How to Fix “Argument Type ‘Map’ Can’t Be Assigned to the Parameter Type ‘Map’” Error in Dart

You may come across an error message that says “the argument type ‘Map<dynamic, dynamic>’ can’t be assigned to the parameter type ‘Map<String, dynamic>’.” This error occurs when you try to assign a map with dynamic keys or values to a map with specific key and value types. In this tutorial, we’ll show you how to fix this error and ensure that your code works as expected.

Define the Type of the Map: To fix this error, you need to specify the type of the map when you create it. Instead of using ‘Map<dynamic, dynamic>’, you can use ‘Map<String, dynamic>’ to define a map with string keys and dynamic values.

Map<String, dynamic> myMap = {'name': 'John', 'age': 30};

In this example, we defined a map called ‘myMap’ with string keys and dynamic values.

Type Cast the Map: If you have a map with dynamic keys or values and you need to assign it to a map with specific key and value types, you can use type casting to convert the map.

Map<dynamic, dynamic> myDynamicMap = {'name': 'John', 'age': 30};
Map<String, dynamic> myStringMap = Map<String, dynamic>.from(myDynamicMap);

In this example, we defined a map called ‘myDynamicMap’ with dynamic keys and values, and then used ‘Map<String, dynamic>.from()’ to type cast the map to a map with string keys and dynamic values.

Use Generics: Another way to avoid this error is to use generics to define the type of the map when you declare it.

Map<String, dynamic> myMap = <String, dynamic>{'name': 'John', 'age': 30};

In this example, we used the ‘<String, dynamic>’ syntax to define the type of the map when we declared it.

That’s it! By following these methods, you can fix the “Argument Type ‘Map<dynamic, dynamic>’ Can’t Be Assigned to the Parameter Type ‘Map<String, dynamic>’” error and ensure that your code works as expected.