/**
     * 限制输入字符长度   中文算3字符，英文算1字符
     */
    InputFilter filter = new InputFilter() {
        final int maxLen = 21;
        @Override
        public CharSequence filter(CharSequence source, int start, int end, Spanned dest, int dstart, int dend) {
            // TODO Auto-generated method stub
            int dindex = 0;
            int count = 0;

            while (count <= maxLen && dindex < dest.length()) {
                char c = dest.charAt(dindex++);
                if (c < 128) {
                    count = count + 1;
                } else {
                    count = count + 3;
                }
            }

            if (count > maxLen) {
                return dest.subSequence(0, dindex - 1);
            }

            int sindex = 0;
            while (count <= maxLen && sindex < source.length()) {
                char c = source.charAt(sindex++);
                if (c < 128) {
                    count = count + 1;
                } else {
                    count = count + 3;
                }
            }

            if (count > maxLen) {
                sindex--;
            }

            return source.subSequence(0, sindex);
        }
    };
EditText editText=(EditText)findViewById(R.id.edit_text);
editText.setFilters(new InputFilter[]{filter});