如何解决NSTask调用 - [NSString fileSystemRepresentation]的参数

问题描述

似乎 NSTask 调用 - [NSString fileSystemRepresentation] 来编码每个参数的值。

在某些情况下，这可能会成为一个问题，因为 -fileSystemRepresentation unicode形式：例如，a-umlaut（ä）将编码为U + 0061（拉丁字母a）和U + 0308（组合diaeresis），而不是U + 00E4具有透析）。 -UTF8String 方法，另一方面，似乎做的相反。

我需要我的 NSTask 要使用组合表单编码的参数。如何解决这个问题？

解决方案

一个可能的解决方案是子类 NSString 并提供您自己的实现 -fileSystemRepresentation ，但不幸的是 NSString 是一个类集群，因此非常困难

但是，我们可以创建一个单独的类 作为 NSString ，但提供自己的 -fileSystemRepresentation 实现

，但是，如果 NSTask 使用参数对象的类标识执行任何操作，则会产生问题。目前我没有证据证明是这种情况 - 此解决方法似乎工作完美。

标题：

  // MYTaskArgument.h 
 
 @interface MYTaskArgument：NSObject 
 +（instancetype）taskArgumentWithString：（NSString *）str;实施：
 
 
        pre>  // MYTaskArgument.m 
 
 @interface MYTaskArgument（）
 @property（copy）NSString * string; 
 @end 
 
 @implementation MYTaskArgument 
 
 +（instancetype）taskArgumentWithString：（NSString *）str {
 MYTaskArgument * ret = [[MYTaskArgument alloc]在里面]; 
 ret.string = str; 
 return ret; 
} 
 
  - （const char *）fileSystemRepresentation {
 return self.string.UTF8String; 
} 
 
  - （id）forwardingTargetForSelector：（SEL）aSelector {
 return self.string; 
} 
 
 @end 
  




It seems that NSTask calls -[NSString fileSystemRepresentation] to encode values for each of the arguments you give it.

This can become a problem in some situations due to the fact that -fileSystemRepresentation encodes using decomposed unicode forms: for example, the a-umlaut (ä) would be encoded as U+0061 (Latin small letter a) and U+0308 (Combining diaeresis), as opposed to U+00E4 (Latin small letter a with diaeresis). The -UTF8String method, on the other hand, seems to do the opposite.

I need my NSTask arguments to be encoded using composed forms. How do I work around this issue?

解决方案

A possible solution would be to subclass NSString and provide your own implementation of -fileSystemRepresentation, but unfortunately NSString is a class cluster and thus very difficult to subclass (which is also discouraged by Apple's documentation).

However, we can create a separate class that poses as an NSString, but provides its own implementation of -fileSystemRepresentation.

This can, however, create problems if NSTask does anything with the class identity of the argument objects. Currently I have no evidence that this is the case — this workaround seems to work perfectly.

Header:

// MYTaskArgument.h

@interface MYTaskArgument : NSObject
+ (instancetype) taskArgumentWithString:(NSString *)str;
@end

Implementation:

// MYTaskArgument.m

@interface MYTaskArgument ()
@property(copy) NSString *string;
@end

@implementation MYTaskArgument

+ (instancetype) taskArgumentWithString:(NSString *)str {
    MYTaskArgument *ret = [[MYTaskArgument alloc] init];
    ret.string = str;
    return ret;
}

- (const char *) fileSystemRepresentation {
    return self.string.UTF8String;
}

- (id) forwardingTargetForSelector:(SEL)aSelector {
    return self.string;
}

@end

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