create method - Struct class - dart:ffi library (original) (raw)

create<T extends Struct> static method

1. @Since('3.4')

T create<T extends Struct>([

1. TypedData typedData,
2. int offset ])

Creates a struct view of bytes in typedData.

The created instance of the struct subclass will then be backed by the bytes at TypedData.offsetInBytes plus offset timesTypedData.elementSizeInBytes. That is, the getters and setters of the external instance variables declared by the subclass, will read an write their values from the bytes of the TypedData.buffer of typedData, starting at TypedData.offsetInBytes plus offset timesTypedData.elementSizeInBytes. The TypedData.lengthInBytes oftypedData must be sufficient to contain the sizeOf of the struct subclass. It doesn't matter whether the typedData is, for example, aUint8List, a Float64List, or any other TypedData, it's only treated as a view into a ByteBuffer, through its TypedData.buffer,TypedData.offsetInBytes and TypedData.lengthInBytes.

If typedData is omitted, a fresh ByteBuffer, with precisely enough bytes for the sizeOf of the created struct, is allocated on the Dart heap, and used as memory to store the struct fields.

If offset is provided, the indexing into typedData is offset byoffset times TypedData.elementSizeInBytes.

Example:

final class Point extends Struct {
  @Double()
  external double x;

  @Double()
  external double y;

  /// Creates Dart managed memory to hold a `Point` and returns the
  /// `Point` view on it.
  factory Point(double x, double y) {
    return Struct.create()
      ..x = x
      ..y = y;
  }

  /// Creates a [Point] view on [typedData].
  factory Point.fromTypedData(TypedData typedData) {
    return Struct.create(typedData);
  }
}

To create a struct object from a Pointer, use StructPointer.ref.

Implementation

@Since('3.4')
external static T create<T extends Struct>([TypedData typedData, int offset]);