Re: How to update preview in NSPrintPanel?
Re: How to update preview in NSPrintPanel?
- Subject: Re: How to update preview in NSPrintPanel?
- From: Quincey Morris <email@hidden>
- Date: Sun, 25 Dec 2011 17:44:19 -0800
On Dec 25, 2011, at 14:05 , Luc Van Bogaert wrote:
> I'm adding a custom user setting to a NSPrintPanel by adding an "accessory view controller" for a view that contains just one control (a checkbox) and which is loaded from a nib file. The checkbox's value has a binding to the view controller's "representedObject.printSettings.checkboxvalue" keypath. (The representedObject is a NSPrintInfo object).
>
> I have been able to verify that this binding works correctly.
>
> One thing I haven't gotten to work yet, is to automatically update the "preview" in the print panel when I chance the state of the checkbox. The preview updates itself correctly when I change one of the "built-in" settings, and it even correctly represents my own custom setting. But, how can I trigger an automatic update when I just change my own custom setting?
>
> I assume I should implement the "keyPathsForValuesAffectingPreview" protocol method in my accessory view controller, which I did, but so far without success. Here's my implementation:
>
> - (NSSet *)keyPathsForValuesAffectingPreview
> {
> return [NSSet setWithObjects:
> [NSString stringWithFormat:@"representedObject.printSettings.checkboxvalue"],
> nil];
> }
The immediate problem is that binding through a mutable dictionary like this (printSettings) isn't KVO compliant. Properties with values that are mutable objects are generally a problem for KVC/KVO, since it's really designed around the idea that property values are immutable objects like NSString and NSNumber.
The secondary problem is that you're trying, simultaneously, to use 2 different ways to get the accessory panel to update automatically, and both ways aren't working. If your binding was working, then 'keyPathsForValuesAffectingPreview' wouldn't be necessary. If you had a working 'keyPathsForValuesAffectingPreview', then I suspect you'd find that the checkbox still wouldn't change -- not because it wasn't updating, but because the change wouldn't be propagated.
I think the simplest approach is to add a "checkboxvalue" property to the view controller, bind the checkbox to File's Owner.checkboxvalue, and then make this property KVO-compliant:
1. The getter can just return self.representedObject.printSettings.checkboxvalue.
2. The setter can just change self.representedObject.printSettings.checkboxvalue.
3. The view controller needs to keep track of the current print settings object by observing its own "representedObject.printSettings" keypath.
4. Whenever the print settings object changes, the view controller needs to observe the "checkboxvalue" key of the new object and stop observing the same key of the old object.
5. Whenever the observed "checkboxvalue" changes, transfer the new value to self.checkboxvalue. Note that this starts a messaging loop between the 2 "checkboxvalue" properties, but the KVO machinery prevents this from being an infinite loop. You can short circuit the remaining minor duplication of effort, if you wish, by having your setter check the dictionary property value to avoid re-setting it to the existing value.
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