In Dart programming language used for Flutter app development, checking if a specific value exists within an array or list is quite common. However, the correct method to use depends on whether you’re dealing with a primitive data type (like integers or strings) and storing it as values within your list or if you have a List of class objects.
For the former case where you’re checking for existence in a simple array containing integers, strings, etc., using the contains method is appropriate. This method works by scanning through all elements in the collection and returning true if any match what you’re looking for, false otherwise.
Contains Method
The contains method is straightforward to use:
list.contains(x);
This will return a boolean value indicating whether x exists within your list or not. It’s particularly useful when working with simple data types like integers or strings as values in your array.
Working with Class Objects
If, however, you’re dealing with a List of class objects, things become slightly more complex because the contains method doesn’t directly apply to custom class objects. You’d need another approach:
class DownloadedFile { String Url; String location; } ListlistOfDownloadedFile = List(); listOfDownloadedFile.add(...); // Now check if a specific value is inside this list var contain = listOfDownloadedFile.where((element) => element.Url == "your URL link"); if (contain.isEmpty) //value not exists else //value exists
Here, you’re essentially filtering the list based on whether the Url matches a certain value. This method effectively tells you if such an object exists within your collection.
Better Approach?
There might be even better ways to achieve this depending on your specific needs or the size of your data. Using the where function is one straightforward approach, but other methods like using the firstWhere method could also work effectively, especially if you’re looking for the first occurrence rather than checking existence in general.
Conclusion
In conclusion, when working with Dart for Flutter app development and needing to check values within arrays or lists, use contains for simple data types. For Lists of custom class objects, filter using methods like where. Always look into more efficient methods as per your project’s needs.