/**
 * 输入数字密码的键盘布局控件。
 */
public class PasswordKeyboardView extends KeyboardView implements
    android.inputmethodservice.KeyboardView.OnKeyboardActionListener {

  // 用于区分左下角空白的按键
  private static final int KEYCODE_EMPTY = -10;

  private int   mDeleteBackgroundColor;
  private Rect   mDeleteDrawRect;
  private Drawable mDeleteDrawable;

  private IOnKeyboardListener mOnKeyboardListener;

  public PasswordKeyboardView(Context context, AttributeSet attrs) {
    super(context, attrs);
    init(context, attrs, 0);
  }

  public PasswordKeyboardView(Context context, AttributeSet attrs,
      int defStyleAttr) {
    super(context, attrs, defStyleAttr);
    init(context, attrs, defStyleAttr);
  }

  private void init(Context context, AttributeSet attrs,
      int defStyleAttr) {
    TypedArray a = context.obtainStyledAttributes(attrs,
        R.styleable.PasswordKeyboardView, defStyleAttr, 0);
    mDeleteDrawable = a.getDrawable(
        R.styleable.PasswordKeyboardView_pkvDeleteDrawable);
    mDeleteBackgroundColor = a.getColor(
        R.styleable.PasswordKeyboardView_pkvDeleteBackgroundColor,
        Color.TRANSPARENT);
    a.recycle();

    // 设置软键盘按键的布局
    Keyboard keyboard = new Keyboard(context,
        R.xml.keyboard_number_password);
    setKeyboard(keyboard);

    setEnabled(true);
    setPreviewEnabled(false);
    setOnKeyboardActionListener(this);
  }

  @Override
  public void onDraw(Canvas canvas) {
    super.onDraw(canvas);

    // 遍历所有的按键
    List<Keyboard.Key> keys = getKeyboard().getKeys();
    for (Keyboard.Key key : keys) {
      // 如果是左下角空白的按键，重画按键的背景
      if (key.codes[0] == KEYCODE_EMPTY) {
        drawKeyBackground(key, canvas, mDeleteBackgroundColor);
      }
      // 如果是右下角的删除按键，重画背景，并且绘制删除的图标
      else if (key.codes[0] == Keyboard.KEYCODE_DELETE) {
        drawKeyBackground(key, canvas, mDeleteBackgroundColor);
        drawDeleteButton(key, canvas);
      }
    }
  }

  // 绘制按键的背景
  private void drawKeyBackground(Keyboard.Key key, Canvas canvas,
      int color) {
    ColorDrawable drawable = new ColorDrawable(color);
    drawable.setBounds(key.x, key.y,
        key.x + key.width, key.y + key.height);
    drawable.draw(canvas);
  }

  // 绘制删除按键
  private void drawDeleteButton(Keyboard.Key key, Canvas canvas) {
    if (mDeleteDrawable == null)
      return;

    // 计算删除图标绘制的坐标
    if (mDeleteDrawRect == null || mDeleteDrawRect.isEmpty()) {
      int intrinsicWidth = mDeleteDrawable.getIntrinsicWidth();
      int intrinsicHeight = mDeleteDrawable.getIntrinsicHeight();
      int drawWidth = intrinsicWidth;
      int drawHeight = intrinsicHeight;

      // 限制图标的大小，防止图标超出按键
      if (drawWidth > key.width) {
        drawWidth = key.width;
        drawHeight = drawWidth * intrinsicHeight / intrinsicWidth;
      }
      if (drawHeight > key.height) {
        drawHeight = key.height;
        drawWidth = drawHeight * intrinsicWidth / intrinsicHeight;
      }

      // 获取删除图标绘制的坐标
      int left = key.x + (key.width - drawWidth) / 2;
      int top = key.y + (key.height - drawHeight) / 2;
      mDeleteDrawRect = new Rect(left, top,
          left + drawWidth, top + drawHeight);
    }

    // 绘制删除的图标
    if (mDeleteDrawRect != null && !mDeleteDrawRect.isEmpty()) {
      mDeleteDrawable.setBounds(mDeleteDrawRect.left,
          mDeleteDrawRect.top, mDeleteDrawRect.right,
          mDeleteDrawRect.bottom);
      mDeleteDrawable.draw(canvas);
    }
  }

  @Override
  public void onKey(int primaryCode, int[] keyCodes) {
    // 处理按键的点击事件
    // 点击删除按键
    if (primaryCode == Keyboard.KEYCODE_DELETE) { 
      if (mOnKeyboardListener != null) {
        mOnKeyboardListener.onDeleteKeyEvent();
      }
    }
    // 点击了非左下角按键的其他按键
    else if (primaryCode != KEYCODE_EMPTY) {
      if (mOnKeyboardListener != null) {
        mOnKeyboardListener.onInsertKeyEvent(
            Character.toString((char) primaryCode));
      }
    }
  }

  @Override
  public void onPress(int primaryCode) {

  }

  @Override
  public void onRelease(int primaryCode) {

  }

  @Override
  public void onText(CharSequence text) {

  }

  @Override
  public void swipeLeft() {

  }

  @Override
  public void swipeRight() {

  }

  @Override
  public void swipeDown() {

  }

  @Override
  public void swipeUp() {

  }

  /**
   * 设置键盘的监听事件。
   *
   * @param listener
   *     监听事件
   */
  public void setIOnKeyboardListener(IOnKeyboardListener listener) {
    this.mOnKeyboardListener = listener;
  }

  public interface IOnKeyboardListener {

    void onInsertKeyEvent(String text);

    void onDeleteKeyEvent();
  }
}

<declare-styleable name="PasswordKeyboardView">
  <attr name="pkvDeleteDrawable" format="reference"/>
  <attr name="pkvDeleteBackgroundColor" format="color|reference"/>
</declare-styleable>

<?xml version="1.0" encoding="utf-8"?>
<Keyboard
  xmlns:android="http://schemas.android.com/apk/res/android"
  android:keyWidth="33.33333%p"
  android:keyHeight="8%p"
  android:horizontalGap="1dp"
  android:verticalGap="1dp">
  <Row>
    <Key
      android:codes="49"
      android:keyLabel="1"/>
    <Key
      android:codes="50"
      android:keyLabel="2"/>
    <Key
      android:codes="51"
      android:keyLabel="3"/>
  </Row>

  <Row>
    <Key
      android:codes="52"
      android:keyLabel="4"/>
    <Key
      android:codes="53"
      android:keyLabel="5"/>
    <Key
      android:codes="54"
      android:keyLabel="6"/>
  </Row>

  <Row>
    <Key
      android:codes="55"
      android:keyLabel="7"/>
    <Key
      android:codes="56"
      android:keyLabel="8"/>
    <Key
      android:codes="57"
      android:keyLabel="9"/>
  </Row>

  <Row>
    <Key
      android:codes="-10"
      android:keyLabel=""/>
    <Key
      android:codes="48"
      android:keyLabel="0"/>
    <Key
      android:codes="-5"
      android:keyIcon="@mipmap/keyboard_backspace"/>
  </Row>
</Keyboard>

<[包名].PasswordKeyboardView
  android:layout_width="match_parent"
  android:layout_height="wrap_content"
  android:background="#b0b0b0"
  android:focusable="true"
  android:focusableInTouchMode="true"
  android:keyBackground="#ffffff"
  android:keyTextColor="#000000"
  android:shadowColor="#00000000"
  android:shadowRadius="0"
  app:pkvDeleteBackgroundColor="#d2d2d2"
  app:pkvDeleteDrawable="@drawable/keyboard_backspace" />

// 0-9 的数字
private final List<Character> keyCodes = Arrays.asList(
    '0', '1', '2', '3', '4', '5', '6', '7', '8', '9');

/**
 * 随机打乱数字键盘上显示的数字顺序。
 */
public void shuffleKeyboard() {
  Keyboard keyboard = getKeyboard();
  if (keyboard != null && keyboard.getKeys() != null
      && keyboard.getKeys().size() > 0) {
    // 随机排序数字
    Collections.shuffle(keyCodes);

    // 遍历所有的按键
    List<Keyboard.Key> keys = getKeyboard().getKeys();
    int index = 0;
    for (Keyboard.Key key : keys) {
      // 如果按键是数字
      if (key.codes[0] != KEYCODE_EMPTY
          && key.codes[0] != Keyboard.KEYCODE_DELETE) {
        char code = keyCodes.get(index++);
        key.codes[0] = code;
        key.label = Character.toString(code);
      }
    }
    // 更新键盘
    setKeyboard(keyboard);
  }
}

<[包名].PasswordKeyboardView
  android:shadowColor="@color/transparent"
  android:shadowRadius="0"
  ...
  />