afterTextChanged方法。

private final int MAX_CHAR_NUM = 20;

   mSearchEditText.addTextChangedListener(new SimpleTextWatcher() {
            @Override
            public void afterTextChanged(Editable s) {

                int charSequenceCount = countChineseChar(s);

                if (s.length() + charSequenceCount > MAX_CHAR_NUM) {
                    mSearchEditText.setText(s.subSequence(0, s.length() - 1));
                    return;
                }
        });

//計算中文字元

 /**
     * 計算中文字元
     *
     * @param sequence
     * @return
     */
    private int countChineseChar(CharSequence sequence) {

        if (TextUtils.isEmpty(sequence)) {
            return 0;
        }
        int charNum = 0;
        for (int i = 0; i < sequence.length(); i++) {
            char word = sequence.charAt(i);
            if (StringUtils.isChineseChar(word)) {//中文
                charNum++;
            }
        }
        return charNum;
    }

/**

     * 判斷是否是中文
     * @param c
     * @return
     */
    public static boolean isChineseChar(char c) {
        Character.UnicodeBlock ub = Character.UnicodeBlock.of(c);
        if (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) {
            return true;
        }
        return false;
    }