-[Not A Type retain]: message sent to deallocated

问题:

I have converted my app to use ARC.

Before I had the following line of code:

NSArray *colors = [NSArray arrayWithObjects:startColor, endColor, nil];

Since the implicit conversion of a non-Objective-C pointer type to 'id' is disallowed with ARC, I rewrote the line like this:

NSArray *colors = [NSArray arrayWithObjects:(__bridge id)startColor, (__bridge id)endColor, nil];

Everything works fine on the simulator, however on the device the app crashes on the mentioned line with the error message:

-[Not A Type retain]: message sent to deallocated instance

Any ideas how to solve it?

回答1:

This bridged cast may not work, as hatfinch describes in his answer here, because the CGColorRef returned from -CGColor may not hang around after your last reference to the UIColor that generates it. I thought this was a bug, based on the discussion in this Apple developer forum thread, but it was a misreading of how to manage the lifetime of these CGColorRefs.

One way that this will work is to use the built-in bridging provided by the -CGColor method on UIColor. Rather than saving out your CGColor to a temporary variable as you do above, you should be able to use something like the following:

NSArray *colors = [NSArray arrayWithObjects:(id)[color1 CGColor],
                                            (id)[color2 CGColor], nil];

with color1 and color2 being UIColor instances.

The bridging is taken care of for you by the -CGColor method, according to the "The Compiler Handles CF Objects Returned From Cocoa Methods" section of the Transitioning to ARC Release Notes. The documentation is currently missing the cast to id that I have above, which is required to get this to compile.

I've tested this, and it seems to work in my case, matching what Ben reports in the above-linked Developer Forums thread.

In addition to the above, you can explicitly retain and release the CGColorRefs returned from the -CGColor method and bridge them across in your NSArray, again as hatfinch shows here.

回答2:

Edit:
If you use UIColor's CGColor property, the CGColor will go away the moment you last reference the UIColor instance. To avoid this, "bridge" your colors directly in the function call:

NSArray *colors = [NSArray arrayWithObjects:[uiStartColor CGColor], [uiEndColor CGColor], nil];

This method is described in Apple's documentation

Original:
try assigning a variable: id color = (__bridge_transfer id)CGColorCreate(...); and do nothing else with the direct return value of CGColorCreate()

回答3:

Thanks @Brad for the tip of -CGColor!

my app crash on following line, which will be invoked by a NSInvocation object.

    CGContextSetFillColorWithColor(context, [UIColor whiteColor].CGColor);

the workaround is defining a color property and use it instead.

    @property(strong, nonatomic) UIColor *backgroundColor;
    ......
    self.backgroundColor = [UIColor whiteColor];
    ......
    CGContextSetFillColorWithColor(context, self.backgroundColor.CGColor);