如何初始化 map 中的列表？
Map<String,Map<int,List<String>>> myMapList = Map();
我得到一个错误:
The method '[]' was called on null.
I/flutter (16433): Receiver: null
I/flutter (16433): Tried calling: [](9)
如何初始化 map 中的列表？
Map<String,Map<int,List<String>>> myMapList = Map();
我得到一个错误:
The method '[]' was called on null.
I/flutter (16433): Receiver: null
I/flutter (16433): Tried calling: [](9)
只需在创建 map 时添加元素，或稍后通过add次添加元素.例如:
var myMapList = <String, Map<int, List<String>>>{
'someKey': <int, List<String>>{
0: <String>['foo', 'bar'],
},
};
或
var m2 = <String, Map<int, List<String>>>{}; // empty map
m2['otherKey'] = <int, List<String>>{}; // add an empty map at the top level
m2['otherKey'][2] = <String>[]; // and an empty list to that map
m2['otherKey'][2].add('baz'); // and a value to that list
print(m2);
打印{otherKey: {2: [baz]}}张