在自定义图纸视图中，撤消和重做选项不起作用

Question

我正在尝试在自定义绘图视图应用程序中创建 undo,redo 选项。但它没有按我的意愿工作。

我英语不好。通过图片，让我尝试展示undo、redo函数的工作原理。希望如此，这张照片将解释我的问题。

我想在第一次撤消单击时删除第一行，在第二次撤消单击时删除第二行，依此类推...类似地，在重做单击时，在第一次单击时绘制最后一行，在第二次单击时删除倒数第二行，依此类推..

这是我的自定义视图类。

public class DrawingView extends View{

    ArrayList<Path> undoPath = new ArrayList<Path>();
    ArrayList<Path> paths    = new ArrayList<Path>();
    private static int pathSize =0;
    //draw path
    private Path drawPath;
    //drawing and canvas point
    private Paint drawPaint, canvasPaint;
    //initial color
    private int paintColor=0xFF660000;
    //canvas
    private Canvas drawCanvas;
    //canvas bitmap
    private Bitmap canvasBitmap;

    private float brushSize, lastBrushSize; 

    public DrawingView(Context context, AttributeSet attrs) {
        super(context, attrs);
        setupDrawing();
    }
    public void setPattern(String newPattern){
        invalidate();
        int patternID = getResources().getIdentifier(newPattern, "drawable", "com.faisalahsan.paintingapp");
        Bitmap patternBMP = BitmapFactory.decodeResource(getResources(), patternID);
        BitmapShader patternBMPShader = new BitmapShader(patternBMP, Shader.TileMode.REPEAT, Shader.TileMode.REPEAT);
        drawPaint.setColor(0xFFFFFFFF);
        drawPaint.setShader(patternBMPShader);

    }
    private void setupDrawing(){
        //get drawing area setup for interaction
        drawPath = new Path();
        drawPaint= new Paint();

        paths.add(drawPath);

        brushSize = getResources().getInteger(R.integer.medium_size);
        lastBrushSize = brushSize;

        drawPaint.setColor(paintColor);
        drawPaint.setAntiAlias(true);
        drawPaint.setStrokeWidth(brushSize);
        drawPaint.setStyle(Paint.Style.STROKE);
        drawPaint.setStrokeJoin(Paint.Join.ROUND);
        drawPaint.setStrokeCap(Paint.Cap.ROUND);

        canvasPaint = new Paint(Paint.DITHER_FLAG);     
    }

    @Override
    protected void onDraw(Canvas canvas) {          
        for(Path p: paths){         
            canvas.drawBitmap(canvasBitmap, 0,  0, canvasPaint);
            canvas.drawPath(p, drawPaint);          
        }
    }

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

    }

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

       public void onClickRedo (){
        if (undoPath.size()>0)  {
         paths.add(undoPath.remove(undoPath.size()-1));         
         invalidate();
         }
        }


    @Override
    public boolean onTouchEvent(MotionEvent event) {

        float touchX = event.getX();
        float touchY = event.getY();

        switch (event.getAction()) {
        case  MotionEvent.ACTION_DOWN:
            drawPath.moveTo(touchX, touchY);
            break;          
        case MotionEvent.ACTION_MOVE:
            drawPath.lineTo(touchX, touchY);            
            break;
        case  MotionEvent.ACTION_UP:
            drawCanvas.drawPath(drawPath, drawPaint);
            drawPath.reset();
            drawPath = new Path();
            paths.add(drawPath);
            break;
        default:
            return false;
        }
        invalidate();
        return true;        
    }   
}

Answer 1

当“撤消”从 ArrayList“路径”中删除操作时，您不是在画布上“重绘” - 换句话说，将其从列表中取出不会更改图像。您必须在绘制之前重新绘制画布上的内容才能“撤消”操作。

在“onDraw”启动时保存画布的状态，然后在调用撤消时重绘该画布。您需要保持画布状态的同步堆栈，以便执行一系列“撤消”和“重做”调用。