I want to invoke a selector of a method that has the usual NSError** argument:

-(int) getItemsSince:(NSDate *)when dataSelector:(SEL)getDataSelector error:(NSError**)outError  {
        NSArray *data = nil;     if([service respondsToSelector:getDataSelector]) {
            data = [service performSelector:getDataSelector withObject:whenwithObject:outError];         // etc.

... which the compiler doesn't like:

warning: passing argument 3 of 'performSelector:withObject:withObject:' fromincompatible pointer type

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签出 ，这使您可以更灵活的方式的"performSelector"。

if ([service respondsToSelector:getDataSelector]) {
        NSArray *data;     NSInvocation *invocation = [NSInvocation invocationWithMethodSignature:         [service methodSignatureForSelector:getDataSelector]];     [invocation setTarget:delegate];     [invocation setSelector:getDataSelector];     // Note: Indexes 0 and 1 correspond to the implicit arguments self and _cmd,      // which are set using setTarget and setSelector.     [invocation setArgument:when atIndex:2];      [invocation setArgument:outError atIndex:3];     [invocation invoke];     [invocation getReturnValue:&data]; }

perform selector调用超过两个以上参数的方法

也可以把所有的参数放到字典里, 像NSNotification或者NSTimer的userinfo