f8.1/sdk/dart/package-fuchsia_vfs_vfs/PseudoFile/PseudoFile.readWrite.md

# PseudoFile.readWrite constructor




    *[<Null safety>](https://dart.dev/null-safety)*



PseudoFile.readWrite(int _capacity, [ReadFn](../../package-fuchsia_vfs_vfs/ReadFn.md)? _readFn, [WriteFn](../../package-fuchsia_vfs_vfs/WriteFn.md)? _writeFn)


<p>Creates new <a href="../../package-fuchsia_vfs_vfs/PseudoFile-class.md">PseudoFile</a> backed by the specified read and write handlers.</p>
<p>The read handler is called every time a read operation is performed on the file.  It is only
allowed to read at offset 0, and all of the content returned by the handler is returned by the
read operation.  Subsequent reads act the same - there is no seek position, nor ability to read
content in chunks.</p>
<p>The write handler is called every time a write operation is performed on the file.  It is only
allowed to write at offset 0, and all of the new content should be provided to a single write
operation.  Subsequent writes act the same - there is no seek position, nor ability to write
content in chunks.</p>



## Implementation

```dart
PseudoFile.readWrite(this._capacity, this._readFn, this._writeFn)
    : assert(_writeFn != null),
      assert(_readFn != null),
      assert(_capacity > 0);
```