[英]Strange issue with readonly properties for iVars in iOS
Here is what I have: 这是我有的:
@interface engine : NSObject
{
int test;
}
@property (nonatomic, readonly) int test;
When I try to assign a value(10) to iVar test within my own class (engine class), the debugger shows test = 10, and _test = 0. 当我尝试在我自己的类(引擎类)中为iVar测试分配值(10)时,调试器显示test = 10和_test = 0。
When I try to read from test, I get 0, I'm guessing i'm getting the value of_test. 当我尝试从测试中读取时,我得到0,我猜我得到了值of_test。
How do I make it work the way it is supposed to? 如何让它按照预期的方式工作? I want outside classes to have readonly access to "test", but within my class, I can assign and read values to/from "test"?
我希望外部类只能读取“test”,但在我的课程中,我可以为“test”分配和读取值吗?
Or what is wrong with this implementation? 或者这个实现有什么问题?
UPDATE:I do no syntesize as I use xcode 4.4 which automatially does it for you. 更新:我没有同步,因为我使用xcode 4.4,它自动为你做。 I assume the synthesize will use the same iVar name as the property.
我假设合成将使用相同的iVar名称作为属性。 Which is the default behaviour anyways if you do a normal synthesize.
如果进行正常的合成,这是默认行为。
Thanks. 谢谢。
It is hard to say without seeing your code, but I am guessing, that you are trying to do something like test=10
instead of self.test=10
. 很难说没有看到你的代码,但我猜,你正在尝试做一些像
test=10
而不是self.test=10
。 Depending on the version of ObjC/XCode you use and on a possible @synthesize
statement, you are accessing a (whereever defined) local variable, but not the property resp. 根据您使用的ObjC / XCode的版本以及可能的
@synthesize
语句,您正在访问(定义的)局部变量,但不访问属性resp。 it's iVar. 这是iVar。
EDIT 编辑
When you want to write a readonly property, you should use its iVar. 如果要编写只读属性,则应使用其iVar。 Eg, after
_test=10
both read accesses, self.test
and _test
(but not pure test
!) should provide the same value. 例如,后
_test=10
既读访问, self.test
和_test
(但不是纯test
!)应该提供相同的值。
You assume wrong. 你认为是错的。 The default implementation is to produce the property name with an under bar.
默认实现是使用下划线生成属性名称。 If you want a different name you will need to synthesize it yourself.
如果你想要一个不同的名字,你需要自己合成它。
Automatic synthesize creates an instance variable with a underscore prefix, so a property called test
generates a backing instance variable of _test
. 自动合成创建带有下划线前缀的实例变量,因此名为
test
的属性会生成_test
的后备实例变量。 So you have two instance variables; 所以你有两个实例变量;
test
, which isn't connected to the property, and _test
. test
,没有连接到属性, _test
。 If you write to the instance variable test
, it will not be reflected in _test
or the property's value. 如果您写入实例变量
test
,它将不会反映在_test
或属性的值中。
But more to the point, declaring the backing instance variable yourself is pointless. 但更重要的是,自己声明支持实例变量毫无意义。 It's just an extra code and unnecessary redundancy.
这只是一个额外的代码和不必要的冗余。 The
@property
line already contains type, name, whether it's read/write or read-only and a storage qualifier. @property
行已包含类型,名称,是读/写还是只读以及存储限定符。 Just skip declaring the backing instance variable yourself and use the one the compiler generates for you. 只需跳过自己声明支持实例变量并使用编译器为您生成的变量。
In Engine.h: 在Engine.h中:
@interface Engine : NSObject
@property (readonly, assign) NSInteger test;
- (void)doSomething;
@end
In Engine.m: 在Engine.m中:
@implementation Engine
- (void)doSomething {
_test++; // _test is created automatically by the compiler
}
@end
In other.m: 在other.m:
Engine *engine = [[Engine alloc] init];
NSLog(@"%d", engine.test); // 0
[engine doSomething];
NSLog(@"%d", engine.test); // 1
This all just works. 一切正常。 Don't add to it.
不要添加它。
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