How to Interrupt File Copy Operations in Qt?

Interrupting File Copy Operations

Handling large file transfers can present challenges, especially when users need to cancel operations in progress. This article explores ways to interrupt copy() and rename() operations, providing a solution that allows users to terminate these tasks without waiting for completion.

Problem Definition

Standard file operations in Qt, such as copy() and rename(), do not offer built-in mechanisms for interruption. This can lead to frustration for users who realize they have made a mistake and want to cancel a lengthy operation.

Solution: Custom Copy Helper

To address this issue, it is necessary to implement a custom solution using a derived QObject class. This class, known as CopyHelper, will manage the file copy process, track progress, and enable cancellation.

Here's an example implementation of the CopyHelper class:

class CopyHelper : public QObject {
    // ...
};

Operation Management

The CopyHelper class includes a begin() method that initializes the copy process, a step() method that performs incremental copying, and a cancel() method that allows users to terminate the operation.

Event Loop Integration

To ensure responsiveness, the step() method uses QMetaObject::invokeMethod() to schedule subsequent calls, allowing user events to be processed between copy iterations.

Progress Tracking

The CopyHelper class provides a progress property that tracks the completion percentage of the copy operation. This property can be monitored to update a progress bar or display user feedback.

Cancellation Handling

When the user cancels the operation, the CopyHelper class sets a isCancelled flag, which triggers cancellation logic in the step() method. The method deletes the partially copied file to prevent data corruption.

Using the Copy Helper

To use the CopyHelper class, instantiate it and call the begin() method to initiate the copy operation. Listen for the done() signal to determine when the copy has finished or has been canceled.

Conclusion

With this custom solution, it is possible to interrupt copy() and rename() operations in Qt, providing users with greater control and flexibility in file management.

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