java - 在 JavaFX 中实现撤消/重做

Question

我正在尝试在 JavaFX 中实现撤消/重做 - 我使用 graphicsContext() 绘制所有形状。我环顾四周，发现 Graphics Context 上有一个 save 方法，但它只是保存属性，而不是 Canvas 的实际形状/状态。解决这个问题的最佳方法是什么？

这是我创建圆圈时的代码片段之一，例如:

 public CircleDraw(Canvas canvas, Scene scene, BorderPane borderPane) {
        this.borderPane = borderPane;
        this.scene = scene;
        this.graphicsContext = canvas.getGraphicsContext2D();

        ellipse = new Ellipse();
        ellipse.setStrokeWidth(1.0);
        ellipse.setFill(Color.TRANSPARENT);
        ellipse.setStroke(Color.BLACK);

        pressedDownMouse = event -> {
            startingPosX = event.getX();
            startingPosY = event.getY();
            ellipse.setCenterX(startingPosX);
            ellipse.setCenterY(startingPosY);
            ellipse.setRadiusX(0);
            ellipse.setRadiusY(0);
            borderPane.getChildren().add(ellipse);

        };

        releasedMouse = event -> {
            borderPane.getChildren().remove(ellipse);
            double width = Math.abs(event.getX() - startingPosX);
            double height = Math.abs(event.getY() - startingPosY);
            graphicsContext.setStroke(Color.BLACK);
            graphicsContext.strokeOval(Math.min(startingPosX, event.getX()),    Math.min(startingPosY, event.getY()), width, height);
        removeListeners();
        };

        draggedMouse = event -> {
            ellipse.setCenterX((event.getX() + startingPosX) / 2);
            ellipse.setCenterY((event.getY() + startingPosY) / 2);
            ellipse.setRadiusX(Math.abs((event.getX() - startingPosX) / 2));
            ellipse.setRadiusY(Math.abs((event.getY() - startingPosY) / 2));

        };

    }

Answer 1

这里的问题是像这样的信息没有保存在 Canvas 中。此外，没有逆向操作可以让您返回到每个抽奖信息的先前状态。当然，您可以描画相同的椭圆形，但使用背景颜色，但是之前绘图信息中的信息可能已被覆盖，例如如果您正在绘制多个相交的椭圆。

不过，您可以使用命令模式存储绘图操作。这使您可以重绘所有内容。

public interface DrawOperation {
    void draw(GraphicsContext gc);
}

public class DrawBoard {
    private final List<DrawOperation> operations = new ArrayList<>();
    private final GraphicsContext gc;
    private int historyIndex = -1;

    public DrawBoard(GraphicsContext gc) {
        this.gc = gc;
    }

    public void redraw() {
        Canvas c = gc.getCanvas();
        gc.clearRect(0, 0, c.getWidth(), c.getHeight());
        for (int i = 0; i <= historyIndex; i++) {
            operations.get(i).draw(gc);
        }
    }

    public void addDrawOperation(DrawOperation op) {
        // clear history after current postion
        operations.subList(historyIndex+1, operations.size()).clear();

        // add new operation
        operations.add(op);
        historyIndex++;
        op.draw(gc);
    }

    public void undo() {
        if (historyIndex >= 0) {
            historyIndex--;
            redraw();
        }
    }

    public void redo() {
        if (historyIndex < operations.size()-1) {
            historyIndex++;
            operations.get(historyIndex).draw(gc);
        }
    }
}

class EllipseDrawOperation implements DrawOperation {

    private final double minX;
    private final double minY;
    private final double width;
    private final double height;
    private final Paint stroke;

    public EllipseDrawOperation(double minX, double minY, double width, double height, Paint stroke) {
        this.minX = minX;
        this.minY = minY;
        this.width = width;
        this.height = height;
        this.stroke = stroke;
    }

    @Override
    public void draw(GraphicsContext gc) {
        gc.setStroke(stroke);
        gc.strokeOval(minX, minY, width, height);
    }

}

将 DrawBoard 实例而不是 Canvas 传递给您的类并替换

graphicsContext.setStroke(Color.BLACK);
graphicsContext.strokeOval(Math.min(startingPosX, event.getX()),    Math.min(startingPosY, event.getY()), width, height);

与

drawBoard.addDrawOperation(new EllipseDrawOperation(
                             Math.min(startingPosX, event.getX()),
                             Math.min(startingPosY, event.getY()),
                             width,
                             height,
                             Color.BLACK));

undo 和 redo 在历史中移动。