lerp method Null safety

  1. @protected
T lerp(
  1. double t
)

Returns the value this variable has at the given animation clock value.

The default implementation of this method uses the +, -, and * operators on T. The begin and end properties must therefore be non-null by the time this method is called.

In general, however, it is possible for this to return null, especially when t=0.0 and begin is null, or t=1.0 and end is null.

Implementation

@protected
T lerp(double t) {
  assert(begin != null);
  assert(end != null);
  assert(() {
    // Assertions that attempt to catch common cases of tweening types
    // that do not conform to the Tween requirements.
    dynamic result;
    try {
      // ignore: avoid_dynamic_calls
      result = (begin as dynamic) + ((end as dynamic) - (begin as dynamic)) * t;
      result as T;
      return true;
    } on NoSuchMethodError {
      throw FlutterError.fromParts(<DiagnosticsNode>[
        ErrorSummary('Cannot lerp between "$begin" and "$end".'),
        ErrorDescription(
          'The type ${begin.runtimeType} might not fully implement `+`, `-`, and/or `*`. '
          'See "Types with special considerations" at https://api.flutter.dev/flutter/animation/Tween-class.html '
          'for more information.',
        ),
        if (begin is Color || end is Color)
          ErrorHint('To lerp colors, consider ColorTween instead.')
        else if (begin is Rect || end is Rect)
          ErrorHint('To lerp rects, consider RectTween instead.')
        else
          ErrorHint(
            'There may be a dedicated "${begin.runtimeType}Tween" for this type, '
            'or you may need to create one.',
          ),
      ]);
    } on TypeError {
      throw FlutterError.fromParts(<DiagnosticsNode>[
        ErrorSummary('Cannot lerp between "$begin" and "$end".'),
        ErrorDescription(
          'The type ${begin.runtimeType} returned a ${result.runtimeType} after '
          'multiplication with a double value. '
          'See "Types with special considerations" at https://api.flutter.dev/flutter/animation/Tween-class.html '
          'for more information.',
        ),
        if (begin is int || end is int)
          ErrorHint('To lerp int values, consider IntTween or StepTween instead.')
        else
          ErrorHint(
            'There may be a dedicated "${begin.runtimeType}Tween" for this type, '
            'or you may need to create one.',
          ),
      ]);
    }
  }());
  // ignore: avoid_dynamic_calls
  return (begin as dynamic) + ((end as dynamic) - (begin as dynamic)) * t as T;
}