How to use DropDownButton for dynamic list in flutter? - flutter

Question

I am trying to implement dynamic dropdownButton in my app where the items of dropdown is going to come from the names of columns in my excel sheet. I am able to show all the columns of excel but I couldn't able to trace the index of column which the user is selecting from the dropdown.
I tried to make a map of dropdownitems like this in which the key is the index and value is the DropdownMenuItem like this :
late int selectedIndex; //where I want to store the selected index
late String initialDropDownVal;
List<Map<int,DropdownMenuItem<String>>> dropdownItems = [];
Then I added some values by iterating the columns of excel using a for loop :
excel = Excel.decodeBytes(bytes);
sheet = excel['Sheet1'];
for(int i = 1; i< sheet.maxCols; ++i){
var cell = sheet.cell(CellIndex.indexByColumnRow(rowIndex: 0, columnIndex: i));
String val = cell.value.toString();
if(val=="null"){
break;
}else{
if(i==1){
initialDropDownVal = val;
}
var newItem = DropdownMenuItem(
child: Text(val),
value: val,
);
dropdownItems.add({i:newItem});
}
}
But I could not able to map the values in items attribute of DropdownButton, I tried to implement like this but this is throwing error
DropdownButton(
value: selectedVal,
icon: const Icon(Icons.keyboard_arrow_down),
items: dropdownItems.map((int i,DropdownMenuItem<String> p) => p).toList(),
onChanged: (String? value){
setState(() {
initialDropDownVal = value!;
});
})
And I am not sure how to change set the selectedIndex in onChanged function. Please help me in this. Thanks

Answer 1

late int selectedIndex; //where I want to store the selected index
late String initialDropDownVal;
List<DropdownMenuItem<String>> dropdownItems = [];
excel = Excel.decodeBytes(bytes);
sheet = excel['Sheet1'];
for(int i = 1; i< sheet.maxCols; ++i){
var cell = sheet.cell(CellIndex.indexByColumnRow(rowIndex: 0, columnIndex: i));
String val = cell.value.toString();
if(val=="null"){
break;
}else{
if(i==1){
initialDropDownVal = val;
}
var newItem = DropdownMenuItem(
child: Text(val),
value: val,
);
dropdownItems.add(newItem);
}
}
DropdownButton(
value: selectedVal,
icon: const Icon(Icons.keyboard_arrow_down),
items: dropdownItems,
onChanged: (String? value){
setState(() {
initialDropDownVal = value!;
selectedIndex=dropdownItems.indexWhere((i)=>i.value==value);
});
})

Answer 2

late int selectedIndex; //where I want to store the selected index
late String initialDropDownVal;
List<Map<String,int>> dropdownItems = [];
excel = Excel.decodeBytes(bytes);
sheet = excel['Sheet1'];
for(int i = 1; i< sheet.maxCols; ++i){
var cell = sheet.cell(CellIndex.indexByColumnRow(rowIndex: 0, columnIndex: i));
String val = cell.value.toString();
if(val=="null"){
break;
}else{
if(i==1){
initialDropDownVal = val;
}
dropdownItems.add({val:i});
}
}
DropdownButton(
value: selectedVal,
icon: const Icon(Icons.keyboard_arrow_down),
items: dropdownItems.map((e) {
return DropdownMenuItem(
child: Text(e.keys.first),
value: e.keys.first,
);
}).toList(),
onChanged: (String? value){
setState(() {
initialDropDownVal = value!;
for(int i = 0; i< dropdownItems.length; ++i){
if(dropdownItems[i].keys.first==value){
setState(() {
selectedIndex = dropdownItems[i].values.first;
});
break;
}
}
});
}),
)