运行 performSelector:在返回双精度值而不是 id 的对象上 [英] Running performSelector: on an object that returns a double, not id
问题描述
如何在对象上运行任意选择器,其返回值为双精度值?例如,我有 obj A,它有方法 -(double)blah;
How can I run an arbitrary selector on an object, the return of which is a double? For example, I have obj A, which has method -(double)blah;
我该怎么做double res = [obj performSelector:@selector(blah)];
?performSelector 返回一个 id
类型的对象,所以我应该从 id 转换为 NSInteger 到 double - 这会失去精度吗?
How can I do double res = [obj performSelector:@selector(blah)];
? performSelector returns an id
type object, so should I cast from id to NSInteger to double - that will lose precision?
另外,我不想想使用 obj 的 methodSignatureForSelector
(意思是,没有 NSMethodSignature
和没有 NSInvocation
) 因为它在运行时会消耗大量 CPU.
Also, I do not want to use the obj's methodSignatureForSelector
(meaning, no NSMethodSignature
and no NSInvocation
) because it is a huge CPU drain at run-time.
推荐答案
使用最少的内存(valueForKey:使用两个临时对象)并且 msgSend 方法不起作用.
Uses least memory (valueForKey: uses two temporary objects) and the msgSend method doesn't work.
IMP myImp1 = [obj methodForSelector:@selector(getDouble)];
double aDouble1 = ((double (*) (id,SEL))myImp1)(obj,@selector(getDouble));
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