EditText输入手机号自动带空格

在android开发过程中，经常会要求用户输入手机号，为了便于观看，我们都会已135 xxxx xxxx这种格式展示
通过下面的方法，直接输入格式化。
xml布局文件中写法如下：

<EditText
    android:id="@+id/editText"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:maxLength="13"
    android:inputType="numberSigned" />

代码中写法如下：

final EditText editText = (EditText) findViewById(R.id.editText);
        editText.addTextChangedListener(new TextWatcher() {
            @Override
            public void beforeTextChanged(CharSequence s, int start, int count, int after) {

            }

            @Override
            public void onTextChanged(CharSequence charSequence, int start, int before, int count) {
                if (charSequence == null || charSequence.length() == 0)
                    return;
                StringBuilder stringBuilder = new StringBuilder();
                for (int i = 0; i < charSequence.length(); i++) {
                    if (i != 3 && i != 8 && charSequence.charAt(i) == ' ') {
                        continue;
                    } else {
                        stringBuilder.append(charSequence.charAt(i));
                        if ((stringBuilder.length() == 4 || stringBuilder.length() == 9)
                                && stringBuilder.charAt(stringBuilder.length() - 1) != ' ') {
                            stringBuilder.insert(stringBuilder.length() - 1, ' ');
                        }
                    }
                }
                if (!stringBuilder.toString().equals(charSequence.toString())) {
                    int index = start + 1;
                    if (stringBuilder.charAt(start) == ' ') {
                        if (before == 0) {
                            index++;
                        } else {
                            index--;
                        }
                    } else {
                        if (before == 1) {
                            index--;
                        }
                    }
                    editText.setText(stringBuilder.toString());
                    editText.setSelection(index);
                }
            }

            @Override
            public void afterTextChanged(Editable s) {

            }
        });
    }