ListView builder don't change in the required time - flutter

Question

I have search method who it can detect element form map and put theme in List variable where my List view builder takes his elements from.
the problem when I insert my word in Text Filed , list view builder doesn't change her statement until I close the keyboard and then I can see the change.
I want to see elements who I search currently
this my code :
_showDialog(){
var searchList = [];
int _manyOfWidgetShow = 0;
double heightOfListView = 0;
double higNumber(){
double _number;
if(_manyOfWidgetShow == 0){
_number = 0.25;
}
else if(_manyOfWidgetShow == 1){
_number = 0.3;
}else if(_manyOfWidgetShow == 2){
_number = 0.5;
}else if(_manyOfWidgetShow == 3){
_number = 0.6;
}
return _number;
}
void _showSearchReturn(String query){
List _items = [];
if(query.isNotEmpty){
testList.forEach( (element){
if(element["name"].toString().toLowerCase().startsWith(query) && _items.length < 3){
_items.add(element);
}
else if(query.length >= 2 && element["name"].toString().toLowerCase().contains(query) && _items.length < 3){
_items.add(element);
}
}
);
setState(() {
_manyOfWidgetShow = _items.length;
if(_manyOfWidgetShow != 0) {
heightOfListView = _manyOfWidgetShow * 50.0;
}else{
heightOfListView = 0;
}
searchList.clear();
searchList.addAll(_items);
});
}else{
setState(() {
_manyOfWidgetShow = _items.length;
if(_manyOfWidgetShow != 0){
heightOfListView = _manyOfWidgetShow * 50.0;
}else{
heightOfListView = 0;
}
searchList.clear();
});
}
}
showDialog(
context: context,
builder: (BuildContext context){
var _size = MediaQuery.of(context).size;
return Container(
child: Card(
shape: RoundedRectangleBorder(
borderRadius: BorderRadius.circular(30)
),
child: Container(
height: _size.height * higNumber(),
child: Column(
children: <Widget>[
Card(
margin: EdgeInsets.only(top:20,bottom: 15),
elevation: 4,
shape: RoundedRectangleBorder(
borderRadius: BorderRadius.circular(15)
),
child: Container(
alignment: Alignment.center,
padding: EdgeInsets.only(top: 15,bottom: 18),
child: TextField(
onChanged: (value){
_showSearchReturn(value);
},
scrollPadding: EdgeInsets.all(20),
autocorrect: false,
decoration: InputDecoration.collapsed(
hintText: "Movie name",
),
style: TextStyle(
fontSize: 20
),
strutStyle: StrutStyle(
fontWeight: FontWeight.bold,
height: 1.5
),
controller: searchText ,
cursorWidth: 2,
cursorColor: Color(0xff54C4A2),
textAlign: TextAlign.center,
),
)
),
Container(
height: heightOfListView,
child: ListView.builder(
itemCount: searchList.length,
shrinkWrap: true,
itemBuilder:(context,index){
return ItemInfo(searchList[index]["name"],searchList[index]["id"]);
}
)
),
Expanded(
child: Container(
alignment: Alignment.bottomLeft,
child: IconButton(icon: Icon(Icons.arrow_back_ios,color: Colors.black54,),
onPressed: (){
},
),
)
)
],
),
),
)
);
}
);
}