File Attributes in Dart#

Introduction#

File attributes are key metadata that provide information about a file, such as its size, creation date, last modification date, and permissions. Understanding and retrieving these attributes are crucial for applications that involve file handling and management. In Dart, the dart:io library offers several methods to access these attributes efficiently.

About#

The File class in Dart provides easy-to-use methods to retrieve various file attributes. Some of the key attributes include:

• File Size: The size of the file in bytes.
• Last Modified: The date and time the file was last modified.
• Creation Time: The time the file was created (note: this attribute may not be available on all platforms).
• File Permissions: Information on read, write, and execute permissions.

These attributes allow developers to handle files more effectively, such as managing large files, monitoring changes, or ensuring correct file permissions.

How to Use#

Key Methods to Access File Attributes#

• stat(): This method provides all the file’s statistics, such as size, modified time, etc., in a single call.
• length(): Returns the size of the file.
• lastModified(): Returns the last modified date and time of the file.
• exists(): Checks if a file exists before retrieving its attributes.

Method Signatures:#

Future<FileStat> stat();
Future<int> length();
Future<DateTime> lastModified();

How It Works#

1. Asynchronously Retrieving File Attributes: Most of the file attribute methods are asynchronous, meaning they return Future objects. You need to await the results to access the actual values.
2. File Statistics Object: The File.stat() method returns a FileStat object that contains multiple attributes such as size, modified time, accessed time, and mode.
3. Exception Handling: Since these operations involve interacting with the file system, wrapping the code in try-catch blocks ensures that the program handles errors (e.g., file not found) gracefully.

Example#

• Example 1: Accessing Basic File Attributes

import 'dart:io';

void main() async {
  String filePath = 'example.txt'; // Specify the file path
  File file = File(filePath);

  try {
    if (await file.exists()) {
      // Fetch file size
      int fileSize = await file.length();
      print('File size: $fileSize bytes');

      // Fetch last modified date
      DateTime lastModified = await file.lastModified();
      print('Last modified: $lastModified');
    } else {
      print('File does not exist.');
    }
  } catch (e) {
    print('Error accessing file attributes: $e');
  }
}

• Example 2: Accessing File Statistics (All Attributes)

import 'dart:io';

void main() async {
  String filePath = 'example.txt'; // Specify the file path
  File file = File(filePath);

  try {
    if (await file.exists()) {
      // Get file statistics
      FileStat stats = await file.stat();
      print('File size: ${stats.size} bytes');
      print('Last modified: ${stats.modified}');
      print('File type: ${stats.type}');
    } else {
      print('File does not exist.');
    }
  } catch (e) {
    print('Error retrieving file statistics: $e');
  }
}

Explanation:#

• length(): Fetches the size of the file in bytes.
• lastModified(): Retrieves the timestamp when the file was last modified.
• stat(): Returns multiple file attributes at once, such as the size, type, last modified, accessed time, and mode (file permissions).
• Error Handling: The try-catch block ensures that any file operation errors are caught and handled properly.

Summary#

• Dart’s dart:io library provides methods like stat(), length(), and lastModified() to retrieve file attributes.
• Accessing file attributes asynchronously ensures non-blocking I/O operations.
• Handling file attributes effectively can help manage files based on size, modification time, and permissions.
• Always check if a file exists before attempting to retrieve its attributes to avoid errors.

These methods offer flexibility for managing files and their metadata, making your Dart applications more robust and efficient in handling file-related tasks.