There are multiple scribble apps on here that have an undo button. I haven't implemented those because my code is different, but I have looked at the concepts. I.E storing points in an array.
When the program detects touch events:
@Override
public boolean onTouchEvent(MotionEvent event) {
float touchX = event.getX(); //Gets the fingers x position
float touchY = event.getY(); //gets the fingers y position
PointF points = new PointF(); //init a new PointF
points.x = touchX; //store the coordinates in the Point object
points.y = touchY;
_pointList.add(points); //add this to the list of Points (array)
switch (event.getAction()){
case MotionEvent.ACTION_DOWN:
_path.moveTo(touchX, touchY); //Set the beginning of the next contour to the point (x,y)
//will start drawing from where the last point was
break;
case MotionEvent.ACTION_MOVE:
_path.lineTo(touchX, touchY);
break;
case MotionEvent.ACTION_UP:
break;
}
invalidate();
return true;
}
In theory the _pointList Array should capture all the touch inputs in order. And this is evident, since the console displays the size of the array.
In the onDraw method, it should loop through all of the points in the a_pointList List. Since it contains all of the points that the user has interacted on the screen, then in theory it should draw the lines from memory.
@Override
protected void onDraw(Canvas canvas) {
super.onDraw(canvas);
for (PointF points : _pointList) {
_path.moveTo(points.x, points.y);
_path.lineTo(points.x, points.y);
_canvas.drawPath(_path, _paint);
}
canvas.drawBitmap(_bitmap, 0, 0, _paint);
}
When the application runs I am able to draw on the screen, and due to the clear method the screen clears.
public void clear(){
_pointList.clear();// empty the list that stores the points
_bitmap = Bitmap.createBitmap(1000,1000,
Bitmap.Config.ARGB_8888);
_canvas = new Canvas(_bitmap);
_path = new Path();
_paint = new Paint(Paint.DITHER_FLAG);
//Added later..
_paint.setColor(Color.RED);
_paint.setAntiAlias(true);
_paint.setStyle(Paint.Style.STROKE);
//empties the screen
invalidate();
}
However, in my undo method, it should drop one of the points (that contains the users X and Y touch inputs) from the _pointList List. After dropping the point, the screen should redraw all of the lines from memory.
public void undo() {
Log.d("Number", "undo:" + _pointList.size() );
if (_pointList.size()>0){
_bitmap = Bitmap.createBitmap(1000,1000,
Bitmap.Config.ARGB_8888);
_canvas = new Canvas(_bitmap);
_path = new Path();
_paint = new Paint(Paint.DITHER_FLAG);
//Added later..
_paint.setColor(Color.RED);
_paint.setAntiAlias(true);
_paint.setStyle(Paint.Style.STROKE);
_pointList.remove(_pointList.size() - 1);
invalidate();
}
}
This method has the same effect as the 'clear' method and does not redraw the lines,
My other alternatives to the undo button was putting the bitmaps into an array, but I'm sure that would cause memory issues since it's a dynamic program.
Question: Why doesn't the 'invalidate' call from the 'undo' method update the screen?
Update:
The whole code:
--Draw--
package com.example.moynul.myapplication;
import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.graphics.Path;
import android.graphics.Point;
import android.graphics.PointF;
import android.graphics.PorterDuff;
import android.util.AttributeSet;
import android.util.Log;
import android.view.MotionEvent;
import android.view.View;
import android.widget.Button;
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
/**
* Created by moynu on 10/12/2015.
*/
public class Draw extends View {
private Paint _paint = new Paint();
private Path _path = new Path();
private Bitmap _bitmap;
private Canvas _canvas;
private List<PointF> _pointList = new ArrayList<PointF>();
public Draw(Context context) {
super(context);
init(null, 0);
}
public Draw(Context context, AttributeSet attrs) {
super(context, attrs);
init(attrs,0);
}
public Draw(Context context, AttributeSet attrs, int defStyleAttr) {
super(context, attrs, defStyleAttr);
init(attrs, defStyleAttr);
}
private void init(AttributeSet attrs, int defStyleAttr) {
_paint.setColor(Color.RED);
_paint.setAntiAlias(true);
_paint.setStyle(Paint.Style.STROKE);
_bitmap = Bitmap.createBitmap (1080, 1920, Bitmap.Config.ARGB_8888);
_canvas = new Canvas(_bitmap);
}
@Override
public boolean onTouchEvent(MotionEvent event) {
float touchX = event.getX(); //Gets the fingers x position
float touchY = event.getY(); //gets the fingers y position
PointF points = new PointF(); //init a new PointF
points.x = touchX; //store the coordinates in the Point object
points.y = touchY;
_pointList.add(points); //add this to the list of Points (array)
switch (event.getAction()){
case MotionEvent.ACTION_DOWN:
_path.moveTo(touchX, touchY); //Set the beginning of the next contour to the point (x,y)
//will start drawing from where the last point was
break;
case MotionEvent.ACTION_MOVE:
_path.lineTo(touchX, touchY);
break;
case MotionEvent.ACTION_UP:
break;
}
invalidate();
return true;
}
@Override
protected void onDraw(Canvas canvas) {
super.onDraw(canvas);
for (PointF points : _pointList) {
_path.moveTo(points.x, points.y);
_path.lineTo(points.x, points.y);
_canvas.drawPath(_path, _paint);
}
canvas.drawBitmap(_bitmap, 0, 0, _paint);
}
public void clear(){
_pointList.clear();// empty the list that stores the points
_bitmap = Bitmap.createBitmap(1000,1000,
Bitmap.Config.ARGB_8888);
_canvas = new Canvas(_bitmap);
_path = new Path();
_paint = new Paint(Paint.DITHER_FLAG);
//Added later..
_paint.setColor(Color.RED);
_paint.setAntiAlias(true);
_paint.setStyle(Paint.Style.STROKE);
//empties the screen
invalidate();
}
public void undo() {
Log.d("Number", "undo:" + _pointList.size());
if (_pointList.size()>0){
_pointList.remove(_pointList.size() - 1);
_bitmap = Bitmap.createBitmap(1000,1000,
Bitmap.Config.ARGB_8888);
_canvas = new Canvas(_bitmap);
_path = new Path();
_paint = new Paint(Paint.DITHER_FLAG);
//Added later..
_paint.setColor(Color.RED);
_paint.setAntiAlias(true);
_paint.setStyle(Paint.Style.STROKE);
invalidate();
}
}
}
