Question

我有一个NSString，在我的生命中，我无法弄清楚如何remove spaces然后选择它last 30 characters。

错误如：

3/5/13 3:38:30 PM *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[__NSCFType UTF8String]: unrecognized selector sent to instance 0x160bf20'

或

3/5/13 3:30:51 PM *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[__NSCFType length]: unrecognized selector sent to instance 0x160bf20'

我不明白这些错误。

代码：

NSString* m = (NSString*)CFDictionaryGetValue(diskDesc, kDADiskDescriptionVolumeUUIDKey);
[m stringByReplacingOccurrencesOfString:@" " withString:@""]    
NSString *newString = [m substringToIndex:[m length]-30];

另一个更新：

NSString * m = (NSString*)CFDictionaryGetValue(diskDesc, kDADiskDescriptionDeviceModelKey);
NSString * v = (NSString*)CFDictionaryGetValue(diskDesc, kDADiskDescriptionVolumeUUIDKey);

if(m)
{
    m = [m stringByReplacingOccurrencesOfString:@" " withString:@""];
}

if(v)
{
    if([v length] > 30)
    {
        NSString *newString = [v substringToIndex:[v length]-30];
    }
}

Answer 1

看起来是错误检查的绝佳机会。像这样：

NSString * m = (NSString*)CFDictionaryGetValue(diskDesc, kDADiskDescriptionDeviceModelKey);
if(m)
{
    m = [m stringByReplacingOccurrencesOfString:@" " withString:@""]
    if([m length] > 30)
    {
        NSString *newString = [m substringToIndex:[m length]-30];
    } else {
        NSLog( @"m isn't even 30 characters");
    }
} else {
    NSLog( @"I didn't get anything useful from my call to CFDictionaryGetValue");
}

Answer 2

您应该记下DADisk.h头文件中的文档，该文件指定字典为特定键保存的结果类型：

extern const CFStringRef kDADiskDescriptionVolumeUUIDKey;      /* ( CFUUID       ) */

extern const CFStringRef kDADiskDescriptionDeviceModelKey;     /* ( CFString     ) */

所有密钥本身都是NSString / CFString s，但是当您向字典询问该密钥的值时，没有任何内容表明它必须是字符串。右括号中的值显示该键的值的类型。

要获取CFUUID键所包含的kDADiskDescriptionVolumeUUIDKey的字符串表示形式，可以使用CFUUIDCreateString（）：

CFUUIDRef UUID = (CFUUIDRef)[(NSDictionary *)diskDesc
               objectForKey:(id)kDADiskDescriptionVolumeUUIDKey];

NSString *UUIDString = [(id)CFUUIDCreateString(NULL, UUID) autorelease];

此外，删除kDADiskDescriptionDeviceModelKey上的无关空格的代码可能如下：

NSString *deviceModel = [(NSDictionary *)diskDesc
              objectForKey:(id)kDADiskDescriptionDeviceModelKey];

NSLog(@"deviceModel == '%@'", deviceModel);

NSCharacterSet *whitespaceCharacterSet = [NSCharacterSet
                                  whitespaceAndNewlineCharacterSet];

deviceModel = [deviceModel stringByTrimmingCharactersInSet:whitespaceCharacterSet];

NSLog(@"deviceModel == '%@'", deviceModel);

该代码为我记录了以下内容：

diskArbitrationFinagler[] deviceModel == 'WDC WD6400AAKS-41H2B0                   '
diskArbitrationFinagler[] deviceModel == 'WDC WD6400AAKS-41H2B0'

您的stringByReplacingOccurrencesOfString:会错误地删除WDC和WD64....之间的空格。

从NSString中删除最后一个字符

2 个答案: