Android - How to draw on view

Question

I am tring to paint on my own view (R.id.view) but this code does not seem to have any effect. It is not allowing me to draw anything at all.

public class MainActivity extends Activity implements OnTouchListener
        {
Path mPath;
Canvas canvas;
Paint mPaint;
MaskFilter mEmboss;

    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        View view=(View)findViewById(R.id.view1);
        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(12);

        canvas = null;
        //view.draw(canvas);
        mPath = new Path();
        Bitmap mBitmap;
        //Paint mBitmapPaint = new Paint(Paint.DITHER_FLAG);
        mBitmap = Bitmap.createBitmap(210, 170, Bitmap.Config.ARGB_8888);
        canvas = new Canvas(mBitmap);
        canvas.drawColor(0xFFAAAAAA);

        canvas.drawBitmap(mBitmap, 0, 0, mPaint);


        //canvas.drawPaint(mPaint);
        view.draw(canvas);
        canvas.drawPath(mPath, mPaint);


        mEmboss = new EmbossMaskFilter(new float[] { 1, 1, 1 },
                                       0.4f, 6, 3.5f);



        view.setOnTouchListener(new OnTouchListener() {

            public boolean onTouch(View v, MotionEvent event) {
                float x = event.getX();
                float y = event.getY();
                Log.d("x", String.valueOf(x));
                Log.d("y", String.valueOf(y));

                switch (event.getAction()) {
                    case MotionEvent.ACTION_DOWN:
                        Log.d("a","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;
            }
        });

       // mBlur = new BlurMaskFilter(8, BlurMaskFilter.Blur.NORMAL);
    }
    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;
        }
    }
    private void touch_up() {
        mPath.lineTo(mX, mY);
        // commit the path to our offscreen
        canvas.drawPath(mPath, mPaint);
        // kill this so we don't double draw
        mPath.reset();
    }





}

What do I do to use the freehanf finger paint on my own view?

score 9 · Accepted Answer · edited Oct 21 '21 at 22:00

It would be best if you made a class that extended view, and set that to the content view. It's more dynamic that way.

Also, the Action_Move parameter gets called a lot during touch events, so it might be best to take note of that, otherwise you'll get a straight line when you wanted a curve.

You would start off in the onCreate by changing

View view = new MyView();
setContentView(view);

Inside of your MyView class you would have an ArrayList of Path objects. Every time Action_UP gets called, you add the path to the ArrayList, use view.Invalidate(); and then the class will call the onDraw Method in your view class. So you override it like so:

@Override
public void onDraw(Canvas c) {
    for (Path p : listOfPaths) {
        c.drawPath(p, paint);
    }
}

Note that while this would be good for simple drawing, don't expect to draw the Mona Lisa on your tablet or phone with this method since once there are many lines you might notice lag. If you want to get more complicated and professional, check out the view.Invalidate(Rect r) approach, which won't invalidate the whole view but only the portion you just drew.

Any class that extends view will have a onDraw method. Simply call invalidate during your Action_Up, and it will call the onDraw Method. to redraw the updated view. Hope this helped. — dannyRods, Dec 13 '12 at 02:58
can we get more information? How would you do this within his code? — Music Monkey, Jan 15 '13 at 14:54

Android - How to draw on view

1 Answers1