Objective-c – How to pass @selector as a parameter

iphoneobjective cselector

For the method:

[NSThread detachNewThreadSelector:@selector(method:) toTarget:self withObject:(id)SELECTOR];

How do I pass in a @selector? I tried casting it to (id) to make it compile, but it crashes in runtime.

More specifically, I have a method like this:

[NSThread detachNewThreadSelector:@selector(method2:) toTarget:self withObject:selector];   

It crashes. How do I pass in the selector without crashing, so that the new thread can call the selector when the thread is ready?

Best Answer

The problem here isn't passing a selector to a method, per se, but passing a selector where an object is expected. To pass a non-object value as an object, you can use NSValue. In this case, you'll need to create a method that accepts an NSValue and retrieves the appropriate selector. Here's an example implementation:

@implementation Thing
- (void)method:(SEL)selector {
    // Do something

- (void)methodWithSelectorValue:(NSValue *)value {
    SEL selector;

    // Guard against buffer overflow
    if (strcmp([value objCType], @encode(SEL)) == 0) {
        [value getValue:&selector];
        [self method:selector];

- (void)otherMethodShownInYourExample {
    SEL selector = @selector(something);
    NSValue *selectorAsValue = [NSValue valueWithBytes:&selector objCType:@encode(SEL)];
    [NSThread detachNewThreadSelector:@selector(methodWithSelectorValue:) toTarget:self withObject:selectorAsValue];