We Keep Coding

Signature view not working on Android 8 + devices

I am working on an application which captures an applicant's signature and saves it to the phone memory. The class used for the signature view is given below
public class SignatureView extends View {
private static final float STROKE_WIDTH = 5f;
/** Need to track this so the dirty region can accommodate the stroke. **/
private static final float HALF_STROKE_WIDTH = STROKE_WIDTH / 2;
private Paint paint = new Paint();
private Path path = new Path();
/**
* Optimizes painting by invalidating the smallest possible area.
*/
private float lastTouchX;
private float lastTouchY;
private final RectF dirtyRect = new RectF();
public SignatureView(Context context, AttributeSet attrs) {
super(context, attrs);
paint.setAntiAlias(true);
paint.setColor(Color.BLACK);
paint.setStyle(Paint.Style.STROKE);
paint.setStrokeJoin(Paint.Join.ROUND);
paint.setStrokeWidth(STROKE_WIDTH);
}
/**
* Erases the signature.
*/
public void clear() {
path.reset();
// Repaints the entire view.
invalidate();
}
#Override
protected void onDraw(Canvas canvas) {
canvas.drawARGB(255, 233, 255, 255);
canvas.drawPath(path, paint);
}
#Override
public boolean onTouchEvent(MotionEvent event) {
float eventX = event.getX();
float eventY = event.getY();
switch (event.getAction()) {
case MotionEvent.ACTION_DOWN:
path.moveTo(eventX, eventY);
lastTouchX = eventX;
lastTouchY = eventY;
// There is no end point yet, so don't waste cycles invalidating.
return true;
case MotionEvent.ACTION_MOVE:
case MotionEvent.ACTION_UP:
// Start tracking the dirty region.
resetDirtyRect(eventX, eventY);
// When the hardware tracks events faster than they are delivered, the
// event will contain a history of those skipped points.
int historySize = event.getHistorySize();
for (int i = 0; i < historySize; i++) {
float historicalX = event.getHistoricalX(i);
float historicalY = event.getHistoricalY(i);
expandDirtyRect(historicalX, historicalY);
path.lineTo(historicalX, historicalY);
}
// After replaying history, connect the line to the touch point.
path.lineTo(eventX, eventY);
break;
default:
//debug("Ignored touch event: " + event.toString());
return false;
}
// Include half the stroke width to avoid clipping.
invalidate(
(int) (dirtyRect.left - HALF_STROKE_WIDTH),
(int) (dirtyRect.top - HALF_STROKE_WIDTH),
(int) (dirtyRect.right + HALF_STROKE_WIDTH),
(int) (dirtyRect.bottom + HALF_STROKE_WIDTH));
lastTouchX = eventX;
lastTouchY = eventY;
return true;
}
/**
* Called when replaying history to ensure the dirty region includes all
* points.
*/
private void expandDirtyRect(float historicalX, float historicalY) {
if (historicalX < dirtyRect.left) {
dirtyRect.left = historicalX;
} else if (historicalX > dirtyRect.right) {
dirtyRect.right = historicalX;
}
if (historicalY < dirtyRect.top) {
dirtyRect.top = historicalY;
} else if (historicalY > dirtyRect.bottom) {
dirtyRect.bottom = historicalY;
}
}
/**
* Resets the dirty region when the motion event occurs.
*/
private void resetDirtyRect(float eventX, float eventY) {
// The lastTouchX and lastTouchY were set when the ACTION_DOWN
// motion event occurred.
dirtyRect.left = Math.min(lastTouchX, eventX);
dirtyRect.right = Math.max(lastTouchX, eventX);
dirtyRect.top = Math.min(lastTouchY, eventY);
dirtyRect.bottom = Math.max(lastTouchY, eventY);
}
// get drawn image as bitmap
public Bitmap getBitmap() {
this.setDrawingCacheEnabled(true);
this.buildDrawingCache();
Bitmap bmp = Bitmap.createBitmap(this.getDrawingCache());
this.setDrawingCacheEnabled(false);
return bmp;
}
public boolean isDrawn(){
return ! path.isEmpty();
}
}
This class returns the signature bitmap.This view works fine for devices with Android 8.0 and below, but its not working for Android 8.0 plus devices. For Devices above Android 8.0, the method getBitmap() returns a bitmap of the signature, but for Devices above Android 8.0, it returns empty.
Another Solution I tried which did not work either
public class SignatureViewType3 extends View {
private Bitmap _Bitmap;
private Canvas _Canvas;
private Path _Path;
private Paint _BitmapPaint;
private Paint _paint;
private float _mX;
private float _mY;
private float TouchTolerance = 4;
private float LineThickness = 4;
private boolean signatureAdded;
public SignatureViewType3(Context context, AttributeSet attr) {
super(context, attr);
_Path = new Path();
_BitmapPaint = new Paint(Paint.DITHER_FLAG);
_paint = new Paint();
_paint.setAntiAlias(true);
_paint.setDither(true);
_paint.setColor(Color.argb(255, 0, 0, 0));
_paint.setStyle(Paint.Style.STROKE);
_paint.setStrokeJoin(Paint.Join.ROUND);
_paint.setStrokeCap(Paint.Cap.ROUND);
_paint.setStrokeWidth(LineThickness);
}
#Override
protected void onSizeChanged(int w, int h, int oldw, int oldh) {
super.onSizeChanged(w, h, oldw, oldh);
_Bitmap = Bitmap.createBitmap(w, (h > 0 ? h : ((View) this.getParent()).getHeight()), Bitmap.Config.ARGB_8888);
_Canvas = new Canvas(_Bitmap);
}
#Override
protected void onDraw(Canvas canvas) {
super.onDraw(canvas);
getParent().requestDisallowInterceptTouchEvent(true);
canvas.drawColor(Color.WHITE);
canvas.drawBitmap(_Bitmap, 0, 0, _BitmapPaint);
canvas.drawPath(_Path, _paint);
}
private void TouchStart(float x, float y) {
_Path.reset();
_Path.moveTo(x, y);
_mX = x;
_mY = y;
}
private void TouchMove(float x, float y) {
float dx = Math.abs(x - _mX);
float dy = Math.abs(y - _mY);
if (dx >= TouchTolerance || dy >= TouchTolerance) {
_Path.quadTo(_mX, _mY, (x + _mX) / 2, (y + _mY) / 2);
_mX = x;
_mY = y;
}
}
private void TouchUp() {
if (!_Path.isEmpty()) {
_Path.lineTo(_mX, _mY);
_Canvas.drawPath(_Path, _paint);
} else {
_Canvas.drawPoint(_mX, _mY, _paint);
}
signatureAdded = true;
_Path.reset();
}
#Override
public boolean onTouchEvent(MotionEvent e) {
super.onTouchEvent(e);
float x = e.getX();
float y = e.getY();
switch (e.getAction()) {
case MotionEvent.ACTION_DOWN:
TouchStart(x, y);
invalidate();
break;
case MotionEvent.ACTION_MOVE:
TouchMove(x, y);
invalidate();
break;
case MotionEvent.ACTION_UP:
TouchUp();
invalidate();
break;
}
return true;
}
public void clear() {
_Canvas.drawColor(Color.WHITE);
invalidate();
}
public byte[] getBytes() {
Bitmap b = getBitmap();
ByteArrayOutputStream baos = new ByteArrayOutputStream();
b.compress(Bitmap.CompressFormat.PNG, 100, baos);
if(signatureAdded)
return baos.toByteArray();
else
return null;
}
public Bitmap getBitmap() {
View v = (View) this.getParent();
Bitmap b = Bitmap.createBitmap(v.getWidth(), v.getHeight(), Bitmap.Config.ARGB_8888);
Canvas c = new Canvas(b);
v.layout(v.getLeft(), v.getTop(), v.getRight(), v.getBottom());
v.draw(c);
return b;
}
public boolean isDrawn(){
// return ! _Path.isEmpty();
return true;
}
}

getDrawingCache() is deprecated in Android API 28, so you should use Canvas like in this answer of Ashvin solanki
RelativeLayout view = (RelativeLayout)findViewById(R.id.relativelayout);
Bitmap bitmap = Bitmap.createBitmap(view.getWidth(), view.getHeight(), Bitmap.Config.ARGB_8888);
Canvas canvas = new Canvas(bitmap);
Drawable bgDrawable = view.getBackground();
if (bgDrawable != null) {
bgDrawable.draw(canvas);
} else {
canvas.drawColor(Color.WHITE);
}
view.draw(canvas);
or PixelCopy like in that article of Shivesh Karan Mehta:
// for api level 28
fun getScreenShotFromView(view: View, activity: Activity, callback: (Bitmap) -> Unit) {
activity.window?.let { window ->
val bitmap = Bitmap.createBitmap(view.width, view.height, Bitmap.Config.ARGB_8888)
val locationOfViewInWindow = IntArray(2)
view.getLocationInWindow(locationOfViewInWindow)
try {
if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {
PixelCopy.request(
window,
Rect(
locationOfViewInWindow[0],
locationOfViewInWindow[1],
locationOfViewInWindow[0] + view.width,
locationOfViewInWindow[1] + view.height
), bitmap, { copyResult ->
if (copyResult == PixelCopy.SUCCESS) {
callback(bitmap) }
else {
}
// possible to handle other result codes ...
},
Handler()
)
}
} catch (e: IllegalArgumentException) {
// PixelCopy may throw IllegalArgumentException, make sure to handle it
e.printStackTrace()
}
}
}

How to zoom canvas by two fingers and move?

I can draw by fingers in canvas, but I can not zoom it by two fingers without loss of scale drawn
and I want to do infinite my canvas size
I have this code:
public class MainActivity1 extends AppCompatActivity {
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(1000, 1000, 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;
}
}
}
Please give me advice how to do it?
And I also want to do infinite my canvas size - its optional.
Main problem is zoom

My advice - you can use opengl. It's looks like you want to create some drawer, but canvas not perfect solution for this. Currently almost all devices support opengl es. It faster than canvas and you can made many another function(as scaling, image pasting, 3d objects etc.) much more easier. Here you can find a good tutorial.

Yoo should use ScaleGestureDetector to scale your canvas. This is my sample code:
private class MyScaleGestureListener implements ScaleGestureDetector.OnScaleGestureListener {
public boolean onScale(ScaleGestureDetector detector) {
scaleFactor *= detector.getScaleFactor();
return true;
}
public boolean onScaleBegin(ScaleGestureDetector detector) {
Log.d("myZoomTag", "SCALE STARTED");
return true;
}
public void onScaleEnd(ScaleGestureDetector detector) {
Log.d("myZoomTag", "SCALE ENDED");
}
}
Here scaleFactor is global variable. In your onDraw method you should do something like this:
bitmapWidth *= scaleFactor;
bitmapHeight *= scaleFactor;

onDraw() or dispatchDraw() not getting called on touch

Code:
public class MainActivity extends AppCompatActivity implements GestureDetector.OnGestureListener,
GestureDetector.OnDoubleTapListener {
DrawView drawView;
private GestureDetectorCompat g1;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
drawView = new DrawView(this);
drawView.setBackgroundColor(Color.TRANSPARENT);
setContentView(drawView);
g1 = new GestureDetectorCompat(this,this);
g1.setOnDoubleTapListener(this);
}
#Override
public boolean onTouchEvent(MotionEvent event) {
g1.onTouchEvent(event);
return super.onTouchEvent(event);
}
#Override
public boolean onSingleTapConfirmed(MotionEvent e) {
DrawView.x_touch = e.getX();
DrawView.y_touch = e.getY();
Log.v("id2","message2");
return false;
}
Code for drawing:
public class DrawView extends View {
Paint paint = new Paint();
static float x_touch = -1;
static float y_touch = -1;
public DrawView(Context context) {
super(context);
super.setWillNotDraw(false);
paint.setColor(Color.BLACK);
}
#Override
public void onDraw(Canvas canvas) {
super.onDraw(canvas);
Display mdisp = ((WindowManager) getContext().getSystemService(Context.WINDOW_SERVICE)).getDefaultDisplay();
Point mdispSize = new Point();
mdisp.getSize(mdispSize);
int maxX = mdispSize.x;
int maxY = mdispSize.y;
canvas.drawLine(maxX/3, 0, maxX/3, maxY, paint);
canvas.drawLine(maxX*2/3, 0, maxX*2/3, maxY, paint);
canvas.drawLine(0, maxY/3, maxX, maxY/3, paint);
canvas.drawLine(0, maxY*2/3, maxX, maxY*2/3, paint);
Log.v("id1","message1");
if (x_touch>0 && y_touch > 0)
canvas.drawText("X",x_touch,y_touch,paint);
}
}
On doing some research I found that one need to call setWillNotDraw(false) while overriding onDraw() or use dispatchDraw().
I have tried both but Draw function is called only once.
I am new to android development.

Change your code as follow :
public class DrawView extends View {
Paint paint = new Paint();
float x_touch = -1;
float y_touch = -1;
public DrawView(Context context) {
super(context);
super.setWillNotDraw(false);
paint.setColor(Color.BLACK);
}
#Override
public void onDraw(Canvas canvas) {
super.onDraw(canvas);
Display mdisp = ((WindowManager) getContext().getSystemService(Context.WINDOW_SERVICE)).getDefaultDisplay();
Point mdispSize = new Point();
mdisp.getSize(mdispSize);
int maxX = mdispSize.x;
int maxY = mdispSize.y;
canvas.drawLine(maxX/3, 0, maxX/3, maxY, paint);
canvas.drawLine(maxX*2/3, 0, maxX*2/3, maxY, paint);
canvas.drawLine(0, maxY/3, maxX, maxY/3, paint);
canvas.drawLine(0, maxY*2/3, maxX, maxY*2/3, paint);
Log.v("id1","message1");
if (x_touch>0 && y_touch > 0)
canvas.drawText("X",x_touch,y_touch,paint);
}
public void setXandY(float x, float y) {
x_touch = x;
y_touch = y;
this.invalidate();
}
}
And :
#Override
public boolean onSingleTapConfirmed(MotionEvent e) {
drawView.setXandY(e.getX(), e.getY());
return (true);
}

Make movement more smooth

I'm trying to make this game app.
I basically have this BitMap bMapEgg moving down every time UpdateCourt() gets called in a Surfaceview ChickenView. The problem I'm facing is that it looks really chunky. The movement of the bitmap doesn't look smooth.
ballPosition.y += 18; is the code that makes it move.
Any ideas how to make it look smooth?
public class MainActivity extends Activity implements View.OnTouchListener{
static Canvas canvas;
static ChickenView chickenView;
//Used for getting display details like the number of pixels
static Display display;
static Point size;
static int screenWidth;
static int screenHeight;
static Point ballPosition;
static int ballWidth;
static boolean ballIsMovingDown;
//stats
static long lastFrameTime;
static int fps;
static int score;
static int lives;
static float bitmapPositionX ;
static float bitmapPositionY ;
static float bitmapWidth ;
static float bitmapHeight;
static Bitmap bMapEgg;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
chickenView = (ChickenView) findViewById(R.id.chickenView);
//Get the screen size in pixels
display = getWindowManager().getDefaultDisplay();
size = new Point();
if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.HONEYCOMB_MR2) {
display.getSize(size);
}
screenWidth = size.x;
screenHeight = size.y;
ballWidth = screenWidth / 35;
ballPosition = new Point();
ballPosition.x = screenWidth / 2;
ballPosition.y = 1 + ballWidth;
final ImageView imageEggs = (ImageView)findViewById(R.id.imageEggs);
final ImageView imageUpgrade = (ImageView)findViewById(R.id.imageUpgrade);
TextView test = (TextView)findViewById(R.id.textEggs);
imageUpgrade.setOnTouchListener(this);
chickenView.setOnTouchListener(this);
}
#Override
public boolean onTouch(View v, MotionEvent event) {
switch (v.getId()) {
case R.id.imageUpgrade:
if (event.getAction() == MotionEvent.ACTION_DOWN) {
final int x = (int) event.getX();
final int y = (int) event.getY();
//now map the coords we got to the
//bitmap (because of scaling)
ImageView imageView = ((ImageView)v);
Bitmap bitmap =((BitmapDrawable)imageView.getDrawable()).getBitmap();
int pixel = bitmap.getPixel(x,y);
//now check alpha for transparency
int alpha = Color.alpha(pixel);
if (alpha != 0) {
//do whatever you would have done for your click event here
Intent i;
i = new Intent(this, StructureActivity.class);
startActivity(i);
}
}
break;
case R.id.chickenView:
float x = event.getX();
float y = event.getY();
// Replace these with the correct values (bitmap x, y, width & height)
float x1 = bitmapPositionX;
float x2 = x1 + bitmapWidth;
float y1 = bitmapPositionY;
float y2 = y1 + bitmapHeight;
// Test to see if touch is inside the bitmap
if (x > x1 && x < x2 && y > y1 && y < y2) {
// Bitmap was touched
Log.v("test", "test");
} else {
Log.v("werkt ghil ni", "test");
}
break;
}
return true;
}
static class ChickenView extends SurfaceView implements Runnable {
Thread ourThread = null;
SurfaceHolder ourHolder;
volatile boolean playingSquash;
Paint paint;
public ChickenView(Context context) {
super(context);
init(context);
}
public ChickenView(Context context, AttributeSet attrs) {
super(context, attrs);
init(context);
}
public ChickenView(Context context, AttributeSet attrs, int defStyle) {
super(context, attrs, defStyle);
init(context);
}
private void init(Context context) {
ourHolder = getHolder();
paint = new Paint();
ballIsMovingDown = true;
}
#Override
public void run() {
while (playingSquash) {
updateCourt();
drawCourt();
controlFPS();
}
}
public void updateCourt() {
//depending upon the two directions we should be
//moving in adjust our x any positions
if (ballIsMovingDown) {
ballPosition.y += 18;
}
//if hits bottom
if (ballPosition.y > screenHeight - 7*ballWidth) {
ballIsMovingDown = false;
}
}
public void drawCourt() {
if (ourHolder.getSurface().isValid()) {
canvas = ourHolder.lockCanvas();
//Paint paint = new Paint();
canvas.drawColor(Color.BLACK);//the background
paint.setColor(Color.argb(255, 255, 255, 255));
paint.setTextSize(45);
canvas.drawText("Score:" + score + " Lives:" + lives + " fps:" + fps, 20, 40, paint);
Bitmap bMapEgg = BitmapFactory.decodeResource(getResources(), R.drawable.egg);
bMapEgg = scaleDown(bMapEgg,180, true);
Bitmap bMapBackground = BitmapFactory.decodeResource(getResources(), R.drawable.backgrounddd);
canvas.drawBitmap(bMapBackground, 0, 0, paint);
canvas.drawBitmap(bMapEgg, ballPosition.x, ballPosition.y, paint);
bitmapPositionX = ballPosition.x;
bitmapPositionY = ballPosition.y;
bitmapWidth = bMapEgg.getWidth();
bitmapHeight = bMapEgg.getHeight();
ourHolder.unlockCanvasAndPost(canvas);
}
}
public void controlFPS() {
long timeThisFrame = (System.currentTimeMillis() - lastFrameTime);
long timeToSleep = 15 - timeThisFrame;
if (timeThisFrame > 0) {
fps = (int) (1000 / timeThisFrame);
}
if (timeToSleep > 0) {
try {
ourThread.sleep(timeToSleep);
} catch (InterruptedException e) {
}
}
lastFrameTime = System.currentTimeMillis();
}
public void pause() {
playingSquash = false;
try {
ourThread.join();
} catch (InterruptedException e) {
}
}
public void resume() {
playingSquash = true;
ourThread = new Thread(this);
ourThread.start();
}
}
#Override
protected void onStop() {
super.onStop();
while (true) {
chickenView.pause();
break;
}
finish();
}
#Override
protected void onResume() {
super.onResume();
chickenView.resume();
}
#Override
protected void onPause() {
super.onPause();
chickenView.pause();
}
public boolean onKeyDown(int keyCode, KeyEvent event) {
if (keyCode == KeyEvent.KEYCODE_BACK) {
chickenView.pause();
finish();
return true;
}
return false;
}
public static Bitmap scaleDown(Bitmap realImage, float maxImageSize,
boolean filter) {
float ratio = Math.min(
(float) maxImageSize / realImage.getWidth(),
(float) maxImageSize / realImage.getHeight());
int width = Math.round((float) ratio * realImage.getWidth());
int height = Math.round((float) ratio * realImage.getHeight());
Bitmap newBitmap = Bitmap.createScaledBitmap(realImage, width,
height, filter);
return newBitmap;
}
}

The problem is that in each frame you decode and scale all bitmaps all over again.
Move your bitmaps decoding and scaling out of the draw method, put it in an initialization method and store decoded and scaled bitmaps in member variables (maybe even static ones) so you can just reuse them for drawing in each frame.

How can I erase my objects without Background Image?

I want to erase my bitmap but I don't want to erase background image. When I try to erase is white and it draw very hard in frames.
This is from CanvasView
erasePaint.setColor(Color.WHITE);
//erasePaint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.CLEAR));
erasePaint.setAntiAlias(true);
erasePaint.setStyle(Paint.Style.STROKE);
erasePaint.setStrokeJoin(Paint.Join.ROUND);
erasePaint.setStrokeWidth(12);
//....
protected void onDraw(Canvas canvas) {
paint.setPathEffect(null);
if(bitmap!=null){
for(MyEraser e:eraserList){
canvas.drawPath(e.p,erasePaint);
invalidate();
}
final OnTouchListener eraseListener = new OnTouchListener() {
public boolean onTouch(View v, MotionEvent event) {
// erasePaint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.CLEAR));
//FirstActivity.ll.setVisibility(LinearLayout.GONE);
switch (event.getAction()) {
case MotionEvent.ACTION_DOWN:
myEraser = new MyEraser();
lastTouchX = event.getX();
lastTouchY = event.getY();
myEraser.mouseDown(event.getX(), event.getY());
return true;
case MotionEvent.ACTION_MOVE:
case MotionEvent.ACTION_UP:
resetDirtyRect(event.getX(),event.getY());
int historySize = event.getHistorySize();
for(int i=0;i<historySize;i++){
float historicalX = event.getHistoricalX(i);
float historicalY = event.getHistoricalY(i);
expandDirtyRect(historicalX, historicalY);
myEraser.mouseUp(historicalX, historicalY);
}
myEraser.mouseUp(event.getX(), event.getY());
eraserList.add(myEraser);
break;
default:
Log.d("mock it up", "Unknown touch event " + event.toString());
return false;
}
invalidate(
(int) (dirtyRect.left - HALF_STROKE_WIDTH),
(int) (dirtyRect.top - HALF_STROKE_WIDTH),
(int) (dirtyRect.right + HALF_STROKE_WIDTH),
(int) (dirtyRect.bottom + HALF_STROKE_WIDTH));
lastTouchX = event.getX();
lastTouchY = event.getY();
return true;
}
};
}
}
This is MyEraser
public class MyEraser {
Paint paint = new Paint();
Path p = new Path();
public MyEraser(){
paint.setColor(Color.WHITE);
paint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.CLEAR));
paint.setStyle(Paint.Style.STROKE);
paint.setAntiAlias(true);
paint.setStrokeJoin(Paint.Join.ROUND);
paint.setStrokeWidth(5);
}
public void mouseDown(float x, float y) {
//path.addCircle(x,y,5,Path.Direction.CW);
p.moveTo( x, y );
// path.lineTo(x, y);
}
public void mouseMove(Path path, float x, float y) {
// path.addCircle(x,y,5,Path.Direction.CW);
}
public void mouseUp(float x, float y){
//path.addCircle(x,y,5,Path.Direction.CW);
p.lineTo(x, y);
}
public void draw(Canvas c,Path path){
//paint.setColor(Color.WHITE);
paint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.CLEAR));
paint.setStyle(Paint.Style.STROKE);
paint.setAntiAlias(true);
paint.setStrokeJoin(Paint.Join.ROUND);
paint.setStrokeWidth(7);
c.drawPath(p, paint);
}
}

EDIT: Started over for better explanation :)
I am not familiar with Android, in fact I have never used it. Use this code as an example of how to organize your code, rather than a functional code.
class MyView extends View {
private Eraser myEraser;
private Bitmap myBackgroundImage;
private Canvas myForegroundCanvas;
public MyView(Context context, Attributes, attrs) {
myEraser = new Eraser()
myBackgroundImage = BitmapFactory.decodeResource(getResources(), R.drawable.your_background_name);
Bitmap image = Bitmap.createBitmap(w, h, Bitmap.Config.ARGB_8888); // the width and height of the view
myForegroundCanvas = new Canvas(image);
}
public boolean onTouchEvent(MotionEvent event) {
// update your eraser path
return true;
}
protected void onDraw(Canvas canvas) {
canvas.drawBitmap(myBackgroundImage, 0, 0, null);
//for (Eraser item : eraserList) {
// if you have multiple eraser, add them to a list
myEraser.draw(myForegroundCanvas);
//}
canvas.drawCanvas(myForegroundCanvas, 0, 0, null);
}
}
The main idea is to keep the separation between your background and foreground images. That way, you could easily change the background and it would be updated. You could also have a reset on the foreground to erase everything, etc.
I hope this helps you.