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TextEditingController textFieldController = new TextEditingController();
Clipboard.setData(new ClipboardData(text: "copied text")); // copy text
onPressed() async { // onPress function of button
ClipboardData data = await Clipboard.getData('text/plain');
setState(() {
textFieldController.text = data.text.toString(); // this will paste "copied text" to textFieldController
});
}