Android限制输入框10个汉字或20个字母

功能较少，直接看代码：

import android.text.InputFilter
import android.text.Spanned

/**
 * @author: Sid
 * @email: [email protected]
 * @date: 2018/5/31 17:18
 */
class ChineseLengthFilter(val length: Int) : InputFilter {

    override fun filter(source: CharSequence, start: Int, end: Int, dest: Spanned, dstart: Int, dend: Int): CharSequence {
        var len = calculateLength(dest)

        val builder = StringBuilder()
        if (len >= length) {
            return ""
        } else {
            for (c in source) {
                if (isChineseChar(c)) {
                    len += 2
                } else {
                    len++
                }
                builder.append(c)
                if (len >= length) {
                    break
                }
            }
        }
        return builder.toString().trim()
    }

    private fun isChineseChar(c: Char): Boolean {
        val ub = Character.UnicodeBlock.of(c)
        return (ub === Character.UnicodeBlock.CJK_UNIFIED_IDEOGRAPHS
                || ub === Character.UnicodeBlock.CJK_COMPATIBILITY_IDEOGRAPHS
                || ub === Character.UnicodeBlock.CJK_UNIFIED_IDEOGRAPHS_EXTENSION_A
                || ub === Character.UnicodeBlock.CJK_UNIFIED_IDEOGRAPHS_EXTENSION_B
                || ub === Character.UnicodeBlock.CJK_SYMBOLS_AND_PUNCTUATION
                || ub === Character.UnicodeBlock.HALFWIDTH_AND_FULLWIDTH_FORMS
                || ub === Character.UnicodeBlock.GENERAL_PUNCTUATION)
    }

    private fun calculateLength(source: Spanned): Int {
        var len = 0
        for (c in source) {
            if (isChineseChar(c)) {
                len += 2
            } else {
                len++
            }
        }
        return len
    }
}