How to clear drawings on Canvas in Android… here is a solution to the problem.
How to clear drawings on Canvas in Android
I’ve set up Canvas for the drawing. My question now is how to clear the drawing.
Trying to do this won’t help.
public void clear()
{
circlePath.reset();
mPath.reset();
Calls the onDraw() method
invalidate();
}
Please see the entire code here:
https://gist.github.com/akosijiji/a29cca90bead2e5e35ad
Any help is greatly appreciated.
Solution
Click the button
b1.setOnClickListener(new OnClickListener()
{
@Override
public void onClick(View v) {
TODO Auto-generated method stub
dv.clear(); call clear method using in your custom view
}
});
Define a clear method in a custom View
public void clear()
{
mBitmap = Bitmap.createBitmap(width,height ,
Bitmap.Config.ARGB_8888);
mCanvas = new Canvas(mBitmap);
mPath = new Path();
mBitmapPaint = new Paint(Paint.DITHER_FLAG);
Added later..
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);
invalidate();
}
Reset all drawing tools and invoke invalidation to refresh the View.
Complete working code
public class MainActivity extends Activity implements ColorPickerDialog.OnColorChangedListener {
DrawingView dv ;
RelativeLayout rl;
private Paint mPaint;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
dv = new DrawingView(this);
setContentView(R.layout.activity_main);
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);
rl = (RelativeLayout) findViewById(R.id.rl);
rl.addView(dv);
Button b = (Button) findViewById(R.id.button1);
b.setText(R.string.France);
Button b1 = (Button) findViewById(R.id.button2);
rl.setDrawingCacheEnabled(true);
b.setOnClickListener(new OnClickListener()
{
@Override
public void onClick(View v) {
TODO Auto-generated method stub
dv.clear();
new ColorPickerDialog(MainActivity.this, MainActivity.this, mPaint.getColor()).show();
}
});
b1.setOnClickListener(new OnClickListener()
{
@Override
public void onClick(View v) {
TODO Auto-generated method stub
dv.clear();
}
});
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.activity_main, menu);
return true;
}
public class DrawingView extends View {
private int width;
private 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);
width =w;
height =h;
mBitmap = Bitmap.createBitmap(w, h, Bitmap.Config.ARGB_8888);
mCanvas = new Canvas(mBitmap);
}
public void clear()
{
mBitmap = Bitmap.createBitmap(width,height ,
Bitmap.Config.ARGB_8888);
Log.d("BITMAP","Restoring...");
mBitmap=BitmapFactory.decodeByteArray(bytes, 0, bytes.length);
mCanvas = new Canvas(mBitmap);
mPath = new Path();
mBitmapPaint = new Paint(Paint.DITHER_FLAG);
Added later..
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);
invalidate();
}
@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);
invalidate();
}
}
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();
mPaint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.SCREEN));//. Mode.SCREEN));
mPaint.setMaskFilter(null);
mCanvas.drawColor(Color.TRANSPARENT, PorterDuff.Mode.SCREEN);
}
@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;
}
}
@Override
public void colorChanged(int color) {
TODO Auto-generated method stub
mPaint.setColor(color);
}
}
The above works, but it’s not good for design, because every time you need to clear you will create objects like paint objects.
You can create a singleton class and reset your tool, then call invalidate
public class DrawingManager {
private static DrawingManager mInstance=null;
public DrawingTools mDrawingUtilities=null;
public int mThemeIndex;
public Canvas mCanvas;
public Path mPath;
public Paint mBitmapPaint;
public Bitmap mBitmap;
public Paint mPaint;
private DrawingManager()
{
resetDrawingTools();
}
public static DrawingManager getInstance()
{
if(mInstance==null)
{
mInstance=new DrawingManager();
}
return mInstance;
}
public void resetDrawingTools()
{
mBitmap = Bitmap.createBitmap(screenwidth,screenheight ,
Bitmap.Config.ARGB_8888)
mCanvas = new Canvas(mBitmap);
Path = new Path();
mBitmapPaint = new Paint(Paint.DITHER_FLAG);
Added later..
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);
}
/**
* Clears the drawing board.
*/
public static void clearDrawingBoard()
{
mInstance=null;
}
public void resetBitmapCanvasAndPath() {
TODO Auto-generated method stub
mBitmap = Bitmap.createBitmap(screenwidth,screenheight ,
Bitmap.Config.ARGB_8888);
Log.d("BITMAP","Restoring...");
mBitmap=BitmapFactory.decodeByteArray(bytes, 0, bytes.length);
mCanvas = new Canvas(.mBitmap);
mPath = new Path();
}
}
In your drawing class
private DrawingManager mDrawingManager=null;
mDrawingManager=DrawingManager.getInstance();// initialize drawing tools once
Then tap Clear Drawing on the button
mDrawingManager.resetBitmapCanvasAndPath();
invalidate();