用于将大小转换为人类可读字符串的 ObjC/Cocoa 类? [英] ObjC/Cocoa class for converting size to human-readable string?

问题描述

有没有一种简单的方法可以做类似的事情..

Is there a simple way to do something like..

[NSMagicDataConverter humanStringWithBytes:20000000]

...哪个会返回19.1MB"?

..which would return "19.1MB"?

推荐答案

以下是我对这个问题的看法:

Here's my own take on the problem:

enum {
    kUnitStringBinaryUnits     = 1 << 0,
    kUnitStringOSNativeUnits   = 1 << 1,
    kUnitStringLocalizedFormat = 1 << 2
};

NSString* unitStringFromBytes(double bytes, uint8_t flags){

    static const char units[] = { '', '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 , *printf does not.
    return [NSString stringWithFormat:@"%@ %cB", [formatter stringFromNumber: [NSNumber numberWithDouble: bytes]], units[exponent]];
}

默认情况下(如果 0 被传递给 flags)，它将输出 SI 单位(基数为 10).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 之前的为基数为 2，后豹得到基数).设置 kUnitStringLocalizedFormat 根据用户的当前区域设置格式化字符串.例如:

By default (if 0 is passed for flags), it will output SI units (base ten). You can set kUnitStringBinaryUnits to select binary (base two) units suitable for memory, or kUnitStringOSNativeUnits to have the unit type selected automatically based on OS version (pre-Leopard gets base two, post-Leopard gets base ten). Setting kUnitStringLocalizedFormat formats the string based on the user's current locale. For example:

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)

<小时>

这是操作系统原生单元所需的辅助函数:

---

Here's the helper function required for OS-native units:

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;
}

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