撤消重做功能不起作用

Question

我正在为android用户开发一款绘图应用程序。我想在我的应用程序上实现撤消重做功能。我引用stackoverflow上发布的问题来解决我的问题，但我无法为我的代码找到正确的解决方案。下面我发布了我的代码，请帮助我解决这个问题。如有任何帮助，我们将不胜感激。

提前谢谢。

public class DrawingView extends View {
 private ArrayList<Path> paths = new ArrayList<Path>();
 private ArrayList<Path> undonePaths = new ArrayList<Path>(); 
public DrawingView(Context context, AttributeSet attrs) {
    super(context, attrs);
    // TODO Auto-generated constructor stub
    this.context = context;
    setupDrawing();
}
public void setupDrawing(){
    drawPath = new Path();
    drawPaint = new Paint();
    canvasPaint = new Paint(Paint.DITHER_FLAG);
    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);
    paths.add(drawPath);
}
@Override
protected void onSizeChanged(int w, int h, int oldw, int oldh) {
//view given size
    super.onSizeChanged(w, h, oldw, oldh);
    canvasBitmap = Bitmap.createBitmap(w, h, Bitmap.Config.ARGB_8888);
    drawCanvas = new Canvas(canvasBitmap);
}
@Override
protected void onDraw(Canvas canvas) {
    //draw view
    canvas.drawBitmap(canvasBitmap, 0, 0, canvasPaint);
    canvas.drawPath(drawPath, drawPaint);
    for(Path p : paths){
        canvas.drawPath(p, drawPaint);
    }
}
@Override
public boolean onTouchEvent(MotionEvent event) {
    float touchX = event.getX();
    float touchY = event.getY();
    switch (event.getAction()) {
    case MotionEvent.ACTION_DOWN:
    //  undonePaths.clear();
        drawPath.moveTo(touchX, touchY);
        break;
    case MotionEvent.ACTION_MOVE:
        drawPath.lineTo(touchX, touchY);
        break;
    case MotionEvent.ACTION_UP:
    //  drawPath.lineTo(touchX, touchY);
        drawCanvas.drawPath(drawPath, drawPaint);
        drawPath.reset();
        drawPath = new Path();
        paths.add(drawPath);  
        break;
    default:
        return false;
    }
    invalidate();
    return true;   
}

public void onClickUndo(){
    if(paths.size()>0){
        undonePaths.add(paths.remove(paths.size() - 1));
        Toast.makeText(getContext(), "Undo is working", Toast.LENGTH_LONG).show();
        invalidate();
    }
    else{
        Toast.makeText(getContext(), "Undo is not working", Toast.LENGTH_LONG).show();
    }
}
public void onClickRedo(){
    if(undonePaths.size()>0){
        paths.add(undonePaths.remove(undonePaths.size() - 1));
        Toast.makeText(getContext(), "Redo is working", Toast.LENGTH_LONG).show();
        invalidate();
    }
    else{
        Toast.makeText(getContext(), "Redo is not working", Toast.LENGTH_LONG).show();
    }
}
}

Answer 1

只是一些小改动。

在您的列表中有一个额外的Path，它将导致"撤消/重做"步骤在其余部分得到纠正时基本上什么都不做。所以在setupDrawing()中删除：

paths.add(drawPath);

在onDraw()方法中，删除：

canvas.drawBitmap(canvasBitmap, 0, 0, canvasPaint);

此drawBitmap()调用正在重新绘制在每个ACTION_UP上绘制到的成员位图，使其看起来好像您的Path列表没有更新一样。

然后在onTouchEvent()方法中，在MotionEvent.ACTION_DOWN中取消注释：

undonePaths.clear();

并将MotionEvent.ACTION_UP的情况更改为：

case MotionEvent.ACTION_UP:
    drawCanvas.drawPath(drawPath, drawPaint);
    paths.add(drawPath);  
    drawPath = new Path();
    break;

reset()调用正在清除您不想要的Path。相反，在这里，我们将最近完成的Path添加到列表中，然后创建一个新的来继续。

注意：按照目前的工作方式，撤消/恢复功能不会影响canvasBitmap。由于不清楚这个位图是用来做什么的，所以我保持原样。如果你想让这个位图镜像视图的，你可以简单地将drawCanvas.drawPath()调用移动到onDraw()，与那里的canvas.drawPath()调用并行。

Answer 2

var undoRedo = new Array();
var unStep = -1;
function historySave() {
    unStep++;
    while (undoRedo.length > 20) {
        undoRedo.shift();
        unStep--;
    }
    if (unStep !== 0 && unStep < undoRedo.length) {
        undoRedo.length = unStep;
        unStep++;
    } else {
        undoRedo.length = unStep;
    }
    undoRedo.push(document.getElementById('drawingCanvas').toDataURL());    
}
function Undo() {
    if (unStep > -1) {
        unStep--;
        var canvasPic = new Image();
        canvasPic.src = undoRedo[unStep];
        drawingContext.clearRect(0,0,drawingCanvas.width,drawingCanvas.height);
        canvasPic.onload = function () {
        drawingContext.drawImage(canvasPic, 0, 0);
            }
    }
}
function Redo() {
    if (unStep < undoRedo.length - 1) {
        unStep++;
        var canvasPic = new Image();
        canvasPic.src = undoRedo[unStep];
        canvasPic.onload = function ()  { 
        drawingContext.drawImage(canvasPic, 0, 0);
        }
    }
}