name_tv = (EditText) findViewById( R.id.name_tv );

         name_tv.addTextChangedListener(new TextWatcher() {

             @Override

             public void beforeTextChanged(CharSequence s, int start, int count, int after) {

             }

             @Override

             public void onTextChanged(CharSequence s, int start, int before, int count) {

             }

             @Override

             public void afterTextChanged(Editable s) {

                 String string = s.toString().trim();

                 //限定输入框最多输入18个字节

                 int inputLength = string.length();

                 int byteLength = string.getBytes().length;

                 if (byteLength >= 18) {

                     name_tv.setFilters(new InputFilter[]{new InputFilter.LengthFilter(inputLength)});

                 } else {

                     name_tv.setFilters(new InputFilter[]{new InputFilter.LengthFilter(18)});

                 }

                 name_tv.setSelection(name_tv.getText().toString().length());

             }

         });