为什么我不能使用从Objective-C对象到Swift属性的KVC? [英] Why can I not use KVC from an Objective-C object to a Swift Property?
问题描述
我的团队决定应该快速编写新文件,我发现在Objective-C对象中使用KVC在Swift对象上设置属性是一个奇怪的问题.
My team has decided that new files should be written in swift, and I am seeing an odd problem with using KVC in an Objective-C object to set a property on a Swift object.
我的Objective-C设置如下属性:[textObject setValue:0.0 forKey:@"fontSize"]
My Objective-C sets a property like so: [textObject setValue:0.0 forKey:@"fontSize"]
我的Swift对象(textObject
)为此属性提供了一个自定义的setter/getter.
My Swift object (textObject
) has a custom setter/getter for this property.
var fontSize: CGFloat? {
get {
return internalTextGraphic?.fontSize
}
set {
internalTextGraphic?.fontSize = newValue
}
}
但是,如果我在set
中设置了一个断点,它将永远不会被击中.
However, if I set a breakpoint in the set
, it never gets hit.
我有一些Objective-C对象也得到了同样的调用,我只是实现了
-setFontSize
,并且执行正确进入.
I have Objective-C objects that also get this same call, and I just implement
-setFontSize
, and the execution enters properly.
为什么我似乎无法通过-setValueForKey
进入我的set
方法?
我100%确认textObject
存在并且是正确的类型.
Why can't I seem to get into my set
method through -setValueForKey
?
I have 100% confirmed the textObject
is exists and is the correct type.
编辑:
Martin R是正确的,我不得不将类型设为非可选.这是我的工作代码:
EDIT:
Martin R is correct, I had to make the type a non-optional. This is my working code:
var fontSize: CGFloat {
get {
var retFontSize: CGFloat = 0.0
if let fontSize = internalTextGraphic?.fontSize {
retFontSize = fontSize
}
return retFontSize
}
set {
if let textGraphic = internalTextGraphic {
textGraphic.fontSize = newValue
}
}
}
推荐答案
原因是Swift可选结构或枚举(在您的情况下为CGFloat?
)
在Objective-C中无法表示(并且您不会看到该属性
在生成的"Project-Swift.h"
头文件中).这变得更加明显
如果您标记该物业
@objc
明确地显示,然后您将收到错误消息
The reason is that a Swift optional struct or enum (in your case CGFloat?
)
is not representable in Objective-C (and you won't see that property
in the generated "Project-Swift.h"
header file). That becomes more obvious
if you mark the property
explicitly with @objc
, then you'll get the error message
error: property cannot be marked @objc because its type cannot be represented in Objective-C
如果将属性类型更改为非可选的CGFloat
然后KVC会按预期工作.它也可以与可选的
类类型,例如NSNumber?
.
If you change the property type to the non-optional CGFloat
then KVC works as expected. It would also work with an optional
class type, such as NSNumber?
.
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