如何在 flutter 中使用 DropDownButton 作为动态列表?
How to use DropDownButton for dynamic list in flutter?
我正在尝试在我的应用程序中实现动态 dropdownButton,其中下拉项目将来自我的 excel sheet 中的列名称。我能够显示 excel 的所有列,但我无法跟踪用户从下拉列表中选择的列的索引。
我尝试制作一个像这样的下拉项映射,其中键是索引,值是 DropdownMenuItem,如下所示:
late int selectedIndex; //where I want to store the selected index
late String initialDropDownVal;
List<Map<int,DropdownMenuItem<String>>> dropdownItems = [];
然后我通过使用 for 循环迭代 excel 的列来添加一些值:
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});
}
}
但我无法映射 DropdownButton 的 items 属性中的值,我尝试这样实现,但这是抛出错误
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!;
});
})
而且我不确定如何在 onChanged 函数中更改设置 selectedIndex。请帮助我。谢谢
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);
});
})
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;
}
}
});
}),
)
我正在尝试在我的应用程序中实现动态 dropdownButton,其中下拉项目将来自我的 excel sheet 中的列名称。我能够显示 excel 的所有列,但我无法跟踪用户从下拉列表中选择的列的索引。
我尝试制作一个像这样的下拉项映射,其中键是索引,值是 DropdownMenuItem,如下所示:
late int selectedIndex; //where I want to store the selected index
late String initialDropDownVal;
List<Map<int,DropdownMenuItem<String>>> dropdownItems = [];
然后我通过使用 for 循环迭代 excel 的列来添加一些值:
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});
}
}
但我无法映射 DropdownButton 的 items 属性中的值,我尝试这样实现,但这是抛出错误
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!;
});
})
而且我不确定如何在 onChanged 函数中更改设置 selectedIndex。请帮助我。谢谢
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);
});
})
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;
}
}
});
}),
)