Android 格式化存储之Formatter

格式化存储相关的数值时，可以用 android.text.format.Formatter 。

Formatter.formatFileSize(Context context, long sizeBytes)

源码说明，在 Android O 后，存储单位的进制是 1000 ，Android N 之前单位进制是 1024 。

/**
     * Formats a content size to be in the form of bytes, kilobytes, megabytes, etc.
     *
     * 
As of O, the prefixes are used in their standard meanings in the SI system, so kB = 1000
     * bytes, MB = 1,000,000 bytes, etc.
     *
     * 
In {@link android.os.Build.VERSION_CODES#N} and earlier, powers of 1024 are
     * used instead, with KB = 1024 bytes, MB = 1,048,576 bytes, etc.
     *
     * 
If the context has a right-to-left locale, the returned string is wrapped in bidi
     * formatting characters to make sure it's displayed correctly if inserted inside a
     * right-to-left string. (This is useful in cases where the unit strings, like "MB", are
     * left-to-right, but the locale is right-to-left.)
     *
     * @param context Context to use to load the localized units
     * @param sizeBytes size value to be formatted, in bytes
     * @return formatted string with the number
     */
    public static String formatFileSize(@Nullable Context context, long sizeBytes) {
        return formatFileSize(context, sizeBytes, FLAG_SI_UNITS);
    }

它采用四舍五入，保留两位小数，自动补全 kB 、MB、GB 等单位。
示例，注释即是运行结果

	private void testFormatFileSize(){
        long size0 = 1000; // 1.00 kB
        long size1 = 1024; // 1.02 kB
        long size2 = 1000 * 1000; // 1.00 MB
        long size3 = 1000 * 1000 * 1000; // 1.00 GB
        long size4 = size3 + 30 * size2; // 1.03 GB
        long size5 = size3 + 519 * size2; //  1.52 GB
        String result0 = Formatter.formatFileSize(MainActivity.this, size0);
        String result1 = Formatter.formatFileSize(MainActivity.this, size1);
        String result2 = Formatter.formatFileSize(MainActivity.this, size2);
        String result3 = Formatter.formatFileSize(MainActivity.this, size3);
        String result4 = Formatter.formatFileSize(MainActivity.this, size4);
        String result5 = Formatter.formatFileSize(MainActivity.this, size5);
        Log.d("test" , "[MainActivity] -- formatFileSize -- result0 : " + result0);
        Log.d("test" , "[MainActivity] -- formatFileSize -- result1 : " + result1);
        Log.d("test" , "[MainActivity] -- formatFileSize -- result2 : " + result2);
        Log.d("test" , "[MainActivity] -- formatFileSize -- result3 : " + result3);
        Log.d("test" , "[MainActivity] -- formatFileSize -- result4 : " + result4);
        Log.d("test" , "[MainActivity] -- formatFileSize -- result5 : " + result5);
    }

Formatter.formatShortFileSize(Context context, long sizeBytes)

源码说明，

/**
     * Like {@link #formatFileSize}, but trying to generate shorter numbers
     * (showing fewer digits of precision).
     */
    public static String formatShortFileSize(@Nullable Context context, long sizeBytes) {
        if (context == null) {
            return "";
        }
        final BytesResult res = formatBytes(context.getResources(), sizeBytes,
                FLAG_SI_UNITS | FLAG_SHORTER);
        return bidiWrap(context, context.getString(com.android.internal.R.string.fileSizeSuffix,
                res.value, res.units));
    }

它采用四舍五入，保留一位小数，自动补全 kB 、MB、GB 等单位。
示例，注释即是运行结果

	private void testFormatShortFileSize(){
        long size0 = 1000; // 1.0 kB
        long size1 = 1024; // 1.0 kB
        long size2 = 1000 * 1000; // 1.0 MB
        long size3 = 1000 * 1000 * 1000; // 1.0 GB
        long size4 = size3 + 256 * size2; // 1.3 GB
        String result0 = Formatter.formatShortFileSize(MainActivity.this, size0);
        String result1 = Formatter.formatShortFileSize(MainActivity.this, size1);
        String result2 = Formatter.formatShortFileSize(MainActivity.this, size2);
        String result3 = Formatter.formatShortFileSize(MainActivity.this, size3);
        String result4 = Formatter.formatShortFileSize(MainActivity.this, size4);
        Log.d("test" , "[MainActivity] -- testFormatShortFileSize -- result0 : " + result0);
        Log.d("test" , "[MainActivity] -- testFormatShortFileSize -- result1 : " + result1);
        Log.d("test" , "[MainActivity] -- testFormatShortFileSize -- result2 : " + result2);
        Log.d("test" , "[MainActivity] -- testFormatShortFileSize -- result3 : " + result3);
        Log.d("test" , "[MainActivity] -- testFormatShortFileSize -- result4 : " + result4);
    }