Handling Null and Empty Values

C1Input provides rules for handling NULL (DBNull) values in data‑entry controls. The following sections describe how null and empty values are displayed and entered.

Displaying Null and Empty Values

When a control is not in edit mode or is read‑only, null values are displayed according to the NullText property, which can be overridden in DisplayFormat. If EmptyAsNull is set to True (default: False), empty strings are also displayed using the NullText value. In edit mode, the NullText and EmptyAsNull properties of EditFormat apply instead of those in DisplayFormat.

When edit mode is active with an EditMask, null values and empty strings appear as an empty mask with literals and prompt characters.

When editing a date‑time value and DateTimeInput is True, a null value appears as an empty control. When editing begins, the control assigns a non‑null value using the last assigned value or the current date.

When FormatType is set to UseEvent, the Formatting event is triggered only for non‑null values.

Entering Null and Empty Values

Unless EditMask mode is active, null values can be entered using the following methods:

• If the control text equals NullText, the resulting value is null. Comparison behavior depends on the CaseSensitive property.

• Clearing the control and entering an empty string produces a null value when C1TextBox.EmptyAsNull is True (default: False).

• In programmatic parsing, the Parsing event can return DBNull.

When a null value is entered, input string validation and parsing are skipped. PostValidation is still executed.

See Input String Validation (PreValidation), Parsing (Updating) Data, and Typed Value Validation (PostValidation).