In Dart, getting the value of a key in a hash (also known as a Map) can be done using square brackets notation []. Here's an example:
Map ages = {'John': 25, 'Sarah': 30, 'Tom': 35};
// Get the value of the key 'Sarah'
int sarahAge = ages['Sarah'];
print(sarahAge); // Output: 30
In the example above, we first create a Map called ages with three key-value pairs. Then we get the value of the key 'Sarah' using square brackets notation and assign it to a variable called sarahAge. Finally, we print the value of sarahAge, which should output 30.
It is important to note that if the key does not exist in the map, then Dart will return null. So, you can add check for null before using the value of a key. Here's an example:
Map colors = {'red': 'R', 'green': 'G', 'blue': 'B'};
String yellowCode = colors['yellow'];
if (yellowCode == null) {
print('Could not find code for the color yellow');
} else {
print('Yellow code is: $yellowCode');
}
In this example, we try to get the value of the key 'yellow' from the colors map. Since the key does not exist in the map, yellowCode is assigned null. We check if yellowCode is null and if so, we print a message saying that we could not find the code for the color yellow. Otherwise, we print the yellow code.