setAnchor method
设置锚点
Implementation
void setAnchor(String? key, GlobalKey value, {bool override = true}) {
if (key != null) {
String $key = _getKey(key);
if (override) {
_anchorMap[$key] = value;
} else {
if (_anchorMap.containsKey($key) == false) {
_anchorMap[$key] = value;
}
}
}
}