs pArgs) { ComboBox cb = (b.Control as ComboBox); if ((null != cb) && (string.IsNullOrEmpty(cb.Text))) { pArgs.Value = DBNull.Value; } };

JoeStegman at 2007-9-8 >

TextBox1.DataBindings("text").NullValue = ""

RobertRFreeman at 2007-9-8 >