The Flexible does the trick
Flexible
new Container( child: Row( children: <Widget>[ Flexible( child: new Text("A looooooooooooooooooong text")) ], ));
This is the official doc https://flutter.dev/docs/development/ui/layout#lay-out-multiple-widgets-vertically-and-horizontally on how to arrange widgets.
Remember that Flexible and also Expanded, should only be used within a Column, Row or Flex, because of the Incorrect use of ParentDataWidget.
Expanded
Column
Row
Flex
Incorrect use of ParentDataWidget
The solution is not the mere Flexible
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