openWrite method

Creates a new independent IOSink for the file.

The IOSink must be closed when no longer used, to free system resources.

An IOSink for a file can be opened in two modes:

• FileMode.write: truncates the file to length zero.
• FileMode.append: sets the initial write position to the end of the file.

When writing strings through the returned IOSink the encoding specified using encoding will be used. The returned IOSink has an encoding property which can be changed after the IOSink has been created.

The returned IOSink does not transform newline characters ("\n") to the platform's conventional line ending (e.g. "\r\n" on Windows). Write a Platform.lineTerminator if a platform-specific line ending is needed.

If an error occurs while opening or writing to the file, the IOSink.done IOSink.flush, and IOSink.close futures will all complete with a FileSystemException. You must handle errors from the IOSink.done future or the error will be uncaught.

For example, FutureExtensions.ignore the IOSink.done error and remember to await the IOSink.flush and IOSink.close calls within a try/catch:

final sink = File('/tmp').openWrite(); // Can't write to /tmp
sink.done.ignore();
sink.write("This is a test");
try {
  // If one of these isn't awaited, then errors will pass silently!
  await sink.flush();
  await sink.close();
} on FileSystemException catch (e) {
  print('Error writing file: $e');
}

To handle errors asynchronously outside of the context of IOSink.flush and IOSink.close, you can Future.catchError the IOSink.done.

final sink = File('/tmp').openWrite(); // Can't write to /tmp
sink.done.catchError((e) {
 // Handle the error.
});