为什么需要保留 NSString 变量？
我的 .h 文件中有以下代码：
@interface Utils : NSObject {
NSString *dPath;
}
@property(nonatomic, retain) NSString *dPath;
在我的 .m 文件中：
NSArray *documentPaths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
dPath = [[documentPaths objectAtIndex:0] stringByAppendingPathComponent:kDatabaseName];
[dPath retain];
为什么我必须保留 dPath< /em> 如果它已经定义为（非原子，保留）？ 如果我不添加 [dPath keep];在其他函数中使用此变量时，我遇到一些奇怪的随机错误，并且应用程序崩溃。我想这是因为某些地方有一些自动释放，但我没有。
那么，（非原子，retain）到底在做什么呢？ [dPath keep] 真的有必要吗？或者我只是隐瞒了其他事情？
I have the following code in my .h file:
@interface Utils : NSObject {
NSString *dPath;
}
@property(nonatomic, retain) NSString *dPath;
And in my .m file:
NSArray *documentPaths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
dPath = [[documentPaths objectAtIndex:0] stringByAppendingPathComponent:kDatabaseName];
[dPath retain];
Why do I have to retain dPath if it's already defined as (nonatomic, retain)?
If I don't add the [dPath retain]; I get some strange, random errors and the application crashes when using this variable in other functions. I guess that's because of some autorelease somehere but I don't have any.
So, what is the (nonatomic, retain) doing anyway? Is it really necessary the [dPath retain]; or am I just hiding something else with that?
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因为代码没有调用
dPath属性的 setter 方法，它只是直接设置实例变量dPath：因此必须手动保留它。
如果像这样使用属性设置器（注意
self.），或者像这样（注意
setDPath:)：setter 会为您保留
NSString，因此您不必自己执行此操作。为了避免混淆，需要遵循的一个很好的小做法是在您的 ivar 名称后添加一个下划线以表明它是一个 ivar：
然后像这样综合您的属性，将其与您的不同名称的 ivar 关联起来：
然后修改您的
dealloc方法，以及直接引用实例变量的任何其他代码，请改为使用附加名称：Because the code isn't calling the
dPathproperty's setter method, it's just setting the instance variabledPathdirectly:So it has to be retained manually.
You will be able to (in fact you need to) omit the
retaincall if the property setter was used like this (notice theself.):or like this (notice the
setDPath:):The setter retains the
NSStringfor you so you don't have to do it yourself.A nice little practice to follow in order to avoid the confusion, is to affix an underscore to your ivar name to indicate it's an ivar:
Then synthesize your property like this, to associate it with your differently-named ivar:
Then modify your
deallocmethod, as well as any other code that directly references the instance var, to use the affixed name instead:尝试设置并获取它
try setting and getting it with
如果您想调用属性 setter 方法，该方法将调用保留，那么您需要编写：
将内容塞入变量中：
完全忽略此实例变量的属性。这就是为什么您最终需要手动进行保留。
If you want to call the property setter method, which will invoke the retain, then you want to write:
Jamming stuff into a variable with:
completely ignores the properties of this instance variable. Which is why you ended up needing to do the retain manually.