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POHow to change paint color/stroke after implementing UNDO function in canvas paint
 

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  1. POHow to change paint color/stroke after implementing UNDO function in canvas paint
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    <p>In my Paint App I have implemented UNDO function and it's working fine. But if a change the paint brush color (or) paint brush stroke then all my previous drawn paths changing to the new paint color. The code is as follows:</p> <pre><code>public class CustomView extends View implements OnTouchListener { public Canvas mCanvas; private Path mPath; public Paint mPaint, mBitmapPaint; Bitmap mBitmap; Canvas canvas; public ArrayList&lt;Path&gt; paths = new ArrayList&lt;Path&gt;(); public ArrayList&lt;Path&gt; undonePaths = new ArrayList&lt;Path&gt;(); private Bitmap im; public CustomView(Context context) { super(context); setFocusable(true); setFocusableInTouchMode(true); setOnTouchListener(this); mPaint = new Paint(); mPaint.setAntiAlias(true); mPaint.setDither(true); mPaint.setColor(0xFFFFFFFF); mPaint.setStyle(Paint.Style.STROKE); mPaint.setStrokeJoin(Paint.Join.ROUND); mPaint.setStrokeCap(Paint.Cap.ROUND); mPaint.setStrokeWidth(6); mCanvas = new Canvas(); mPath = new Path(); im = BitmapFactory.decodeResource(context.getResources(), R.drawable.ic_launcher); DisplayMetrics metrics = getContext().getResources().getDisplayMetrics(); int w = metrics.widthPixels; int h = metrics.heightPixels; mBitmap = Bitmap.createBitmap(w, h, Bitmap.Config.ARGB_8888); mBitmapPaint = new Paint(Paint.DITHER_FLAG); // mBitmapPaint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.SRC)); } @Override protected void onSizeChanged(int w, int h, int oldw, int oldh) { super.onSizeChanged(w, h, oldw, oldh); } @Override protected void onDraw(Canvas canvas) { // mPath = new Path(); // canvas.drawPath(mPath, mPaint); canvas.drawColor(Color.TRANSPARENT); canvas.drawBitmap(mBitmap, 0, 0, mBitmapPaint); for (Path p : paths) { canvas.drawPath(p, mPaint); } canvas.drawPath(mPath, mPaint); } private float mX, mY; private static final float TOUCH_TOLERANCE = 4; private void touch_start(float x, float y) { undonePaths.clear(); 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 &gt;= TOUCH_TOLERANCE || dy &gt;= 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 paths.add(mPath); mPath = new Path(); } public void onClickUndo() { if (paths.size() &gt; 0) { undonePaths.add(paths.remove(paths.size() - 1)); invalidate(); } else { } // toast the user } public void onClickRedo() { if (undonePaths.size() &gt; 0) { paths.add(undonePaths.remove(undonePaths.size() - 1)); invalidate(); } else { } // toast the user } @Override public boolean onTouch(View arg0, 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; } } </code></pre>
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    1. COafter you undo, you should call invalidate() function with params that specificy the will-be-updated portion of screen, you now callign invalidate() without params which leads to whole screen update so the colors of previous touches also change.
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