可以使用 NSMutableData 对象调用 +[NSData dataWithData:] 吗？
我执行以下操作将可变数据实例更改为不可变是否有问题？
NSMutableData *mutData = [[NSMutableData alloc] init];
//Giving some value to mutData
NSData *immutableData = [NSData dataWithData:mutData];
[mutData release];
Is it a problem for me to do the following to change a mutable data instance immutable?
NSMutableData *mutData = [[NSMutableData alloc] init];
//Giving some value to mutData
NSData *immutableData = [NSData dataWithData:mutData];
[mutData release];
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这完全没问题，实际上是 dataWithData: 的主要用途之一——创建可变对象的不可变副本。*
NSData也符合 < a href="http://developer.apple.com/library/mac/documentation/Cocoa/Reference/Foundation/Protocols/NSCopying_Protocol/" rel="noreferrer">NSCopying协议，**这意味着您可以改用[mutData copy]。不同之处在于dataWithData:返回一个不属于您的对象（它是自动释放的），而 每个内存管理规则，copy创建一个由您负责其内存的对象。dataWithData:与[[mutData copy] autorelease]效果相同。因此，您可以选择
dataWithData:或copy，具体取决于您对结果对象生命周期的要求。*这也适用于具有可变子类的其他类中的类似方法，例如，
+[NSArray arrayWithArray:]。**另请参阅“对象复制” 在核心能力指南中。
This is completely okay, and is in fact one of the primary uses of
dataWithData:-- to create an immutable copy of a mutable object.*NSDataalso conforms to theNSCopyingprotocol,** which means you could instead use[mutData copy]. The difference is thatdataWithData:returns an object you do not own (it is autoreleased), whereas per memory management rules,copycreates an object for whose memory you are responsible.dataWithData:is equivalent in effect to[[mutData copy] autorelease].So you can choose either
dataWithData:orcopy, dependent upon your requirements for the lifetime of the resulting object.*This also applies to similar methods in other classes which have a mutable subclass, e.g.,
+[NSArray arrayWithArray:].**See also "Object Copying" in the Core Competencies Guide.
不，这不是问题。
immutableData将使用mutData中的数据进行初始化。No it is not a problem.
immutableDatawill be initialized with the data inmutData.