在Android开发中怎么实现一个自定义输入法功能

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
  android:layout_width="match_parent"
  android:layout_height="match_parent">
  <!--前两个EditText均使用自定义的输入法-->
  <EditText
    android:id="@+id/input_password"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:layout_margin="8dp"
    android:hint="one password"
    android:layout_alignParentTop="true"
    android:inputType="textPassword" />
  <EditText
    android:id="@+id/input_password2"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:layout_below="@+id/input_password"
    android:layout_margin="8dp"
    android:hint="another password"
    android:inputType="textPassword" />
  <!--这个EditText使用默认的输入法-->
  <EditText
    android:id="@+id/input_normal_text"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:layout_below="@+id/input_password2"
    android:layout_margin="8dp"
    android:hint="normal text" />
  <android.inputmethodservice.KeyboardView
    android:id="@+id/keyboardview"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:layout_alignParentBottom="true"
    android:layout_centerHorizontal="true"
    android:focusable="true"
    android:focusableInTouchMode="true"
    android:visibility="gone" />
</RelativeLayout>

<&#63;xml version="1.0" encoding="utf-8"&#63;>
<Keyboard xmlns:android="http://schemas.android.com/apk/res/android"
  android:keyWidth="25%p"
  android:keyHeight="10%p">
  <Row>
    <Key
      android:codes="55"
      android:keyLabel="7"
      android:keyEdgeFlags="left" />
    <Key
      android:codes="56"
      android:keyLabel="8" />
    <Key
      android:codes="57"
      android:keyLabel="9" />
    <!--删除按键长按时连续响应-->
    <Key
      android:codes="60001"
      android:keyLabel="DEL"
      android:isRepeatable="true" />
  </Row>
  <Row>
    <Key
      android:codes="52"
      android:keyLabel="4"
      android:keyEdgeFlags="left" />
    <Key
      android:codes="53"
      android:keyLabel="5" />
    <Key
      android:codes="54"
      android:keyLabel="6" />
    <Key
      android:codes="48"
      android:keyLabel="0" />
  </Row>
  <Row>
    <Key
      android:codes="49"
      android:keyLabel="1"
      android:keyEdgeFlags="left" />
    <Key
      android:codes="50"
      android:keyLabel="2" />
    <Key
      android:codes="51"
      android:keyLabel="3" />
    <Key
      android:codes="60002"
      android:keyLabel="Cancel" />
  </Row>
</Keyboard>

public class KeyboardBuilder {
  private static final String TAG = "KeyboardBuilder";
  private Activity mActivity;
  private KeyboardView mKeyboardView;
  public KeyboardBuilder(Activity ac, KeyboardView keyboardView, int keyBoardXmlResId) {
    mActivity = ac;
    mKeyboardView = keyboardView;
    Keyboard mKeyboard = new Keyboard(mActivity, keyBoardXmlResId);
    // Attach the keyboard to the view
    mKeyboardView.setKeyboard(mKeyboard);
    // Do not show the preview balloons
    mKeyboardView.setPreviewEnabled(false);
    KeyboardView.OnKeyboardActionListener keyboardListener = new KeyboardView.OnKeyboardActionListener() {
      @Override
      public void onKey(int primaryCode, int[] keyCodes) {
        // Get the EditText and its Editable
        View focusCurrent = mActivity.getWindow().getCurrentFocus();
        if (focusCurrent == null || !(focusCurrent instanceof EditText)) {
          return;
        }
        EditText edittext = (EditText) focusCurrent;
        Editable editable = edittext.getText();
        int start = edittext.getSelectionStart();
        // Handle key
        if (primaryCode == Constant.CodeCancel) {
          hideCustomKeyboard();
        } else if (primaryCode == Constant.CodeDelete) {
          if (editable != null && start > 0) {
            editable.delete(start - 1, start);
          }
        } else {
          // Insert character
          editable.insert(start, Character.toString((char) primaryCode));
        }
      }
      @Override
      public void onPress(int arg0) {
      }
      @Override
      public void onRelease(int primaryCode) {
      }
      @Override
      public void onText(CharSequence text) {
      }
      @Override
      public void swipeDown() {
      }
      @Override
      public void swipeLeft() {
      }
      @Override
      public void swipeRight() {
      }
      @Override
      public void swipeUp() {
      }
    };
    mKeyboardView.setOnKeyboardActionListener(keyboardListener);
  }
  //绑定一个EditText
  public void registerEditText(EditText editText) {
    // Make the custom keyboard appear
    editText.setOnFocusChangeListener(new View.OnFocusChangeListener() {
      @Override
      public void onFocusChange(View v, boolean hasFocus) {
        if (hasFocus) {
          showCustomKeyboard(v);
        } else {
          hideCustomKeyboard();
        }
      }
    });
    editText.setOnClickListener(new View.OnClickListener() {
      @Override
      public void onClick(View v) {
        Log.d(TAG, "onClick");
        showCustomKeyboard(v);
      }
    });
    editText.setOnTouchListener(new View.OnTouchListener() {
      @Override
      public boolean onTouch(View v, MotionEvent event) {
        Log.d(TAG, "onTouch");
        EditText edittext = (EditText) v;
        int inType = edittext.getInputType();    // Backup the input type
        edittext.setInputType(InputType.TYPE_NULL); // Disable standard keyboard
        edittext.onTouchEvent(event);        // Call native handler
        edittext.setInputType(inType);       // Restore input type
        edittext.setSelection(edittext.getText().length());
        return true;
      }
    });
  }
  public void hideCustomKeyboard() {
    mKeyboardView.setVisibility(View.GONE);
    mKeyboardView.setEnabled(false);
  }
  public void showCustomKeyboard(View v) {
    mKeyboardView.setVisibility(View.VISIBLE);
    mKeyboardView.setEnabled(true);
    if (v != null) {
      ((InputMethodManager) mActivity.getSystemService(Activity.INPUT_METHOD_SERVICE)).hideSoftInputFromWindow(v.getWindowToken(), 0);
    }
  }
  public boolean isCustomKeyboardVisible() {
    return mKeyboardView.getVisibility() == View.VISIBLE;
  }
}

/**
 * 自定义安全输入法
 */
public class MainActivity extends ActionBarActivity {
  private KeyboardBuilder builder;
  @Override
  protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    getWindow().setSoftInputMode(WindowManager.LayoutParams.SOFT_INPUT_STATE_ALWAYS_HIDDEN);
    KeyboardView keyboardView = (KeyboardView) findViewById(R.id.keyboardview);
    builder = new KeyboardBuilder(this, keyboardView, R.xml.keys_layout);
    EditText editText = (EditText) findViewById(R.id.input_password);
    builder.registerEditText(editText);
    EditText editText2 = (EditText) findViewById(R.id.input_password2);
    builder.registerEditText(editText2);
  }
  @Override
  public void onBackPressed() {
    if (builder != null && builder.isCustomKeyboardVisible()) {
      builder.hideCustomKeyboard();
    } else {
      this.finish();
    }
  }
}