> For the complete documentation index, see [llms.txt](https://apryse.gitbook.io/api-markdown-test/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://apryse.gitbook.io/api-markdown-test/ios/viewer/viewer/file-coordination.md).

# File coordination

Learn about file coordination in iOS using UIDocument and PTCoordinatedDocument by Apryse. Ensure data integrity and avoid conflicts when accessing shared files. Optimize your app's performance with c

File coordination is a system of ensuring that no two processes (or threads within a single process) can change a commonly accessed file in a way the other does not expect, which could result in unexpected behavior and data loss.

iOS provides the [`UIDocument`](https://developer.apple.com/uikit/uidocument/) abstract base class which enables a subclass to be notified of any changes to the file or its state, which in turn allows an adopting app the ability to coordinate its actions with others.

Apryse provides [`PTCoordinatedDocument`](https://sdk.apryse.com/api/ios/Classes/PTCoordinatedDocument.html), a concrete subclass of `UIDocument`, to coordinate reading and writing of PDF files (both locally and cloud stored) with other apps. `PTCoordinatedDocument` is compatible with both the [`DocumentViewer`](/api-markdown-test/ios/basic-operations/open/doc-view.md) and [`TabbedViewer`](/api-markdown-test/ios/basic-operations/open/doc-tabbed.md), and is used by our sample project Complete Reader. It is recommended to use a `PTCoordinatedDocument` to open a document whenever the document could be written to by another app.

Below is sample code showing how to open a coordinated document in a new `PTDocumentController`.

{% tabs %}
{% tab title="Swift" %}
{% code lineNumbers="true" %}

```swift
func presentDocument(at documentURL: URL?) {
    
    // Create a document viewer in which to show a document
    let documentViewController = PTDocumentController()
    
    // Ensure a URL is available
    guard let anURL = documentURL else { return }
    
    // Create a coordinated document backed by the PDF document at the file URL `documentURL`
    let coordinatedDocument = PTCoordinatedDocument(fileURL: anURL)

    // Create a weak reference to avoid a reference cycle
    weak var weakself = self

    // Open the coordinated document in the document viewer
    documentViewController.setCoordinatedDocument(coordinatedDocument, completionHandler: { error in
        
        // Create a strong self to ensure access during use
        guard let strongSelf = weakself else { return }
        
        // Create an empty navigation controller to host the document viewer
        let navigationController = UINavigationController(rootViewController: documentViewController)
        
        // Create a button to close the navigation controller#selector(sayHello(sender:))
        let item = UIBarButtonItem(barButtonSystemItem: .done, target: strongSelf, action: #selector(strongSelf.close(_:)))
        
        // Add the close button to the navigation controller
        documentViewController.navigationItem.setLeftBarButton(item, animated: false)
        
        strongSelf.view.setNeedsLayout()
        
        // Present the view controller
        strongSelf.present(navigationController, animated: true)
    })
    
}

// Method to dismiss the view controller
@objc func close(_ barButtonItem: UIBarButtonItem?) {
    self.dismiss(animated: true)
}
```

{% endcode %}
{% endtab %}

{% tab title="Obj-C" %}
{% code lineNumbers="true" %}

```objc
- (void)presentDocumentAtURL:(NSURL *)documentURL {
    
    // Create a document viewer in which to show a document
    self.documentViewController = [[PTDocumentController alloc] init];
    
    // Create a coordinated document backed by the PDF document at the file URL `documentURL`
    PTCoordinatedDocument* coordinatedDocument = [[PTCoordinatedDocument alloc] initWithFileURL:documentURL];
    
    // Create a weak pointer to avoid a reference cycle
    __weak typeof(self) weakself = self;
    
    // Open the coordinated document in the document viewer
    [self.documentViewController setCoordinatedDocument:coordinatedDocument completionHandler:^(NSError* error)
    {
        // Create a strong self to ensure access during use
        typeof(self) strongSelf = weakself;
        
        if( strongSelf )
        {
             // Create an empty navigation controller to host the document viewer
             UINavigationController *navigationController = [[UINavigationController alloc] initWithRootViewController:weakself.documentViewController];
            
             // Create a button to close the navigation controller
             UIBarButtonItem *item = [[UIBarButtonItem alloc] initWithBarButtonSystemItem:UIBarButtonSystemItemDone target:strongSelf action:@selector(close:)];
            
             // Add the close button to the navigation controller
             [strongSelf.documentViewController.navigationItem setLeftBarButtonItem:item animated:NO];
            
             [strongSelf.view setNeedsLayout];
            
             // Present the view controller
             [strongSelf presentViewController:navigationController animated:YES completion:nil];
        }
         
     }];
}

// Method to dismiss the view controller
-(void)close:(UIBarButtonItem*)barButtonItem
{
    [self dismissViewControllerAnimated:YES completion:Nil];
}
```

{% endcode %}
{% endtab %}
{% endtabs %}


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