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POCocoa: looking for a general strategy for programmatic manipulation of NSTextView storage without messing up undo
 

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  1. POCocoa: looking for a general strategy for programmatic manipulation of NSTextView storage without messing up undo
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    <p>I am writing a special-purpose text editor in cocoa that does things like automatic text substitution, inline text completions (ala <strong>Xcode</strong>), etc.</p> <p>I need to be able to programmatically manipulate the <code>NSTextView</code>’s <code>NSTextStorage</code> in response to 1) user typing, 2) user pasting, 3) user dropping text.</p> <p>I have tried two different general approaches and both of them have caused the <code>NSTextView</code>’s native undo manager to get out of sync in different ways. In each case, I am only using <code>NSTextView</code> delegate methods. I have been trying to avoid subclassing <code>NSTextview</code> or <code>NSTextStorage</code> (though I will subclass if necessary).</p> <p>The first approach I tried was doing the manipulations from within the <code>textView</code> <code>delegate</code>’s <code>textDidChange</code> method. From within that method, I analyzed what had been changed in the <code>textView</code> and then called a general purpose method for modifying text that wrapped the changes in the textStorage with calls to <code>shouldChangeTextInRange:</code> and <code>didChangeText:</code>. Some of the programmatic changes allowed clean undo’s but some did not.</p> <p>The second (and maybe more intuitive because it makes changes before the text actually appears in the <code>textView</code>) approach I tried was doing the manipulations from within the <code>delegate</code>’s <code>shouldChangeTextInRange:</code> method, again using the same general purpose storage modification method that wraps changes in the storage with a call to <code>shouldChangeTextInRange:</code> and <code>didChangeText:</code>. Since these changes were being triggered originally from within <code>shouldChangeTextInRange:</code>, I set a flag that told the inner call to <code>shouldChangeTextInRange:</code> to be ignored so as not to enter recursive blackholeness. Again, Some of the programmatic changes allowed clean undo’s but some did not (though different ones this time, and in different ways).</p> <p>With all that background, my question is, can someone point me to a general strategy for programmatically manipulating the storage of an <code>NSTextview</code> that will keep the undo manager clean and in sync?</p> <p>In which <code>NSTextview</code> delegate method should I pay attention to the text changes in the textView (via typing, pasting, or dropping) and do the manipulations to the <code>NSTextStorage</code>? Or is the only clean way to do this by subclassing either <code>NSTextView</code> or <code>NSTextStorage</code>?</p>
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    1. COMy app does most of its manipulations in `NSTextStorageDelegate`'s `-textStorageWillProcessEditing:`, but it only has to manipulate attributes, not characters. Still, that might be another thing for you to try.
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      1. USBrent Royal-Gordon
    2. COPlease elaborate on those "general purpose storage modification method[s] that wraps changes in the storage with a call to shouldChangeTextInRange: and didChangeText:". Doing something within a delagate method which recursively calls the same delegate method sounds fishy.
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      1. POCocoa: looking for a general strategy for programmatic manipulation of NSTextView storage without messing up undo
      1. USPierre Houston
    3. CO@smallduck: As it has been roughly two years since I asked this question originally and I abandoned the project - in large part because I could not solve this undo issue satisfactorily - I can't really remember a lot of the details. I did spend considerable development time trying to work it out and tried many other approaches besides what I wrote above. I know it is possible because Xcode's editor does it, but I never found a way to programmatically change text without throwing the undo manager out of sync.
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