PrismLibrary/Prism · error · NotImplementedException

The Keyboard Type value

Error message

The Keyboard Type value {keyboardType} is not supported. Please create and register an implementation of IKeyboardMapper to support this value.

What it means

Prism.Maui's KeyboardMapper maps a KeyboardType enum to a MAUI Keyboard instance via a switch expression; the default arm throws NotImplementedException because no registered IKeyboardMapper implementation can handle the given value. It signals an enum value outside the supported set or a custom value lacking a mapper.

Solutions

Use only the supported KeyboardType values: Chat, Email, Numeric, Plain, Telephone, Text, Url.
Register a custom IKeyboardMapper in the container that handles your additional values.
Validate/normalize any int-backed value before casting to KeyboardType.
Check for enum drift after package upgrades and re-map stored values.

Example fix

// before
var keyboard = keyboardMapper.Map((KeyboardType)rawInt); // rawInt invalid
// after
if (Enum.IsDefined(typeof(KeyboardType), rawInt))
    var keyboard = keyboardMapper.Map((KeyboardType)rawInt);

Defensive patterns

Strategy: validation

Validate before calling

if (!Enum.IsDefined(typeof(KeyboardType), keyboardType))
    throw new ArgumentOutOfRangeException(nameof(keyboardType), $"Unsupported KeyboardType: {keyboardType}");

Type guard

bool IsSupportedKeyboardType(KeyboardType t) => t is KeyboardType.Chat or KeyboardType.Email or KeyboardType.Numeric or KeyboardType.Plain or KeyboardType.Telephone or KeyboardType.Text or KeyboardType.Url;

Try / catch

try { var kb = mapper.Map(keyboardType); }
catch (NotImplementedException ex) { /* fall back to Keyboard.Plain, log ex.Message */ }

Prevention

Only pass enum-defined KeyboardType values; never cast raw ints unchecked
Register a custom IKeyboardMapper if you extend the enum
Re-check stored keyboard values after MAUI/Prism upgrades

When it happens

Trigger: Passing a KeyboardType value not handled by the switch (e.g. an out-of-range cast like (KeyboardType)99, a newer enum member added in a MAUI/Prism update, or a custom KeyboardType with no custom IKeyboardMapper registered).

Common situations: Storing keyboard type in config/preferences as int and casting invalid values; upgrading Prism.Maui or .NET MAUI where enum values shifted; defining an app-specific extended enum and feeding it to the default mapper.

Understand the failure class

Background: Invalid enum value errors: "Unknown type", "Invalid scope", "must be one of" — when a string is not on the library's allowed list — this error's family across 23 libraries.

Related errors

AI-assisted analysis of PrismLibrary/Prism@358118cd64 (2026-09-15). Data as JSON: /api/errors/e7fb06b75cb8cc59. Report an issue: GitHub.

Appendix: source

Thrown at src/Maui/Prism.Maui/AppModel/KeyboardMapper.cs:25

{
    /// <summary>
    /// Maps the <see cref="KeyboardType"/> to a <see cref="Keyboard"/>
    /// </summary>
    /// <param name="keyboardType">The Keyboard type.</param>
    /// <returns>The <see cref="Keyboard"/>.</returns>
    public virtual Keyboard Map(KeyboardType keyboardType)
    {
        return keyboardType switch
        {
            KeyboardType.Chat => Keyboard.Chat,
            KeyboardType.Default => Keyboard.Default,
            KeyboardType.Email => Keyboard.Email,
            KeyboardType.Numeric => Keyboard.Numeric,
            KeyboardType.Plain => Keyboard.Plain,
            KeyboardType.Telephone => Keyboard.Telephone,
            KeyboardType.Text => Keyboard.Text,
            KeyboardType.Url => Keyboard.Url,
            _ => throw new NotImplementedException($"The Keyboard Type value {keyboardType} is not supported. Please create and register an implementation of IKeyboardMapper to support this value.")
        };
    }
}

View on GitHub (pinned to 358118cd64)