思路：中文占一個(gè)長(zhǎng)度，英文占0.5個(gè)長(zhǎng)度（同時(shí)符號(hào)區(qū)分中英文）。
步驟：
1.EditText添加監(jiān)聽(tīng)是事件
2.在onTextChanged()方法中計(jì)算長(zhǎng)度
具體代碼如下：

editText.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) {
                int contentlength = (int) Math.round(contentLength(s));
                if (contentlength>30){//截取,最大長(zhǎng)度為30，超過(guò)30截取
                    CharSequence charSequence=s.subSequence(0,start);
                    editText.setText(charSequence);
                    Editable editable =  editText.getText();
                    int selEndIndex = editable.length();
                    Selection.setSelection(editable, selEndIndex);//光標(biāo)移動(dòng)到末尾
                }
            }

            @Override
            public void afterTextChanged(Editable s) {
            }
        });

計(jì)算長(zhǎng)度

    public double contentLength(CharSequence str) {
        double len = 0;
        for (int i = 0; i < str.length(); i++) {
            int temp = str.charAt(i);
            if (temp < 127 && temp > 0) {
                len += 0.5;
            } else {
                len++;
            }
        }
        return len;
    }