performSelector的返回值:

Question

performSelector的返回值是什么:如果我传递一个返回基本类型(在对象上)的选择器,例如NSDateComponents上的'week'(将返回一个int)？

Answer 1

使用NSInvocation返回float的示例:

SEL selector = NSSelectorFromString(@"someSelector");
if ([someInstance respondsToSelector:selector]) {
    NSInvocation *invocation = [NSInvocation invocationWithMethodSignature:
                                [[someInstance class] instanceMethodSignatureForSelector:selector]];
    [invocation setSelector:selector];
    [invocation setTarget:someInstance];
    [invocation invoke];
    float returnValue;
    [invocation getReturnValue:&returnValue];
    NSLog(@"Returned %f", returnValue);
}

Answer 2

我认为你无法从performSelector获取返回值.你应该调查一下NSInvocation.

Answer 3

老问题新答案~

有一种更简洁的方法可以从中获取返回值 performSelector

NSInvocationOperation *invo = [[NSInvocationOperation alloc] initWithTarget:self selector:@selector(height) object:nil];
[invo start];
CGFloat f = 0;
[invo.result getValue:&f];
NSLog(@"operation: %@", @(f));

其中

- (CGFloat)height {
    return 42;
}

输出

2017-03-28 16:22:22.378 redpacket[46656:7361082] operation: 42