安卓FingerPaint Undo/Redo实现

Question

我正在做一个测试项目，类似于Android SDK Demos中的FingerPaint示例。我试图在我的项目中实现undo/redo功能，但我尝试的东西并没有像我期望的那样工作。我在网上和这里发现了一些类似的问题，但它们对我没有帮助，这就是为什么我要问一个新的问题。

下面是我实际在做的一些想法：

    public class MyView extends View {

    //private static final float MINP = 0.25f;
    //private static final float MAXP = 0.75f;



    private Path    mPath;
    private Paint   mBitmapPaint;

    public MyView(Context c) {
        super(c);

        mPath = new Path();
        mBitmapPaint = new Paint(Paint.DITHER_FLAG);

    }

    @Override
    protected void onSizeChanged(int w, int h, int oldw, int oldh) {
        super.onSizeChanged(w, h, oldw, oldh);
        mBitmap = Bitmap.createBitmap(w, h, Bitmap.Config.ARGB_8888);

        mCanvas = new Canvas(mBitmap);
        mCanvas.drawColor(Color.WHITE);
    }

    @Override
    protected void onDraw(Canvas canvas) {
        canvas.drawColor(Color.WHITE);
        canvas.drawBitmap(mBitmap, 0, 0, mBitmapPaint);

        canvas.drawPath(mPath, 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.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;
    }
}

有什么建议/想法/示例是在我的项目中实现这种功能的最佳方式吗？

Answer 1

我不知道这是不是你想要的，但这就是我正在做的。而不是只将其存储在一个路径中，而是存储一个包含所有路径的数组，就像这样，用户可以绘制许多线条，只需稍加修改，您也可以添加多点触控。

要进行撤消和重做，只需从paths变量中删除或添加最后一个路径路径，并将它们存储在一个新的数组中。类似于：

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 
}

这是我修改过的面板，我现在不能尝试它，但是上面的方法应该可以工作！希望它能帮上忙！(有几个额外的变量，只需删除它们:)

private ArrayList<Path> undonePaths = new ArrayList<Path>(); 
public class DrawingPanel extends View implements OnTouchListener {

private Canvas  mCanvas;
private Path    mPath;
private Paint   mPaint,circlePaint,outercirclePaint;   
private ArrayList<Path> paths = new ArrayList<Path>();
private ArrayList<Path> undonePaths = new ArrayList<Path>(); 
private float xleft,xright,xtop,xbottom;

public DrawingPanel(Context context) {
    super(context);
    setFocusable(true);
    setFocusableInTouchMode(true);

    this.setOnTouchListener(this);


    circlePaint = new Paint();
    mPaint = new Paint();
    outercirclePaint = new Paint();
    outercirclePaint.setAntiAlias(true);
    circlePaint.setAntiAlias(true);
    mPaint.setAntiAlias(true);        
    mPaint.setColor(0xFFFFFFFF);
    outercirclePaint.setColor(0x44FFFFFF);
    circlePaint.setColor(0xAADD5522);
    outercirclePaint.setStyle(Paint.Style.STROKE);
    circlePaint.setStyle(Paint.Style.FILL);        
    mPaint.setStyle(Paint.Style.STROKE);
    mPaint.setStrokeJoin(Paint.Join.ROUND);
    mPaint.setStrokeCap(Paint.Cap.ROUND);
    mPaint.setStrokeWidth(6);
    outercirclePaint.setStrokeWidth(6);        
    mCanvas = new Canvas();
    mPath = new Path();
    paths.add(mPath);             


    cx = 400*DrawActivity.scale;
    cy = 30*DrawActivity.scale;
    circleRadius = 20*DrawActivity.scale;
    xleft = cx-10*DrawActivity.scale;
    xright = cx+10*DrawActivity.scale;
    xtop = cy-10*DrawActivity.scale;
    xbottom = cy+10*DrawActivity.scale;

}


public void colorChanged(int color) {
    mPaint.setColor(color);
}


    @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 = 0;

    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);
    }



@Override
public boolean onTouch(View arg0, MotionEvent event) {
      float x = event.getX();
      float y = event.getY();

      switch (event.getAction()) {
          case MotionEvent.ACTION_DOWN:
              if (x <= cx+circleRadius+5 && x>= cx-circleRadius-5) {
                  if (y<= cy+circleRadius+5 && cy>= cy-circleRadius-5){
                      paths.clear();
                      return true;
                      }
              }
              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;
}




}

Answer 2

最好的解决方案是实现自己的撤销/重做引擎。

1. 将您在数组中执行的每个操作保存到数组中(即x1，y1，1 line from x2，y2 to x3，y3等)
2. draw
3. 如果需要撤消，请清除画布并重绘所有n-1操作，从to n-1
4. 如果要撤消更多操作，只需从to n-2等

进行绘制

我希望它能给你一个提示

干杯!

Answer 3

实现do/redo功能的一种方法是将方法调用和调用所需的所有信息封装在一个对象中，以便您可以存储它并在以后调用它- Command Pattern。

在此模式中，每个操作都有自己的对象: DrawCircleCommand、DrawPathCommand、FillColorCommand等。在每个对象中，draw()方法以一种独特的方式实现，但始终被称为draw(Canvas canvas)，这允许CommandManager迭代命令。要撤消，需要遍历调用undo()方法的对象；

每个命令对象实现一个接口

public interface IDrawCommand {  
  public void draw(Canvas canvas);  
  public void undo();  
}  

对象将如下所示：

public class DrawPathCommand implements IDrawCommand{  
  public Path path;  
  public Paint paint;  

  public void setPath(path){
    this.path = path
  }

  public void draw(Canvas canvas) {  
    canvas.drawPath( path, paint );  
  }  

  public void undo() {  
   //some  action to remove the path
 }  

}

您的命令将添加到CommandManager中：

mCommandManager.addCommand(IDrawCommand command)

要撤消一个命令，您只需调用：

mCommandManager.undo();

CommandManager将命令存储在数据结构中，例如允许其在命令对象上迭代的列表。

你可以找到一个完整的教程here，关于如何在Android上使用画布绘图的do/undo来实现命令模式。

Here是关于如何在Java语言中实现命令模式的另一个教程；