Question

I am using a customized version of FingerPaint for Android with some other features, like inserting images and moving them. I decided to implement an Undo&Redo, since it will make life just easier. In order to implement it, I finally decided to use a Stack where I push the Drawing Cache of the view, and from where I push the content every time I want to go back to a previous state. So, using the FingerPaint as a basis, I have the following:

private void touch_up() {
    mPath.lineTo(mX, mY);
    // commit the path to our offscreen
    mCanvas.drawPath(mPath, mPaint);
    // I enable the set drawing cache...       
    myView.setDrawingCacheEnabled(true);
    // ... and I add the cache to the stack
    undoStack.add(myView.getDrawingCache());
    indexOfUndoRedo++;
    // kill this so we don't double draw
    mPath.reset();
} 

The stack is being updated only after the touch up at the moment, since I am still figuring out how to solve this. When I want to apply redo, I do the following:

private void undo() {
    myView = new MyView(getActivity());
    myView.setBackgroundDrawable(new BitmapDrawable(undoStack.get(indexOfUndoRedo)));
    indexOfUndoRedo--;
    myView.invalidate();
} 

So far, the application shows the original state of the screen with no change. I also tried to paint it with a white background in order to reset it, but this approach is also not working.

Any idea or suggestion on how to fix this? I would be really thankful 🙂

Regards

Answer 1

Try below code Draw View:

package com.draw;
import java.util.ArrayList;
import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.graphics.Canvas;
import android.graphics.Paint;
import android.graphics.Path;

import android.view.MotionEvent;
import android.view.View;
import android.view.View.OnTouchListener;
import android.widget.ImageView;

public class DrawView extends View implements OnTouchListener {
    private Canvas  mCanvas;
    private Path    mPath;
    private Paint       mPaint;   
    private ArrayList<Path> paths = new ArrayList<Path>();
    private ArrayList<Path> undonePaths = new ArrayList<Path>(); 

    private Bitmap im;
    public DrawView(Context context) 
    {
        super(context);
        setFocusable(true);
        setFocusableInTouchMode(true);      
        this.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();
        paths.add(mPath);

        im=BitmapFactory.decodeResource(context.getResources(),R.drawable.ic_launcher);


    }               
        @Override
        protected void onSizeChanged(int w, int h, int oldw, int oldh) {
            super.onSizeChanged(w, h, oldw, oldh);
        }

        @Override
        protected void onDraw(Canvas canvas) {            

            for (Path p : paths){
                canvas.drawPath(p, mPaint);
            }
        }

        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
            mCanvas.drawPath(mPath, mPaint);
            // kill this so we don't double draw            
            mPath = new Path();
            paths.add(mPath);
        }

        public void onClickUndo () { 
            if (paths.size()>0) 
            { 
               undonePaths.add(paths.remove(paths.size()-1));
               invalidate();
             }
            else
            {

            }
             //toast the user 
        }

        public void onClickRedo (){
           if (undonePaths.size()>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;
    }
}

and Draw Activity layout code below:

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:orientation="vertical" >
 <FrameLayout android:id="@+id/main_frame"
     android:layout_width="fill_parent" android:layout_height="250dp">

 </FrameLayout>
        <Button
        android:id="@+id/button2"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Redo" />

    <Button
        android:id="@+id/button1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Undo" />

</LinearLayout>

and Draw Activity Class below code:

package com.draw;

import android.app.Activity;
import android.os.Bundle;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.FrameLayout;
import android.widget.ImageButton;
import android.widget.ImageView;
import android.widget.LinearLayout;
import android.widget.Toast;

public class Draw extends Activity {
     ImageView iv1;
    @Override   
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        final DrawView drawView = new DrawView(this);
        setContentView(R.layout.main);
        FrameLayout frm_layout=(FrameLayout) findViewById(R.id.main_frame);
        frm_layout.addView(drawView);
        Button btn_undo=(Button) findViewById(R.id.button1);
        btn_undo.setOnClickListener(new OnClickListener() {

            @Override
            public void onClick(View v) {
                // TODO Auto-generated method stub
                drawView.onClickUndo();
            }
        });

        Button btn_redo=(Button) findViewById(R.id.button2);
        btn_redo.setOnClickListener(new OnClickListener() {

            @Override
            public void onClick(View v) {
                // TODO Auto-generated method stub
                drawView.onClickRedo();
            }
        });
    }

}

This is sample paint app with undo and redo operations in android,it work’s perfectly for me!