示例方法
- (void)printStr:(NSString*)str{
NSLog(@"printStr %@",str);
}
1. 直接调用
[self printStr:@"hello world 1"];
2. performSelector
[self performSelector:@selector(printStr:) withObject:@"hello world 2"];
3.NSMethodSignature & NSInvocation
- (id)performSelector:(SEL)selector byDelegate:(id<EWLiveMessageProcessorDelegate>) delegate withObjects:(NSArray *)objects
{
#方法签名(方法的描述)
NSMethodSignature *signature = [[delegate class] instanceMethodSignatureForSelector:selector];
if (signature == nil) {
#可以抛出异常也可以不操作。
return nil;
}
# NSInvocation : 利用一个NSInvocation对象包装一次方法调用（方法调用者、方法名、方法参数、方法返回值）
NSInvocation *invocation = [NSInvocation invocationWithMethodSignature:signature];
invocation.target = delegate;
invocation.selector = selector;
#设置参数
NSInteger paramsCount = signature.numberOfArguments - 2; // 除self、_cmd以外的参数个数
paramsCount = MIN(paramsCount, objects.count);
for (NSInteger i = 0; i < paramsCount; i++) {
id object = objects[i];
if ([object isKindOfClass:[NSNull class]]) continue;
[invocation setArgument:&object atIndex:i + 2];
}
# 调用方法
[invocation invoke];
#获取返回值
id returnValue = nil;
if (signature.methodReturnLength) { // 有返回值类型，才去获得返回值
[invocation getReturnValue:&returnValue];
}
return returnValue;
}
4. objc_msgSend
SEL sel = NSSelectorFromString(@"printWithString:withNum:withArray:");
#带参数无返回值
((void (*) (id, SEL, NSString *, NSNumber *, NSArray *)) objc_msgSend) (self, sel, str, num, arr);
#带参数及返回值
((int (*)(id, SEL, NSString *, int))objc_msgSend)( (id)msg,
@selector(hasArguments:andReturnValue:),
@"参数1",
2016);
