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I had a problem where I was using performSelectorOnMainThread:... to update UI but was getting exceptions when an update occurred whilst the mouse was down for a user. Using the modes parameter of performSelectorOnMainThread:... doesn't work since even though NSTextView's mouseDown function runs the event loop in NSEventTrackingRunLoopMode?, the queuePeriodicEvent framework function gets called which runs the loop in NSDefaultRunLoopMode.
To workaround the problem, I've used the following code, i.e. basically sub-classed NSApplication and overridden sendEvent.
@interface NSObject (CSSafePerform)
- (void)safelyPerformSelectorOnMainThread:(SEL)selector
withObject:(id)arg;
@end
@interface NSApplication (CSSafePerform)
- (void)safelyPerformSelectorOnMainThread:(SEL)selector
target:(id)self
withObject:(id)arg;
@end
@interface CSApplication : NSApplication {
BOOL processingEvent;
NSMutableArray *performQueue;
}
@end
@implementation NSObject (CSSafePerform)
- (void)safelyPerformSelectorOnMainThread:(SEL)selector
withObject:(id)arg
{
NSAssert ([NSApp isKindOfClass:[CSApplication class]],
@"safelyPerformSelectorOnMainThread not supported");
[NSApp safelyPerformSelectorOnMainThread:selector
target:self
withObject:arg];
}
@end
@implementation CSApplication
typedef struct {
SEL selector;
id target;
id arg;
} PerformInfo;
- (void)performOnMainThread:(NSValue *)info
{
if (processingEvent) {
if (!performQueue)
performQueue = [[NSMutableArray alloc] init];
[performQueue addObject:info];
} else {
PerformInfo pi;
[info getValue:&pi];
[pi.target performSelector:pi.selector withObject:pi.arg];
[pi.target release];
[pi.arg release];
}
}
- (void)safelyPerformSelectorOnMainThread:(SEL)selector
target:(id)target
withObject:(id)arg
{
PerformInfo pi = (PerformInfo) { selector,
[target retain],
[arg retain] };
NSValue *v = [NSValue valueWithBytes:&pi
objCType:@encode (PerformInfo)];
[self performSelectorOnMainThread:@selector (performOnMainThread:)
withObject:v
waitUntilDone:NO];
}
- (void)sendEvent:(NSEvent *)anEvent
{
BOOL oldProcessingEvent = processingEvent;
processingEvent = YES;
@try {
[super sendEvent:anEvent];
} @finally {
if (!oldProcessingEvent) {
processingEvent = NO;
if (performQueue) {
NSEnumerator *e = [performQueue objectEnumerator];
NSValue *v;
[performQueue release];
performQueue = nil;
while ((v = [e nextObject]))
[self performOnMainThread:v];
}
}
}
}
@end
Chris Suter, Coriolis Systems
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