PP
Cocoa: How To Sync Views With A Color Preference Slider
2008-03-27
Much of my spare time is being used up very gradually writing a new photography-oriented application which I have code-named PP. This being my first sizable Mac app I also spend a lot of time reading, figuring out, rewriting code, and debugging as I encounter each challenge and work through it. While I am not going to blog the entire thing as I did with Random Wok, I am going to contribute pieces of what I have learned along the way.
PP has a thumbnail browser, as any photography-oriented app has, and I want to be able to control its background color. Just like Aperture I have a slider in my prefs panel that changes the gray level of the background and need to have that stored in the user's preferences. Since PP is a document-based app (I can have many document windows open at the same time), changing the browser background has to affect all the open documents and should do so in real time so the user can see the result.
Here is my prefs panel. Not much there yet:
The slider is set up to deliver a number between 0.0 and 1.0 and continuously return its state. The prefs panel XIB file also has an NSUserDefaultsController. The file's owner is a custom window controller:
I use three separate mechanisms for keeping everything in sync: actions, bindings, and notifications. Here is all of it together in one diagram:
The slider, NSUserDefaultsController and preferences file are joined together with bindings. I bind the slider's value to NSUserDefaultsController:
so that the controller is notified of all changes to the slider value. The NSUserDefaultsController keeps the prefs file on disk in sync. That is 100% of what is needed to handle the slider and the prefs. To set up the initial preferences I create the defaults in my application object:
To keep the browser background color in sync with the slider I have to be able to tell the browser's view controller that the value has changed so that it can get it from the NSUserDefaultsController object. This is a two-stage process: the slider tells its window controller via its action and the window controller tells the browser view controller through a notification:
To update the browser views, each instance of the browser view controller listens for notifications that indicate the color has changed and sends the appropriate message to its view:
The above two methods are called at appropriate times by the browser's window controller. The color is updated like this as the notification is received:
Finally, to set up the initial color the browser view controller implements this code:
That's it. Having set all of this up I can use the same mechanisms for handling other preferences and parameters that affect the browser or other views. I'm understanding the value of following the MVC pattern: it gives everything a place -- if you can figure out where that should be.
PP has a thumbnail browser, as any photography-oriented app has, and I want to be able to control its background color. Just like Aperture I have a slider in my prefs panel that changes the gray level of the background and need to have that stored in the user's preferences. Since PP is a document-based app (I can have many document windows open at the same time), changing the browser background has to affect all the open documents and should do so in real time so the user can see the result.
Here is my prefs panel. Not much there yet:
The slider is set up to deliver a number between 0.0 and 1.0 and continuously return its state. The prefs panel XIB file also has an NSUserDefaultsController. The file's owner is a custom window controller:
I use three separate mechanisms for keeping everything in sync: actions, bindings, and notifications. Here is all of it together in one diagram:
The slider, NSUserDefaultsController and preferences file are joined together with bindings. I bind the slider's value to NSUserDefaultsController:
so that the controller is notified of all changes to the slider value. The NSUserDefaultsController keeps the prefs file on disk in sync. That is 100% of what is needed to handle the slider and the prefs. To set up the initial preferences I create the defaults in my application object:
To keep the browser background color in sync with the slider I have to be able to tell the browser's view controller that the value has changed so that it can get it from the NSUserDefaultsController object. This is a two-stage process: the slider tells its window controller via its action and the window controller tells the browser view controller through a notification:
To update the browser views, each instance of the browser view controller listens for notifications that indicate the color has changed and sends the appropriate message to its view:
The above two methods are called at appropriate times by the browser's window controller. The color is updated like this as the notification is received:
Finally, to set up the initial color the browser view controller implements this code:
That's it. Having set all of this up I can use the same mechanisms for handling other preferences and parameters that affect the browser or other views. I'm understanding the value of following the MVC pattern: it gives everything a place -- if you can figure out where that should be.
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