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Editorial Team
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Asked: 2026-06-16T01:12:04+00:00

I can actually draw lines with finger in my app using the FingerPaint in

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I can actually draw lines with finger in my app using the FingerPaint in API Demos given in samples of Android SDK. But how to draw these lines with finger only along points placed on the screen. I want something like in this app:https://play.google.com/store/apps/details?id=zok.android.dots
enter image description here
I just want to draw line between point 1 and point 2 with finger. The line between 1 and 2 must be drawn only if the point 2 is touched, else it shouldn’t be drawn. Likewise, again from point 2 to point 3 and so on.
Please help me with a code for this.
Thanks in advance

P.S. Please have a look at the app in the link well before answering so that you would have a clear idea about my requirement.

Update:

public class PaintView extends View {

private Bitmap mBitmap;
private Canvas mCanvas;
private Path mPath;
private Paint mPaint;
private static final int TOUCH_TOLERANCE_DP = 20;
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 PaintView(Context context) {
    super(context);
    mCanvas = new Canvas();
    mPath = new Path();
    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);

    // TODO just test points
    Point p1 = new Point(133, 123);
    Point p2 = new Point(149, 136);
    Point p3 = new Point(182, 136);
    Point p4 = new Point(206, 118);
    Point p5 = new Point(208, 87);
    Point p6 = new Point(187, 71);
    Point p7 = new Point(144, 78);
    Point p8 = new Point(124, 101);
    Point p9 = new Point(113, 128);
    Point p10 = new Point(112, 157);
    Point p11 = new Point(119, 188);
    Point p12 = new Point(134, 209);
    Point p13 = new Point(162, 228);
    Point p14 = new Point(194, 238);
    Point p15 = new Point(232, 240);
    Point p16 = new Point(263, 237);
    Point p17 = new Point(289, 224);
    Point p18 = new Point(315, 204);
    Point p19 = new Point(332, 174);
    Point p20 = new Point(339, 128);
    Point p21 = new Point(329, 95);
    Point p22 = new Point(304, 73);
    Point p23 = new Point(280, 69);
    Point p24 = new Point(254, 87);
    Point p25 = new Point(248, 116);
    Point p26 = new Point(259, 143);
    Point p27 = new Point(278, 153);
    Point p28 = new Point(241, 157);
    Point p29 = new Point(192, 160);
    Point p30 = new Point(150, 159);
    mPoints.add(p1);
    mPoints.add(p2);
    mPoints.add(p3);
    mPoints.add(p4);
    mPoints.add(p5);
    mPoints.add(p6);
    mPoints.add(p7);
    mPoints.add(p8);
    mPoints.add(p9);
    mPoints.add(p10);
    mPoints.add(p11);
    mPoints.add(p12);
    mPoints.add(p13);
    mPoints.add(p14);
    mPoints.add(p15);
    mPoints.add(p16);
    mPoints.add(p17);
    mPoints.add(p18);
    mPoints.add(p19);
    mPoints.add(p20);
    mPoints.add(p21);
    mPoints.add(p22);
    mPoints.add(p23);
    mPoints.add(p24);
    mPoints.add(p25);
    mPoints.add(p26);
    mPoints.add(p27);
    mPoints.add(p28);
    mPoints.add(p29);
    mPoints.add(p30);
}

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

    // TODO just test points
    Point p1 = new Point(133, 123);
    Point p2 = new Point(149, 136);
    Point p3 = new Point(182, 136);
    Point p4 = new Point(206, 118);
    Point p5 = new Point(208, 87);
    Point p6 = new Point(187, 71);
    Point p7 = new Point(144, 78);
    Point p8 = new Point(124, 101);
    Point p9 = new Point(113, 128);
    Point p10 = new Point(112, 157);
    Point p11 = new Point(119, 188);
    Point p12 = new Point(134, 209);
    Point p13 = new Point(162, 228);
    Point p14 = new Point(194, 238);
    Point p15 = new Point(232, 240);
    Point p16 = new Point(263, 237);
    Point p17 = new Point(289, 224);
    Point p18 = new Point(315, 204);
    Point p19 = new Point(332, 174);
    Point p20 = new Point(339, 128);
    Point p21 = new Point(329, 95);
    Point p22 = new Point(304, 73);
    Point p23 = new Point(280, 69);
    Point p24 = new Point(254, 87);
    Point p25 = new Point(248, 116);
    Point p26 = new Point(259, 143);
    Point p27 = new Point(278, 153);
    Point p28 = new Point(241, 157);
    Point p29 = new Point(192, 160);
    Point p30 = new Point(150, 159);
    mPoints.add(p1);
    mPoints.add(p2);
    mPoints.add(p3);
    mPoints.add(p4);
    mPoints.add(p5);
    mPoints.add(p6);
    mPoints.add(p7);
    mPoints.add(p8);
    mPoints.add(p9);
    mPoints.add(p10);
    mPoints.add(p11);
    mPoints.add(p12);
    mPoints.add(p13);
    mPoints.add(p14);
    mPoints.add(p15);
    mPoints.add(p16);
    mPoints.add(p17);
    mPoints.add(p18);
    mPoints.add(p19);
    mPoints.add(p20);
    mPoints.add(p21);
    mPoints.add(p22);
    mPoints.add(p23);
    mPoints.add(p24);
    mPoints.add(p25);
    mPoints.add(p26);
    mPoints.add(p27);
    mPoints.add(p28);
    mPoints.add(p29);
    mPoints.add(p30);
}

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

@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;
    }

}

//ADDED WITH LAST EDIT
private void touch_move(float x, float y) {
    // draw line with finger move
    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);
        }
    }
}

/**
 * Draws line.
 */
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;
    }

}

/**
 * Sets paint
 * 
 * @param paint
 */
public void setPaint(Paint paint) {
    this.mPaint = paint;
}

/**
 * Returns image as bitmap
 * 
 * @return
 */
public Bitmap getBitmap() {
    return mBitmap;
}

/**
 * Clears canvas
 */
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.y + 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 int dp2px(int dp) {
    Resources r = getContext().getResources();
    float px = TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_DIP, dp, r.getDisplayMetrics());
    return (int) px;
}
}

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1 Answer

  1. Editorial Team

    I done something similar but I’m not sure if it’s exactly what you’re expecting. Try this implementation of PaintView:

    Edit:
    Added touch_move() to drawn line along finger move.

    Edit2:
    To draw multiple lines with one move change touch_move() method to this one:

    private void touch_move(float x, float y) {
// draw line with finger move
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);
    }
}
}

    _

    public class PaintView 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 PaintView(Context context) {
    super(context);
    mCanvas = new Canvas();
    mPath = new Path();
    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);

    // TODO just test points
    Point p1 = new Point(20, 20);
    Point p2 = new Point(100, 100);
    Point p3 = new Point(200, 250);
    Point p4 = new Point(280, 400);
    Point p5 = new Point(350, 600);
    Point p6 = new Point(400, 500);
    mPoints.add(p1);
    mPoints.add(p2);
    mPoints.add(p3);
    mPoints.add(p4);
    mPoints.add(p5);
    mPoints.add(p6);
}

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

    // TODO just test points
    Point p1 = new Point(20, 20);
    Point p2 = new Point(100, 100);
    Point p3 = new Point(200, 250);
    Point p4 = new Point(280, 400);
    Point p5 = new Point(350, 600);
    Point p6 = new Point(400, 500);
    mPoints.add(p1);
    mPoints.add(p2);
    mPoints.add(p3);
    mPoints.add(p4);
    mPoints.add(p5);
    mPoints.add(p6);
}

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

@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;
    }

}

//ADDED WITH LAST EDIT
private void touch_move(float x, float y) {
    // draw line with finger move
    if (isPathStarted) {
        mPath.reset();
        Point p = mPoints.get(mLastPointIndex);
        mPath.moveTo(p.x, p.y);
        mPath.lineTo(x, y);
    }
}

/**
 * Draws line.
 */
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;
    }

}

/**
 * Sets paint
 * 
 * @param paint
 */
public void setPaint(Paint paint) {
    this.mPaint = paint;
}

/**
 * Returns image as bitmap
 * 
 * @return
 */
public Bitmap getBitmap() {
    return mBitmap;
}

/**
 * Clears canvas
 */
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);
    //EDIT changed point.y to poin.x in the first if statement
    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 int dp2px(int dp) {
    Resources r = getContext().getResources();
    float px = TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_DIP, dp, r.getDisplayMetrics());
    return (int) px;
}

    }

    I used it from xml but you can also create it from code, simple xml:

    <RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity" >

    <com.example.lecho.PaintView
        android:layout_width="match_parent"
        android:layout_height="match_parent"/>

</RelativeLayout>
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