CODEWITHSUNDEEP
dictionarydartflutter
Jesse
Jesse

Reputation: 3050

Flutter/Dart: How to access a single entry in a map/object

This might be a very simple question but I am having trouble finding an answer. I have a object/map that I would not like to iterate but access a specific key/value at an index.

For example:

var _results = {
  'Key_1' : 'Value_1',
  'Key_2' : 'Value_2', 
};

How would I access the index[1]'s key_2 and value_2?

I've tried _results[index], _results[index].value, _results[index].key and _results[index].toString() but all returning null.

Upvotes: 118

Views: 257387

Answers (7)

Muhammad Javed
Muhammad Javed

Reputation: 119

Map map = {"id": 1, "email": "[email protected]"};

If you have data in map like above and you want to show all keys of map then you've to do this:

print(map.keys);

and if you want to print only values of inside map then you've to do this:

print(map.values);

If you want to convert your map into list, one list contains only keys and other list contains only values then you have to do these steps:

var onlyKey = map.entries.toList();

and to print list index_vise print(onlyKey[0].key);

var onlyValues = map.values.toList();

and to print list index_vise print(onlyValues[0]);

Upvotes: -1

Jamirul islam
Jamirul islam

Reputation: 856

 void main() {
      print(map.keys);
      print(map.values);
    
      //Print map value
      print(map["1"]);
    
      //Print keys
      for(var i in map.keys){
        print(i);
      }
      //Print value
      for(var i in map.values){
        print(i);
      }
    
      //print keys
      map.keys.forEach((element) { 
        print(element);
      });
    
      // print value
      map.values.forEach((element) {
        print(element);
      });
      
    }
    
    Map<String, dynamic> map = {
      "1": "A",
      "2": "B",
      "3" : "C",
      "4" : "D"
    };

Upvotes: 1

Cevin Ways
Cevin Ways

Reputation: 984

This is what i do to access object inside list in flutter : 

getOrderType() async{
    setState(() {
      order.add(new OrderTransactionTypeModel("1", "table", "TABLE"));
      order.add(new OrderTransactionTypeModel("10", "freeTable", "FREE TABLE"));
      order.add(new OrderTransactionTypeModel("7", "jasa", "JASA"));
      order.add(new OrderTransactionTypeModel("2", "bungkus", "BUNGKUS"));
      order.add(new OrderTransactionTypeModel("4", "delivery", "DELIVERY"));
      order.add(new OrderTransactionTypeModel("6", "ojekOnline", "OJEK ONLINE"));
      order.add(new OrderTransactionTypeModel("11", "reservasi", "RESERVASI"));
      order.add(new OrderTransactionTypeModel("99", "lainnya", "LAINNYA"));

      var mappedOrder = order.map((n) => 'Id: ${n.orderId} name: ${n.orderName}');
    });

    print(mappedOrder.toString());
  }

Upvotes: 1

Fellipe Sanches
Fellipe Sanches

Reputation: 8135

To print a value of a key, just use:

void main(){

  var results = {
  'usd' : 3.80,
  'eur' : 4.10, 
  'gbp' : 4.90, 
  };

  print(results['usd']); //3.80
}

Upvotes: 42

lrn
lrn

Reputation: 71653

A map allows looking up values by keys. So:

print(_results["Key_1"]);  // prints "Value_1"

A map is not a list of pairs, you cannot access by index.

You can access the keys, values and entries (pairs of key and value) as Iterables. 

for (var key in _results.keys) print(key); // prints Key_1 then Key_2
for (var value in _results.values) print(value); // prints Value_1 then Value_2
for (var entry in _results.entries) {
  print(entry.key);
  print(entry.value);
}

You can even convert the entries to a list if you really want to index by integer:

var entryList = _results.entries.toList();
print(entryList[0].key);  // prints "Key_1"

Still, this is not what maps are designed and optimized for. The map literal you wrote will iterate the entries, and their keys and values, in the order they occur in the source, but not all maps guarantee that. If you actually need a list of pairs of strings, I'd recommend making your data that from the beginning, instead of using a map. It will very likely be more efficient, and possibly easier to read.

Upvotes: 186

Randal Schwartz
Randal Schwartz

Reputation: 44066

A map is by nature "unordered", except by accident of some implementations. So there's not a "first" key/value pair, so your original question doesn't make sense.

Upvotes: 5

EdHuamani
EdHuamani

Reputation: 1897

convert values ​​to List:

var _list = _results.values.toList();

get by index:

print(_list[1]);

Upvotes: 88

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