Draw in Canvas by finger, Android

Start By going through the Fingerpaint demo in the sdk sample.

Another Sample:

public class MainActivity extends Activity {

    DrawingView dv ;
    private Paint mPaint;    

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        dv = new DrawingView(this);
        setContentView(dv);
        mPaint = new Paint();
        mPaint.setAntiAlias(true);
        mPaint.setDither(true);
        mPaint.setColor(Color.GREEN);
        mPaint.setStyle(Paint.Style.STROKE);
        mPaint.setStrokeJoin(Paint.Join.ROUND);
        mPaint.setStrokeCap(Paint.Cap.ROUND);
        mPaint.setStrokeWidth(12);
    }

    public class DrawingView extends View {

        public int width;
        public  int height;
        private Bitmap  mBitmap;
        private Canvas  mCanvas;
        private Path    mPath;
        private Paint   mBitmapPaint;
        Context context;
        private Paint circlePaint;
        private Path circlePath;

        public DrawingView(Context c) {
            super(c);
            context=c;
            mPath = new Path();
            mBitmapPaint = new Paint(Paint.DITHER_FLAG);
            circlePaint = new Paint();
            circlePath = new Path();
            circlePaint.setAntiAlias(true);
            circlePaint.setColor(Color.BLUE);
            circlePaint.setStyle(Paint.Style.STROKE);
            circlePaint.setStrokeJoin(Paint.Join.MITER);
            circlePaint.setStrokeWidth(4f);
        }

        @Override
        protected void onSizeChanged(int w, int h, int oldw, int oldh) {
            super.onSizeChanged(w, h, oldw, oldh);

            mBitmap = Bitmap.createBitmap(w, h, Bitmap.Config.ARGB_8888);
            mCanvas = new Canvas(mBitmap);
        }

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

            canvas.drawBitmap( mBitmap, 0, 0, mBitmapPaint);
            canvas.drawPath( mPath,  mPaint);
            canvas.drawPath( circlePath,  circlePaint);
        }

        private float mX, mY;
        private static final float TOUCH_TOLERANCE = 4;

        private void touch_start(float x, float y) {
            mPath.reset();
            mPath.moveTo(x, y);
            mX = x;
            mY = y;
        }

        private void touch_move(float x, float y) {
            float dx = Math.abs(x - mX);
            float dy = Math.abs(y - mY);
            if (dx >= TOUCH_TOLERANCE || dy >= TOUCH_TOLERANCE) {
                mPath.quadTo(mX, mY, (x + mX)/2, (y + mY)/2);
                mX = x;
                mY = y;

                circlePath.reset();
                circlePath.addCircle(mX, mY, 30, Path.Direction.CW);
            }
        }

        private void touch_up() {
            mPath.lineTo(mX, mY);
            circlePath.reset();
            // commit the path to our offscreen
            mCanvas.drawPath(mPath,  mPaint);
            // kill this so we don't double draw
            mPath.reset();
        }

        @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();
                    invalidate();
                    break;
            }
            return true;
        }
    }
}

Snap shot

https://i.stack.imgur.com/BuAhe.png

Explanation :

You are creating a view class then extends View. You override the onDraw(). You add the path of where finger touches and moves. You override the onTouch() of this purpose. In your onDraw() you draw the paths using the paint of your choice. You should call invalidate() to refresh the view.

To choose options you can click menu and choose the options.

The below can be used as a reference. You can modify the below according to your needs.

public class FingerPaintActivity extends Activity
        implements ColorPickerDialog.OnColorChangedListener {

    MyView mv;
    AlertDialog dialog;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        mv= new MyView(this);
        mv.setDrawingCacheEnabled(true);
        mv.setBackgroundResource(R.drawable.afor);//set the back ground if you wish to
        setContentView(mv);
        mPaint = new Paint();
        mPaint.setAntiAlias(true);
        mPaint.setDither(true);
        mPaint.setColor(0xFFFF0000);
        mPaint.setStyle(Paint.Style.STROKE);
        mPaint.setStrokeJoin(Paint.Join.ROUND);
        mPaint.setStrokeCap(Paint.Cap.ROUND);
        mPaint.setStrokeWidth(20);
        mEmboss = new EmbossMaskFilter(new float[] { 1, 1, 1 },
                0.4f, 6, 3.5f);
        mBlur = new BlurMaskFilter(8, BlurMaskFilter.Blur.NORMAL);
    }

    private Paint       mPaint;
    private MaskFilter  mEmboss;
    private MaskFilter  mBlur;

    public void colorChanged(int color) {
        mPaint.setColor(color);
    }

    public class MyView extends View {

        private static final float MINP = 0.25f;
        private static final float MAXP = 0.75f;
        private Bitmap  mBitmap;
        private Canvas  mCanvas;
        private Path    mPath;
        private Paint   mBitmapPaint;
        Context context;

        public MyView(Context c) {
            super(c);
            context=c;
            mPath = new Path();
            mBitmapPaint = new Paint(Paint.DITHER_FLAG);

        }

        @Override
        protected void onSizeChanged(int w, int h, int oldw, int oldh) {
            super.onSizeChanged(w, h, oldw, oldh);
            mBitmap = Bitmap.createBitmap(w, h, Bitmap.Config.ARGB_8888);
            mCanvas = new Canvas(mBitmap);

        }

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

            canvas.drawBitmap(mBitmap, 0, 0, mBitmapPaint);
            canvas.drawPath(mPath, mPaint);
        }

        private float mX, mY;
        private static final float TOUCH_TOLERANCE = 4;

        private void touch_start(float x, float y) {
            //showDialog(); 
            mPath.reset();
            mPath.moveTo(x, y);
            mX = x;
            mY = y;

        }
        private void touch_move(float x, float y) {
            float dx = Math.abs(x - mX);
            float dy = Math.abs(y - mY);
            if (dx >= TOUCH_TOLERANCE || dy >= TOUCH_TOLERANCE) {
                mPath.quadTo(mX, mY, (x + mX)/2, (y + mY)/2);
                mX = x;
                mY = y;
            }
        }

        private void touch_up() {
            mPath.lineTo(mX, mY);
            // commit the path to our offscreen
            mCanvas.drawPath(mPath, mPaint);
            // kill this so we don't double draw
            mPath.reset();
            mPaint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.SCREEN));
            //mPaint.setMaskFilter(null);
        }

        @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();
                    invalidate();
                    break;
            }
            return true;
        }
    }

    private static final int COLOR_MENU_ID = Menu.FIRST;
    private static final int EMBOSS_MENU_ID = Menu.FIRST + 1;
    private static final int BLUR_MENU_ID = Menu.FIRST + 2;
    private static final int ERASE_MENU_ID = Menu.FIRST + 3;
    private static final int SRCATOP_MENU_ID = Menu.FIRST + 4;
    private static final int Save = Menu.FIRST + 5;

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        super.onCreateOptionsMenu(menu);

        menu.add(0, COLOR_MENU_ID, 0, "Color").setShortcut('3', 'c');
        menu.add(0, EMBOSS_MENU_ID, 0, "Emboss").setShortcut('4', 's');
        menu.add(0, BLUR_MENU_ID, 0, "Blur").setShortcut('5', 'z');
        menu.add(0, ERASE_MENU_ID, 0, "Erase").setShortcut('5', 'z');
        menu.add(0, SRCATOP_MENU_ID, 0, "SrcATop").setShortcut('5', 'z');
        menu.add(0, Save, 0, "Save").setShortcut('5', 'z');

        return true;
    }

    @Override
    public boolean onPrepareOptionsMenu(Menu menu) {
        super.onPrepareOptionsMenu(menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        mPaint.setXfermode(null);
        mPaint.setAlpha(0xFF);

        switch (item.getItemId()) {
            case COLOR_MENU_ID:
                new ColorPickerDialog(this, this, mPaint.getColor()).show();
                return true;
            case EMBOSS_MENU_ID:
                if (mPaint.getMaskFilter() != mEmboss) {
                    mPaint.setMaskFilter(mEmboss);
                } else {
                    mPaint.setMaskFilter(null);
                }
                return true;
            case BLUR_MENU_ID:
                if (mPaint.getMaskFilter() != mBlur) {
                    mPaint.setMaskFilter(mBlur);
                } else {
                    mPaint.setMaskFilter(null);
                }
                return true;
            case ERASE_MENU_ID:
                mPaint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.CLEAR));
                mPaint.setAlpha(0x80);
                return true;
            case SRCATOP_MENU_ID:

                mPaint.setXfermode(new PorterDuffXfermode(
                        PorterDuff.Mode.SRC_ATOP));
                mPaint.setAlpha(0x80);
                return true;
            case Save:
                AlertDialog.Builder editalert = new AlertDialog.Builder(FingerPaintActivity.this);
                editalert.setTitle("Please Enter the name with which you want to Save");
                final EditText input = new EditText(FingerPaintActivity.this);
                LinearLayout.LayoutParams lp = new LinearLayout.LayoutParams(
                        LinearLayout.LayoutParams.FILL_PARENT,
                        LinearLayout.LayoutParams.FILL_PARENT);
                input.setLayoutParams(lp);
                editalert.setView(input);
                editalert.setPositiveButton("OK", new DialogInterface.OnClickListener() {
                    public void onClick(DialogInterface dialog, int whichButton) {

                        String name= input.getText().toString();
                        Bitmap bitmap = mv.getDrawingCache();

                        String path = Environment.getExternalStorageDirectory().getAbsolutePath();
                        File file = new File("/sdcard/"+name+".png");
                        try
                        {
                            if(!file.exists())
                            {
                                file.createNewFile();
                            }
                            FileOutputStream ostream = new FileOutputStream(file);
                            bitmap.compress(CompressFormat.PNG, 10, ostream);
                            ostream.close();
                            mv.invalidate();
                        }
                        catch (Exception e)
                        {
                            e.printStackTrace();
                        }finally
                        {

                            mv.setDrawingCacheEnabled(false);
                        }
                    }
                });

                editalert.show();
                return true;
        }
        return super.onOptionsItemSelected(item);
    }
}

Color Picker

public class ColorPickerDialog extends Dialog {

    public interface OnColorChangedListener {
        void colorChanged(int color);
    }

    private OnColorChangedListener mListener;
    private int mInitialColor;

    private static class ColorPickerView extends View {
        private Paint mPaint;
        private Paint mCenterPaint;
        private final int[] mColors;
        private OnColorChangedListener mListener;

        ColorPickerView(Context c, OnColorChangedListener l, int color) {
            super(c);
            mListener = l;
            mColors = new int[] {
                    0xFFFF0000, 0xFFFF00FF, 0xFF0000FF, 0xFF00FFFF, 0xFF00FF00,
                    0xFFFFFF00, 0xFFFF0000
            };
            Shader s = new SweepGradient(0, 0, mColors, null);

            mPaint = new Paint(Paint.ANTI_ALIAS_FLAG);
            mPaint.setShader(s);
            mPaint.setStyle(Paint.Style.STROKE);
            mPaint.setStrokeWidth(32);

            mCenterPaint = new Paint(Paint.ANTI_ALIAS_FLAG);
            mCenterPaint.setColor(color);
            mCenterPaint.setStrokeWidth(5);
        }

        private boolean mTrackingCenter;
        private boolean mHighlightCenter;

        @Override
        protected void onDraw(Canvas canvas) {
            float r = CENTER_X - mPaint.getStrokeWidth()*0.5f;

            canvas.translate(CENTER_X, CENTER_X);

            canvas.drawOval(new RectF(-r, -r, r, r), mPaint);
            canvas.drawCircle(0, 0, CENTER_RADIUS, mCenterPaint);

            if (mTrackingCenter) {
                int c = mCenterPaint.getColor();
                mCenterPaint.setStyle(Paint.Style.STROKE);

                if (mHighlightCenter) {
                    mCenterPaint.setAlpha(0xFF);
                } else {
                    mCenterPaint.setAlpha(0x80);
                }
                canvas.drawCircle(0, 0,
                        CENTER_RADIUS + mCenterPaint.getStrokeWidth(),
                        mCenterPaint);

                mCenterPaint.setStyle(Paint.Style.FILL);
                mCenterPaint.setColor(c);
            }
        }

        @Override
        protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
            setMeasuredDimension(CENTER_X*2, CENTER_Y*2);
        }

        private static final int CENTER_X = 100;
        private static final int CENTER_Y = 100;
        private static final int CENTER_RADIUS = 32;

        private int floatToByte(float x) {
            int n = java.lang.Math.round(x);
            return n;
        }

        private int pinToByte(int n) {
            if (n < 0) {
                n = 0;
            } else if (n > 255) {
                n = 255;
            }
            return n;
        }

        private int ave(int s, int d, float p) {
            return s + java.lang.Math.round(p * (d - s));
        }

        private int interpColor(int colors[], float unit) {
            if (unit <= 0) {
                return colors[0];
            }
            if (unit >= 1) {
                return colors[colors.length - 1];
            }

            float p = unit * (colors.length - 1);
            int i = (int)p;
            p -= i;

            // now p is just the fractional part [0...1) and i is the index
            int c0 = colors[i];
            int c1 = colors[i+1];
            int a = ave(Color.alpha(c0), Color.alpha(c1), p);
            int r = ave(Color.red(c0), Color.red(c1), p);
            int g = ave(Color.green(c0), Color.green(c1), p);
            int b = ave(Color.blue(c0), Color.blue(c1), p);

            return Color.argb(a, r, g, b);
        }

        private int rotateColor(int color, float rad) {
            float deg = rad * 180 / 3.1415927f;
            int r = Color.red(color);
            int g = Color.green(color);
            int b = Color.blue(color);

            ColorMatrix cm = new ColorMatrix();
            ColorMatrix tmp = new ColorMatrix();

            cm.setRGB2YUV();
            tmp.setRotate(0, deg);
            cm.postConcat(tmp);
            tmp.setYUV2RGB();
            cm.postConcat(tmp);

            final float[] a = cm.getArray();

            int ir = floatToByte(a[0] * r +  a[1] * g +  a[2] * b);
            int ig = floatToByte(a[5] * r +  a[6] * g +  a[7] * b);
            int ib = floatToByte(a[10] * r + a[11] * g + a[12] * b);

            return Color.argb(Color.alpha(color), pinToByte(ir),
                    pinToByte(ig), pinToByte(ib));
        }

        private static final float PI = 3.1415926f;

        @Override
        public boolean onTouchEvent(MotionEvent event) {
            float x = event.getX() - CENTER_X;
            float y = event.getY() - CENTER_Y;
            boolean inCenter = java.lang.Math.sqrt(x*x + y*y) <= CENTER_RADIUS;

            switch (event.getAction()) {
                case MotionEvent.ACTION_DOWN:
                    mTrackingCenter = inCenter;
                    if (inCenter) {
                        mHighlightCenter = true;
                        invalidate();
                        break;
                    }
                case MotionEvent.ACTION_MOVE:
                    if (mTrackingCenter) {
                        if (mHighlightCenter != inCenter) {
                            mHighlightCenter = inCenter;
                            invalidate();
                        }
                    } else {
                        float angle = (float)java.lang.Math.atan2(y, x);
                        // need to turn angle [-PI ... PI] into unit [0....1]
                        float unit = angle/(2*PI);
                        if (unit < 0) {
                            unit += 1;
                        }
                        mCenterPaint.setColor(interpColor(mColors, unit));
                        invalidate();
                    }
                    break;
                case MotionEvent.ACTION_UP:
                    if (mTrackingCenter) {
                        if (inCenter) {
                            mListener.colorChanged(mCenterPaint.getColor());
                        }
                        mTrackingCenter = false;    // so we draw w/o halo
                        invalidate();
                    }
                    break;
            }
            return true;
        }
    }

    public ColorPickerDialog(Context context,
                             OnColorChangedListener listener,
                             int initialColor) {
        super(context);

        mListener = listener;
        mInitialColor = initialColor;
    }

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        OnColorChangedListener l = new OnColorChangedListener() {
            public void colorChanged(int color) {
                mListener.colorChanged(color);
                dismiss();
            }
        };

        setContentView(new ColorPickerView(getContext(), l, mInitialColor));
        setTitle("Pick a Color");
    }
}

Regarding the beautiful code of Raghunandan above.

Many have asked how to "clear" the drawing. Here's how to do that:

public void clearDrawing()
    {
    Utils.Log("RaghunandanDraw, how to clear....");

    setDrawingCacheEnabled(false);
    // don't forget that one and the match below,
    // or you just keep getting a duplicate when you save.

    onSizeChanged(width, height, width, height);
    invalidate();

    setDrawingCacheEnabled(true);
    }

@Override
protected void onSizeChanged(int w, int h, int oldw, int oldh)
    {
    super.onSizeChanged(w, h, oldw, oldh);

    width = w;      // don't forget these
    height = h;

    mBitmap = Bitmap.createBitmap(width, height, Bitmap.Config.ARGB_8888);
    mCanvas = new Canvas(mBitmap);
    }

Many have asked how to "save" the drawing. Here's how to do that:

public DrawingView(Context c)
  {
  circlePaint.setStrokeJoin(Paint.Join.MITER);
  circlePaint.setStrokeWidth(4f); 
  etc...

  // in the class where you set up the view, add this:
  setDrawingCacheEnabled( true );
  }

public void saveDrawing()
  {
  Bitmap whatTheUserDrewBitmap = getDrawingCache();
  // don't forget to clear it (see above) or you just get duplicates

  // almost always you will want to reduce res from the very high screen res
  whatTheUserDrewBitmap =
         ThumbnailUtils.extractThumbnail(whatTheUserDrewBitmap, 256, 256);
  // NOTE that's an incredibly useful trick for cropping/resizing squares
  // while handling all memory problems etc
  // http://stackoverflow.com/a/17733530/294884

  // you can now save the bitmap to a file, or display it in an ImageView:
  ImageView testArea = ...
  testArea.setImageBitmap( whatTheUserDrewBitmap );

  // these days you often need a "byte array". for example,
  // to save to parse.com or other cloud services
  ByteArrayOutputStream baos = new ByteArrayOutputStream();
  whatTheUserDrewBitmap.compress(Bitmap.CompressFormat.PNG, 0, baos);
  byte[] yourByteArray;
  yourByteArray = baos.toByteArray();
  }

Hope it helps someone as this has helped me.

You can use this class simply:

public class DoodleCanvas  extends View{

    private Paint mPaint;
    private Path mPath;

    public DoodleCanvas(Context context, AttributeSet attrs) {
        super(context, attrs);
        mPaint = new Paint();
        mPaint.setColor(Color.RED);
        mPaint.setStyle(Paint.Style.STROKE);
        mPaint.setStrokeJoin(Paint.Join.ROUND);
        mPaint.setStrokeCap(Paint.Cap.ROUND);
        mPaint.setStrokeWidth(10);
        mPath = new Path();
    }


    @Override
    protected void onDraw(Canvas canvas) {
        canvas.drawPath(mPath, mPaint);
        super.onDraw(canvas);
    }


    @Override
    public boolean onTouchEvent(MotionEvent event) {

        switch (event.getAction()){

            case MotionEvent.ACTION_DOWN:
                mPath.moveTo(event.getX(), event.getY());
                break;

            case MotionEvent.ACTION_MOVE:
                mPath.lineTo(event.getX(), event.getY());
                invalidate();
                break;

            case MotionEvent.ACTION_UP:
                break;
        }

        return true;
    }
}

tutorial to draw line use Bitmap, Canvas, and Paint class. draw-line-on-finger-touch and androiddraw

here one simple class to draw line using canvas as show below.

    public class TestLineView extends View {

    private Paint paint;
    private PointF startPoint, endPoint;
    private boolean isDrawing;

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

    private void init()
    {
        paint = new Paint();
        paint.setColor(Color.RED);
        paint.setStyle(Style.STROKE);
        paint.setStrokeWidth(2);
        paint.setAntiAlias(true);
    }

    @Override
    protected void onDraw(Canvas canvas)
    {
        if(isDrawing)
        {
            canvas.drawLine(startPoint.x, startPoint.y, endPoint.x, endPoint.y, paint);
        }
    }


    @Override
    public boolean onTouchEvent(MotionEvent event)
    {
        switch (event.getAction())
        {
            case MotionEvent.ACTION_DOWN:
                startPoint = new PointF(event.getX(), event.getY());
                endPoint = new PointF();
                isDrawing = true;
                break;
            case MotionEvent.ACTION_MOVE:
                if(isDrawing)
                {
                    endPoint.x = event.getX();
                    endPoint.y = event.getY();
                    invalidate();
                }
                break;
            case MotionEvent.ACTION_UP:
                if(isDrawing)
                {
                    endPoint.x = event.getX();
                    endPoint.y = event.getY();
                    isDrawing = false;
                    invalidate();
                }
                break;
            default:
                break;
        }
        return true;
    }
}

I think it's important to add a thing, if you use the layout inflation that constructor in the drawview is not correct, add these constructors in the class:

public DrawingView(Context c, AttributeSet attrs) {
    super(c, attrs);
    ...
}

public DrawingView(Context c, AttributeSet attrs, int defStyle) {
    super(c, attrs, defStyle);
    ...
}

or the android system fails to inflate the layout file. I hope this could to help.

In addition to Ishan's answer, if you want to draw programatically without user interaction, you can edit the class just a little like this.

public class DrawingCanvas extends View {

private Paint mPaint;
private Path mPath;
private boolean isUserInteractionEnabled = false;

public DrawingCanvas(Context context, AttributeSet attrs) {
    super(context, attrs);
    mPaint = new Paint();
    mPaint.setColor(Color.RED);
    mPaint.setStyle(Paint.Style.STROKE);
    mPaint.setStrokeJoin(Paint.Join.ROUND);
    mPaint.setStrokeCap(Paint.Cap.ROUND);
    mPaint.setStrokeWidth(10);
    mPath = new Path();
}


@Override
protected void onDraw(Canvas canvas) {
    canvas.drawPath(mPath, mPaint);
    super.onDraw(canvas);
}


@Override
public boolean onTouchEvent(MotionEvent event) {
    if (isUserInteractionEnabled) {
        switch (event.getAction()) {
            case MotionEvent.ACTION_DOWN:
                mPath.moveTo(event.getX(), event.getY());
                break;
            case MotionEvent.ACTION_MOVE:
                mPath.lineTo(event.getX(), event.getY());
                invalidate();
                break;
            case MotionEvent.ACTION_UP:
                break;
        }
    }

    return true;
}

public void moveCursorTo(float x, float y) {
    mPath.moveTo(x, y);
}

public void makeLine(float toX, float toY) {
    mPath.lineTo(toX, toY);
}

public void setUserInteractionEnabled(boolean userInteractionEnabled) {
    isUserInteractionEnabled = userInteractionEnabled;
}
}

And then use it like

drawingCanvas.setUserInteractionEnabled(true) // to enable user interaction
drawingCanvas.setUserInteractionEnabled(true) // to disable user interaction

To Draw programatically

drawingCanvas.moveCursorTo(70f, 70f) // Move the cursor (Define starting point)
drawingCanvas.makeLine(200f, 200f) // End point (To where you need to draw)