public class MainActivity extends AppCompatActivity {

  @Override
  protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    NineView view = new NineView(this);
    setContentView(view);
    view.setOnPasswordFinishListener(new NineView.OnPasswordFinishListener() {
      @Override
      public void onPasswordFinish(String password) {
        Toast.makeText(getBaseContext(), "密碼:" + password, Toast.LENGTH_SHORT).show();
      }
    });
  }
}

public class NineView extends View {

  int width;
  Paint paintback = new Paint();
  Paint paintsrc = new Paint();
  int background;

  //保證是正方形

  int max = 6; //密碼的個數  6
  int min = 4;


  //點在哪里
  float currX, currY;

  public NineView(Context context) {
    super(context);
    init();
  }

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

  public void init() {
    paintback.setDither(true);
    paintback.setAntiAlias(true);
    paintsrc.setDither(true);
    paintsrc.setAntiAlias(true);
    //171625
    background = Color.rgb(0x17, 0x16, 0x25);
    paintback.setColor(background);
    //3791E6
    paintsrc.setColor(Color.rgb(0x37, 0x91, 0xe6));


  }

  @Override
  protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
    super.onMeasure(widthMeasureSpec, heightMeasureSpec);
    width = getWidth() / 4;

  }

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

    //清屏
    canvas.drawColor(background);
    //劃線
    if (result.size() > 0) {


      //點
      int x = result.get(result.size() - 1) % 3 + 1;
      int y = result.get(result.size() - 1) / 3 + 1;
      paintsrc.setStrokeWidth(10);
      canvas.drawLine(x * width, y * width, currX, currY, paintsrc);
      canvas.drawCircle(x * width, y * width, width / 3, paintback);
      if (result.size() > 1) {
        //防止越界
        for (int i = 0; i < result.size() - 1; i++) { // 1 2 3 <=2
          //需要取當前的i和下一個i
          //按住的前一個點
          int x1 = result.get(i) % 3 + 1;
          int y1 = result.get(i) / 3 + 1;
          //按住的后一個點
          int x2 = result.get(i + 1) % 3 + 1;
          int y2 = result.get(i + 1) / 3 + 1;
          paintsrc.setStrokeWidth(10);
          canvas.drawLine(x1 * width, y1 * width, x2 * width, y2 * width, paintsrc);
          canvas.drawCircle(x1 * width, y1 * width, width / 3, paintback);

        }
      }
    }
    paintsrc.setStrokeWidth(2);
    //9個圓
    paintsrc.setStyle(Paint.Style.STROKE);
    for (int i = 0; i < 3; i++) {
      for (int j = 0; j < 3; j++) {
        canvas.drawCircle((i + 1) * width, (j + 1) * width, width / 3, paintsrc);
      }
    }
    paintsrc.setStyle(Paint.Style.FILL);
    for (Integer integer : result) {
      //i j ; // 8  2 2
      int j = integer / 3 + 1;
      int i = integer % 3 + 1;
      canvas.drawCircle(i * width, j * width, width / 8, paintsrc);
    }

  }

  //密碼
  List<Integer> result = new ArrayList<>();

  @Override
  public boolean onTouchEvent(MotionEvent event) {
    float x = event.getX();
    float y = event.getY();
    switch (event.getAction()) {
      case MotionEvent.ACTION_DOWN:
        //勾股定理
        int i = isConnPoint(x, y);
        //只要在園內
        if (i != -1) {
          result.add(i);
          currX = x;
          currY = y;
        }
        Log.e("TAG", "=====" + i);
        break;
      case MotionEvent.ACTION_MOVE:
        currX = x;
        currY = y;
        //移動到其他的圓中，那么接著去添加result
        int point = isConnPoint(x, y);
        if (point != -1 && !result.contains((Integer) point)) {
          result.add(point);
          if (result.size() > max) {
            //reslut清空
            if (onPasswordFinishListener != null)
              onPasswordFinishListener.onPasswordFinish(getPassword());
            result.clear();
          }
        }
        break;
      case MotionEvent.ACTION_UP:
        if (result.size() >= min) {
          if (onPasswordFinishListener != null)
            onPasswordFinishListener.onPasswordFinish(getPassword());
        }
        result.clear();
        break;
    }
    invalidate();
    return true;
  }

  public String getPassword() {
    String password = "";
    for (Integer integer : result) {
      password += integer + "";
    }
    return password;
  }


  //判斷
  public int isConnPoint(float x, float y) {
    //9  width,width width
    for (int i = 0; i < 3; i++) {
      for (int j = 0; j < 3; j++) {
        if (pointOnCircle(x, y, (j + 1) * width, (i + 1) * width)) {
          return i * 3 + j; //0-8
        }
      }
    }
    return -1;
  }

  public boolean pointOnCircle(float x, float y, int cx, int cy) {//true
    Log.e("TAG", ((cx - x) * (cx - x) + (cy - y) * (cy - y)) + "");
    Log.e("TAG", ((float) width / 3f) * ((float) width / 3f) + "");
    float i = ((cx - x) * (cx - x) + (cy - y) * (cy - y));
    float j = ((float) width / 3f) * ((float) width / 3f);
    return i < j;
  }


  public void setOnPasswordFinishListener(OnPasswordFinishListener onPasswordFinishListener) {
    this.onPasswordFinishListener = onPasswordFinishListener;
  }

  private OnPasswordFinishListener onPasswordFinishListener;

  public interface OnPasswordFinishListener {
    void onPasswordFinish(String password);
  }

}