Question

I’d like to call (void)setDoubleValue:(double)value using performSelectorOnMainThread:.

What I thought would work is:

NSNumber *progress = [NSNumber numberWithDouble:50.0];
[progressIndicator performSelectorOnMainThread:@selector(setDoubleValue:)
                                    withObject:progress
                                 waitUntilDone:NO];

Didn’t work.

Then I implemented a helper method:

- (void)updateProgressIndicator:(NSNumber *)progress
{
    [progressIndicator setDoubleValue:[progress doubleValue]];
}

Works, but not really clean.

After that I tried it with NSInvocation.

NSInvocation *setDoubleInvocation;;
SEL selector = @selector(setDoubleValue:);
NSMethodSignature *signature;
signature = [progressIndicator methodSignatureForSelector:selector];
setDoubleInvocation = [NSInvocation invocationWithMethodSignature:signature];
[setDoubleInvocation setSelector:selector];
[setDoubleInvocation setTarget:progressIndicator];

double progress = 50.0;
[setDoubleInvocation setArgument:&progress atIndex:2];

[setDoubleInvocation performSelectorOnMainThread:@selector(invoke)
                                      withObject:nil
                                   waitUntilDone:NO];

This solution works, but it uses a lot of code and is quite slow. (Even if I store the invocation.)

Is there any other way?

Answer 1

If you are on Snow Leopard, you can use Blocks:

dispatch_async(dispatch_get_main_queue(), ^{
    [progressIndicator setDoubleValue: 50.0];
});