Connect dots android view.

ConnectDotsView.java

public class ConnectDotsView extends View {

private Bitmap mBitmap;
private Canvas mCanvas;
private Path mPath;
private Paint mPaint;
private static final int TOUCH_TOLERANCE_DP = 24;
private static final int BACKGROUND = 0xFFDDDDDD;
private List<Point> mPoints = new ArrayList<Point>();
private int mLastPointIndex = 0;
private int mTouchTolerance;
private boolean isPathStarted = false;

public ConnectDotsView(Context context) {
    super(context);
    mCanvas = new Canvas();
    mPath = new Path();
  initPaint();
}

public ConnectDotsView(Context context, AttributeSet attrs) {
    super(context, attrs);
    mCanvas = new Canvas();
    mPath = new Path();
	initPaint();
}

public ConnectDotsView(Context context, AttributeSet attrs, int defStyle) {
    super(context, attrs, defStyle);
    mCanvas = new Canvas();
    mPath = new Path();
	initPaint();
}

@Override
protected void onSizeChanged(int width, int height, int oldWidth, int oldHeight) {
    super.onSizeChanged(width, height, oldWidth, oldHeight);
    clear();

}

@Override
protected void onDraw(Canvas canvas) {
    canvas.drawColor(BACKGROUND);
    canvas.drawBitmap(mBitmap, 0, 0, null);
    canvas.drawPath(mPath, mPaint);

    // TODO remove if you dont want points to be drawn
    for (Point point : mPoints) {
        canvas.drawPoint(point.x, point.y, mPaint);
    }
}

@Override
public boolean onTouchEvent(MotionEvent event) {
    float x = event.getX();
    float y = event.getY();

    switch (event.getAction()) {
        case MotionEvent.ACTION_DOWN:
            touch_start(x, y);
            invalidate();
            break;
        case MotionEvent.ACTION_MOVE:
            touch_move(x, y);
            invalidate();
            break;
        case MotionEvent.ACTION_UP:
            touch_up(x, y);
            invalidate();
            break;
    }
    return true;
}

private void touch_start(float x, float y) {

    if (checkPoint(x, y, mLastPointIndex)) {
        mPath.reset();
        // user starts from given point so path can beis started
        isPathStarted = true;
    } else {
        // user starts move from point which doen's belongs to mPinst list
        isPathStarted = false;
    }

}

private void touch_move(float x, float y) {
	if (isPathStarted) {
		mPath.reset();
		Point p = mPoints.get(mLastPointIndex);
		mPath.moveTo(p.x, p.y);
		if (checkPoint(x, y, mLastPointIndex + 1)) {
			p = mPoints.get(mLastPointIndex + 1);
			mPath.lineTo(p.x, p.y);
			mCanvas.drawPath(mPath, mPaint);
			mPath.reset();
			++mLastPointIndex;
		} else {
        mPath.lineTo(x, y);
		}
	}
}

private void touch_up(float x, float y) {
    mPath.reset();
    if (checkPoint(x, y, mLastPointIndex + 1) && isPathStarted) {
        // move finished at valid point so draw whole line

        // start point
        Point p = mPoints.get(mLastPointIndex);
        mPath.moveTo(p.x, p.y);
        // end point
        p = mPoints.get(mLastPointIndex + 1);
        mPath.lineTo(p.x, p.y);
        mCanvas.drawPath(mPath, mPaint);
        mPath.reset();
        // increment point index
        ++mLastPointIndex;
        isPathStarted = false;
    }

}

public void setPaint(Paint paint) {
    this.mPaint = paint;
}

public Bitmap getBitmap() {
    return mBitmap;
}

public void clear() {
    mBitmap = Bitmap.createBitmap(getWidth(), getHeight(), Bitmap.Config.ARGB_8888);
    mBitmap.eraseColor(BACKGROUND);
    mCanvas.setBitmap(mBitmap);
    invalidate();
}

/**
 * Checks if user touch point with some tolerance
 */
private boolean checkPoint(float x, float y, int pointIndex) {
    if (pointIndex == mPoints.size()) {
        // out of bounds
        return false;
    }
    Point point = mPoints.get(pointIndex);
    if (x > (point.x - mTouchTolerance) && x < (point.x + mTouchTolerance)) {
        if (y > (point.y - mTouchTolerance) && y < (point.y + mTouchTolerance)) {
            return true;
        }
    }
    return false;
}

public List<Point> getPoints() {
    return mPoints;
}

public void setPoints(List<Point> points) {
    this.mPoints = points;
}

private void initPaint(){
    mPaint = new Paint();
    mPaint.setAntiAlias(true);
    mPaint.setDither(true);
    mPaint.setColor(Color.BLACK);
    mPaint.setStyle(Paint.Style.STROKE);
    mPaint.setStrokeJoin(Paint.Join.ROUND);
    mPaint.setStrokeCap(Paint.Cap.ROUND);
    mPaint.setStrokeWidth(12);
    mTouchTolerance = dp2px(TOUCH_TOLERANCE_DP);
}

private int dp2px(int dp) {
    Resources r = getContext().getResources();
    float px = TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_DIP, dp, r.getDisplayMetrics());
    return (int) px;
}