Dart FileSystemMoveEvent
last modified April 4, 2025
The FileSystemMoveEvent class in Dart represents file system move
or rename operations. It's part of Dart's file system event monitoring API.
This event is triggered when files or directories are moved or renamed within a watched directory. It provides details about both old and new paths.
Basic Definition
FileSystemMoveEvent is a subclass of FileSystemEvent.
It contains information about file/directory move operations in the file system.
Key properties include the old path (source) and new path (destination) of the
moved item. It's emitted by Directory.watch() when moves occur.
Basic FileSystemMoveEvent Usage
This example shows how to watch for file move events in a directory.
import 'dart:io';
void main() async {
var dir = Directory('test_dir');
await dir.create();
var watcher = dir.watch();
watcher.listen((event) {
if (event is FileSystemMoveEvent) {
print('Move detected:');
print(' From: ${event.path}');
print(' To: ${event.destination}');
print(' Type: ${event.type}');
}
});
// Simulate a file move
var file = File('${dir.path}/test.txt');
await file.create();
await file.rename('${dir.path}/renamed.txt');
}
We create a directory watcher and listen for move events. When a file is renamed, the event provides both original and new paths. The type indicates move or rename.
$ dart main.dart Move detected: From: test_dir/test.txt To: test_dir/renamed.txt Type: FileSystemEvent.move
Handling Directory Moves
This example demonstrates detecting directory move operations.
import 'dart:io';
void main() async {
var dir = Directory('watch_dir');
await dir.create();
var watcher = dir.watch();
watcher.listen((event) {
if (event is FileSystemMoveEvent) {
print('Directory moved:');
print(' Source: ${event.path}');
print(' Target: ${event.destination}');
}
});
// Create and move a subdirectory
var subDir = Directory('${dir.path}/subdir');
await subDir.create();
await subDir.rename('${dir.path}/moved_subdir');
}
Directory moves trigger similar events to file moves. The event contains the original and new paths of the moved directory. This works recursively.
$ dart main.dart Directory moved: Source: watch_dir/subdir Target: watch_dir/moved_subdir
Distinguishing Move Types
This example shows how to differentiate between moves and renames.
import 'dart:io';
void main() async {
var dir = Directory('monitor_dir');
await dir.create();
var watcher = dir.watch();
watcher.listen((event) {
if (event is FileSystemMoveEvent) {
var isRename = event.path.split('/').last ==
event.destination.split('/').last;
print(isRename ? 'File renamed' : 'File moved');
print(' Old: ${event.path}');
print(' New: ${event.destination}');
}
});
// Test cases
var file = File('${dir.path}/original.txt');
await file.create();
// Rename (same directory)
await file.rename('${dir.path}/renamed.txt');
// Move (different directory)
var newDir = Directory('${dir.path}/new_location');
await newDir.create();
await File('${dir.path}/renamed.txt')
.rename('${newDir.path}/moved.txt');
}
We distinguish renames from moves by comparing parent directories. Renames keep the same parent directory while moves change it. Both trigger move events.
$ dart main.dart File renamed Old: monitor_dir/original.txt New: monitor_dir/renamed.txt File moved Old: monitor_dir/renamed.txt New: monitor_dir/new_location/moved.txt
Error Handling in Move Events
This example demonstrates error handling during file system move operations.
import 'dart:io';
void main() async {
var dir = Directory('error_dir');
await dir.create();
var watcher = dir.watch();
watcher.listen((event) {
if (event is FileSystemMoveEvent) {
print('Move event detected');
try {
var file = File(event.destination);
print('File exists: ${file.existsSync()}');
} catch (e) {
print('Error checking moved file: $e');
}
}
});
var file = File('${dir.path}/testfile.txt');
await file.create();
// Move to invalid location
try {
await file.rename('${dir.path}/nonexistent/subdir/file.txt');
} catch (e) {
print('Move failed: $e');
}
}
We handle potential errors when processing move events. The event fires even if the move operation fails, so destination validation is important.
$ dart main.dart Move event detected Error checking moved file: FileSystemException: Cannot open file, path = 'error_dir/nonexistent/subdir/file.txt' (OS Error: No such file or directory, errno = 2) Move failed: FileSystemException: Cannot rename file to 'error_dir/nonexistent/subdir/file.txt', path = 'error_dir/testfile.txt' (OS Error: No such file or directory, errno = 2)
Monitoring Multiple Events
This example shows handling multiple event types including move events.
import 'dart:io';
void main() async {
var dir = Directory('multi_event_dir');
await dir.create();
var watcher = dir.watch();
watcher.listen((event) {
switch (event.type) {
case FileSystemEvent.move:
print('Move event: ${event.path} → ${(event as FileSystemMoveEvent).destination}');
break;
case FileSystemEvent.create:
print('Create event: ${event.path}');
break;
case FileSystemEvent.delete:
print('Delete event: ${event.path}');
break;
case FileSystemEvent.modify:
print('Modify event: ${event.path}');
break;
}
});
// Trigger various events
var file = File('${dir.path}/demo.txt');
await file.create();
await file.writeAsString('content');
await file.rename('${dir.path}/renamed_demo.txt');
await file.delete();
}
We handle all file system event types with a switch statement. Move events are specifically cast to access the destination property. Each event type has its own case.
$ dart main.dart Create event: multi_event_dir/demo.txt Modify event: multi_event_dir/demo.txt Move event: multi_event_dir/demo.txt → multi_event_dir/renamed_demo.txt Delete event: multi_event_dir/renamed_demo.txt
Best Practices
- Filter events: Check event types before processing
- Handle errors: Validate paths after move events
- Resource management: Close watchers when done
- Performance: Avoid heavy processing in event handlers
- Cross-platform: Test behavior on different OSes
Source
Dart FileSystemMoveEvent Documentation
This tutorial covered Dart's FileSystemMoveEvent class with practical examples showing file and directory move detection, error handling, and event processing.
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