有没有一种简单的方法可以做...
[NSMagicDataConverter humanStringWithBytes:20000000]
..会返回“19.1MB”？
答案 0 :(得分：103)
从OS X 10.8和iOS 6开始，您可以使用 NSByteCountFormatter 。
您的示例如下所示：
[NSByteCountFormatter stringFromByteCount:20000000 countStyle:NSByteCountFormatterCountStyleFile];
答案 1 :(得分：22)
我会把它变成一个NSFormatter子类。
#import <Foundation/Foundation.h>
@interface SOFileSizeFormatter : NSNumberFormatter
{
@private
BOOL useBaseTenUnits;
}
/** Flag signaling whether to calculate file size in binary units (1024) or base ten units (1000). Default is binary units. */
@property (nonatomic, readwrite, assign, getter=isUsingBaseTenUnits) BOOL useBaseTenUnits;
@end
static const char sUnits[] = { '\0', 'K', 'M', 'G', 'T', 'P', 'E', 'Z', 'Y' };
static int sMaxUnits = sizeof sUnits - 1;
@implementation SOFileSizeFormatter
@synthesize useBaseTenUnits;
- (NSString *) stringFromNumber:(NSNumber *)number
{
int multiplier = useBaseTenUnits ? 1000 : 1024;
int exponent = 0;
double bytes = [number doubleValue];
while ((bytes >= multiplier) && (exponent < sMaxUnits)) {
bytes /= multiplier;
exponent++;
}
return [NSString stringWithFormat:@"%@ %cB", [super stringFromNumber: [NSNumber numberWithDouble: bytes]], sUnits[exponent]];
}
@end
用法：
NSString *path = ...; // path to a file of 1,500,000 bytes
NSString *sizeString = nil;
NSNumber *sizeAttrib = [[[NSFileManager defaultManager] attributesOfItemAtPath:path error:NULL]objectForKey:NSFileSize];
SOFileSizeFormatter *sizeFormatter = [[[SOFileSizeFormatter alloc] init] autorelease];
[sizeFormatter setMaximumFractionDigits:2];
sizeString = [sizeFormatter stringFromNumber:sizeAttrib];
// sizeString ==> @"1.43 MB"
[sizeFormatter setUseBaseTenUnits:YES];
sizeString = [sizeFormatter stringFromNumber:sizeAttrib];
// sizeString ==> @"1.5 MB"
答案 2 :(得分：18)
这是我对问题的看法：
enum {
kUnitStringBinaryUnits = 1 << 0,
kUnitStringOSNativeUnits = 1 << 1,
kUnitStringLocalizedFormat = 1 << 2
};
NSString* unitStringFromBytes(double bytes, uint8_t flags){
static const char units[] = { '\0', 'k', 'M', 'G', 'T', 'P', 'E', 'Z', 'Y' };
static int maxUnits = sizeof units - 1;
int multiplier = (flags & kUnitStringOSNativeUnits && !leopardOrGreater() || flags & kUnitStringBinaryUnits) ? 1024 : 1000;
int exponent = 0;
while (bytes >= multiplier && exponent < maxUnits) {
bytes /= multiplier;
exponent++;
}
NSNumberFormatter* formatter = [[[NSNumberFormatter alloc] init] autorelease];
[formatter setMaximumFractionDigits:2];
if (flags & kUnitStringLocalizedFormat) {
[formatter setNumberStyle: NSNumberFormatterDecimalStyle];
}
// Beware of reusing this format string. -[NSString stringWithFormat] ignores \0, *printf does not.
return [NSString stringWithFormat:@"%@ %cB", [formatter stringFromNumber: [NSNumber numberWithDouble: bytes]], units[exponent]];
}
默认情况下（如果为0传递flags），它将输出SI单位（十进制）。您可以设置kUnitStringBinaryUnits以选择适合内存的二进制（基数为2）单位，或kUnitStringOSNativeUnits以根据操作系统版本自动选择单位类型（Leopard之前获得基数2，后豹获得基数十）。设置kUnitStringLocalizedFormat会根据用户的当前区域设置格式化字符串。例如：
unitStringFromBytes(1073741824, 0); // → "1.07 GB"
unitStringFromBytes(1073741824, kUnitStringBinaryUnits); // → "1 GB"
unitStringFromBytes(1073741824, kUnitStringOSNativeUnits | kUnitStringLocalizedFormat); // → "1.07 GB" (In Mac OS 10.6)
unitStringFromBytes(12345678901234567890123456789, kUnitStringOSNativeUnits | kUnitStringLocalizedFormat); // → "12,345.68 YB" (In Mac OS 10.6, in the US)
unitStringFromBytes(12345678901234567890123456789, kUnitStringOSNativeUnits | kUnitStringLocalizedFormat); // → "12.345,68 YB" (In Mac OS 10.6, in Spain)
这是OS本机单元所需的辅助函数：
BOOL leopardOrGreater(){
static BOOL alreadyComputedOS = NO;
static BOOL leopardOrGreater = NO;
if (!alreadyComputedOS) {
SInt32 majorVersion, minorVersion;
Gestalt(gestaltSystemVersionMajor, &majorVersion);
Gestalt(gestaltSystemVersionMinor, &minorVersion);
leopardOrGreater = ((majorVersion == 10 && minorVersion >= 5) || majorVersion > 10);
alreadyComputedOS = YES;
}
return leopardOrGreater;
}
答案 3 :(得分：6)
NSString *stringFromFileSize(NSInteger theSize)
{
/*
From http://snippets.dzone.com/posts/show/3038 with slight modification
*/
float floatSize = theSize;
if (theSize<1023)
return([NSString stringWithFormat:@"%i bytes",theSize]);
floatSize = floatSize / 1024;
if (floatSize<1023)
return([NSString stringWithFormat:@"%1.1f KB",floatSize]);
floatSize = floatSize / 1024;
if (floatSize<1023)
return([NSString stringWithFormat:@"%1.1f MB",floatSize]);
floatSize = floatSize / 1024;
return([NSString stringWithFormat:@"%1.1f GB",floatSize]);
}
答案 4 :(得分：6)
这是一个更像Objective C的函数（使用NSNumber，NSArray，NSStirng等......）进行这种转换。
这是基于Sidnicious的答案，所以非常感谢那里的最初工作。也基于维基百科文章。
通常使用它：[HumanReadableDataSizeHelper humanReadableSizeFromBytes:[NSNumber numberWithDouble:doubleValue]]。
但是，看起来您希望SI单位具有1024倍数，因此您可以像这样使用它：[HumanReadableDataSizeHelper humanReadableSizeFromBytes:[NSNumber numberWithDouble:doubleValue] useSiPrefixes:YES useSiMultiplier:NO]
我默认为二进制前缀（ki，Mi）的原因是因为它们似乎是用于计算机上数据大小的最合适的单位前缀。您请求的是SI单位前缀，但使用1024的乘数，技术上不正确。虽然我会注意到1024的倍数的SI前缀是相当常见的，并且二进制前缀不被广泛接受（根据维基百科）。
HumanReadableDataSizeHelper.h
@interface HumanReadableDataSizeHelper : NSObject
/**
@brief Produces a string containing the largest appropriate units and the new fractional value.
@param sizeInBytes The value to convert in bytes.
This function converts the bytes value to a value in the greatest units that produces a value >= 1 and returns the new value and units as a string.
The magnitude multiplier used is 1024 and the prefixes used are the binary prefixes (ki, Mi, ...).
*/
+ (NSString *)humanReadableSizeFromBytes:(NSNumber *)sizeInBytes;
/**
@brief Produces a string containing the largest appropriate units and the new fractional value.
@param sizeInBytes The value to convert in bytes.
@param useSiPrefixes Controls what prefix-set is used.
@param useSiMultiplier Controls what magnitude multiplier is used.
This function converts the bytes value to a value in the greatest units that produces a value >= 1 and returns the new value and units as a string.
When useSiPrefixes is true, the prefixes used are the SI unit prefixes (k, M, ...).
When useSiPrefixes is false, the prefixes used are the binary prefixes (ki, Mi, ...).
When useSiMultiplier is true, the magnitude multiplier used is 1000
When useSiMultiplier is false, the magnitude multiplier used is 1024.
*/
+ (NSString *)humanReadableSizeFromBytes:(NSNumber *)sizeInBytes useSiPrefixes:(BOOL)useSiPrefixes useSiMultiplier:(BOOL)useSiMultiplier;
@end
HumanReadableDataSizeHelper.m
@implementation HumanReadableDataSizeHelper
+ (NSString *)humanReadableSizeFromBytes:(NSNumber *)sizeInBytes
{
return [self humanReadableSizeFromBytes:sizeInBytes useSiPrefixes:NO useSiMultiplier:NO];
}
+ (NSString *)humanReadableSizeFromBytes:(NSNumber *)sizeInBytes useSiPrefixes:(BOOL)useSiPrefixes useSiMultiplier:(BOOL)useSiMultiplier
{
NSString *unitSymbol = @"B";
NSInteger multiplier;
NSArray *prefixes;
if (useSiPrefixes)
{
/* SI prefixes
http://en.wikipedia.org/wiki/Kilo-
kilobyte (kB) 10^3
megabyte (MB) 10^6
gigabyte (GB) 10^9
terabyte (TB) 10^12
petabyte (PB) 10^15
exabyte (EB) 10^18
zettabyte (ZB) 10^21
yottabyte (YB) 10^24
*/
prefixes = [NSArray arrayWithObjects: @"", @"k", @"M", @"G", @"T", @"P", @"E", @"Z", @"Y", nil];
}
else
{
/* Binary prefixes
http://en.wikipedia.org/wiki/Binary_prefix
kibibyte (KiB) 2^10 = 1.024 * 10^3
mebibyte (MiB) 2^20 ≈ 1.049 * 10^6
gibibyte (GiB) 2^30 ≈ 1.074 * 10^9
tebibyte (TiB) 2^40 ≈ 1.100 * 10^12
pebibyte (PiB) 2^50 ≈ 1.126 * 10^15
exbibyte (EiB) 2^60 ≈ 1.153 * 10^18
zebibyte (ZiB) 2^70 ≈ 1.181 * 10^21
yobibyte (YiB) 2^80 ≈ 1.209 * 10^24
*/
prefixes = [NSArray arrayWithObjects: @"", @"ki", @"Mi", @"Gi", @"Ti", @"Pi", @"Ei", @"Zi", @"Yi", nil];
}
if (useSiMultiplier)
{
multiplier = 1000;
}
else
{
multiplier = 1024;
}
NSInteger exponent = 0;
double size = [sizeInBytes doubleValue];
while ( (size >= multiplier) && (exponent < [prefixes count]) )
{
size /= multiplier;
exponent++;
}
NSNumberFormatter* formatter = [[[NSNumberFormatter alloc] init] autorelease];
[formatter setMaximumFractionDigits:2];
[formatter setNumberStyle:NSNumberFormatterDecimalStyle]; // Uses localized number formats.
NSString *sizeInUnits = [formatter stringFromNumber:[NSNumber numberWithDouble:size]];
return [NSString stringWithFormat:@"%@ %@%@", sizeInUnits, [prefixes objectAtIndex:exponent], unitSymbol];
}
@end
答案 5 :(得分：2)
您可以使用 FormatterKit 及其TTTUnitOfInformationFormatter类：
https://github.com/mattt/FormatterKit
它也可以通过CocoaPods获得：
pod 'FormatterKit', '~> 1.1.1'
答案 6 :(得分：1)
- (id)transformedValue:(id)value
{
double convertedValue = [value doubleValue];
int multiplyFactor = 0;
NSArray *tokens = @[@"bytes",@"KB",@"MB",@"GB",@"TB"];
while (convertedValue > 1024) {
convertedValue /= 1024;
multiplyFactor++;
}
return [NSString stringWithFormat:@"%4.2f %@",convertedValue, tokens[multiplyFactor]];
}
答案 7 :(得分：0)
我知道问题是针对Obj C的，但如果有人在寻找一个快速版本：
public static func fileSizeDisplay(fromBytes:Int) -> String {
let display = ["bytes","KB","MB","GB","TB","PB"]
var value:Double = Double(fromBytes)
var type = 0
while (value > 1024){
value /= 1024
type = type + 1
}
return "\(String(format:"%g", value)) \(display[type])"
}