Protocol: NSFilePresenter

Tells the delegate that some entity wants to delete an item that is inside of a presented directory. (required) This method is relevant for applications that present directories. This might occur if the delegate manages the contents of a directory or manages a file that is implemented as a file package. When called, your implementation of this method should take whatever actions needed to update your application to handle the deletion of the specified file. Important: If you implement this method, you must execute the block in the completionHandler parameter at the end of your implementation. The system waits for you to execute that block before allowing the other object to delete the item at the specified URL. Therefore, failure to execute the block could stall threads in your application or in other processes.

Tells your object that the presented item’s contents or attributes changed. You can use this method to update your internal data structures to reflect the changes to the presented item. This method reports both changes to the file’s contents, such as the data in a file or the files in a directory, or the attributes of the item, such as whether the Hide extension checkbox of a file was toggled.Because this method notifies you of both attribute and content changes, you might want to check the modification date before needlessly rereading the contents of a file. To do that, you must store the date when your object last made changes to the file and compare that date with the item’s current modification date. Use the coordinateReadingItemAtURL:options:error:byAccessor: method of a file coordinator to ensure exclusive access to the file when reading the current modification date.

Tells the delegate that a new version of the file or file package was added. (required) Your delegate can use this method to determine how to incorporate data from the new version of the file or file package. If the file has not been modified by your code, you might simply update to the new version quietly. However, if your application has its own changes, you might need to ask the user how to proceed.

Tells the delegate that a version of the file or file package was removed. (required) Your delegate can use this method to determine how to handle the loss of the specified file version. You can try to revert the presented document to a previous version or you might want to prompt the user about how to proceed.

Tells your object that the presented item moved or was renamed. Use this method to update the value returned by the presentedItemURL property of your object.

Tells the delegate that some other entity resolved a version conflict for the presenter’s file or file package. (required) Your delegate can use this method to respond to the resolution of a version conflict by a different file presenter. This might occur if a version of your application running on another device resolves the conflict first. You might then use this method to update your user interface to indicate that there is no longer a conflict.

Tells the delegate that the item inside the presented directory gained a new version. (required) Your delegate can use this method to determine how to incorporate data from the new version of the item. This might involve incorporating the version silently or asking the user about how to proceed.

Tells the delegate that the item inside the presented directory lost an existing version. (required) Your delegate can use this method to determine how to handle the loss of the specified file version. For an old version, you might not have to do anything. However, if your application is currently using the lost version, you would need to update your application’s user interface or prompt the user about how to proceed.

Tells the delegate that an item in the presented directory moved to a new location. (required) This method is relevant for applications that present directories. This might occur if the delegate manages the contents of a directory or manages a file that is implemented as a file package. Your implementation of this method should take whatever actions necessary to handle the change in location of the specified item. For example, you might update references to the item in your application’s data structures and refresh your user interface.If the presented directory is a file package, the system calls the presentedItemDidChange method if your delegate does not implement this method.

Tells the delegate that the item inside the presented directory had a version conflict resolved by an outside entity. (required) Your delegate can use this method to respond to the resolution of a version conflict by a different file presenter. This might occur if a version of your application running on another device resolves the conflict first. You might then use this method to update your user interface to indicate that there is no longer a conflict.

Tells the delegate that an item was added to the presented directory. (required) This method is relevant for applications that present directories. This might occur if the delegate manages the contents of a directory or manages a file that is implemented as a file package. Your implementation of this method should take whatever actions necessary to incorporate the new file or directory into the presented content. For example, you might add the new item to your application’s data structures and refresh your user interface.If the presented directory is a file package, the system calls the presentedItemDidChange method if your delegate does not implement this method.

Tells the delegate that the contents or attributes of the specified item changed. (required) This method is relevant for applications that present directories. This might occur if the delegate manages the contents of a directory or manages a file that is implemented as a file package. Your implementation of this method should take whatever actions necessary to handle the change in content or attributes of the specified item.If the presented directory is a file package, the system calls the presentedItemDidChange method if your delegate does not implement this method.

Notifies your object that another object or process wants to read the presented file or directory. You use this method to provide an appropriate response when another object wants to read from your presented URL. For example, when this method is called, you might temporarily stop making changes to the file or directory. After taking any appropriate steps, you must execute the block in the reader parameter to let the waiting object know that it may now proceed with its task. If you want to be notified when the reader has completed its task, pass your own block to the reader and use that block to reacquire the file or URL for your own uses. Important: If you implement this method, you must execute the block in the reader parameter as part of your implementation. The system waits for you to execute that block before allowing the reader to operate on the file. Therefore, failure to execute the block could stall threads in your application or other processes until the user takes corrective actions. The following listing shows a simple implementation of this method that sets a Boolean flag that the file being monitored is not writable at the moment. After setting the flag, it executes the reader block and passes in yet another block for the reader to execute when it is done. Your implementation of this method is executed using the queue in the presentedItemOperationQueue property. Your reacquirer block is executed on the queue associated with the reader.

Notifies your object that another object or process wants to write to the presented file or directory. You use this method to provide an appropriate response when another object wants to write to your presented URL. For example, when this method is called, you would likely stop making changes to the file or directory. After taking any appropriate steps, you must execute the block in the writer parameter to let the waiting object know that it may now proceed with its task. If you want to be notified when the writer has completed its task, pass your own block to the writer and use that block to reacquire the file or URL for your own uses. Important: If you implement this method, you must execute the block in the writer parameter at the end of your implementation. The system waits for you to execute that block before allowing the writer to operate on the file. Therefore, failure to execute the block could stall threads in your application or other processes. If the writer changes the file or directory, you do not need to incorporate those changes in your reacquirer block. Instead, implement the presentedItemDidChange method and use it to detect when a writer actually wrote its changes to disk. The following listing shows a simple implementation of this method that sets a Boolean flag that the file being monitored is not writable at the moment. After setting the flag, it executes the writer block and passes in yet another block for the writer to execute when it is done. Your implementation of this method is executed using the queue in the presentedItemOperationQueue property. Your reacquirer block is executed on the queue associated with the writer.

Tells your object to save any unsaved changes for the presented item. The file coordinator calls this method to ensure that all objects trying to access the file or directory see the same contents. Implement this method if your object can change the presented item in a way that requires you to write those changes back to disk. If your presenter object does not make changes that need to be saved, you do not need to implement this method.Important: If you implement this method, you must execute the block in the completionHandler parameter at the end of your implementation. The system waits for you to execute that block before allowing other objects to operate on the file. Therefore, failure to execute the block could stall threads in your application or other processes.