import QtQuick 2.4 import QtQuick.Controls 2.5 import QtQuick.Window 2.3 ApplicationWindow { visible: true width: 800 height: 600 title: "Drawing Board Example" Item { width: 400 height: 400 property int gridSize: 20 property int scaleFactor: 100 Canvas { id: canvas anchors.fill: parent onPaint: { var ctx = getContext("2d"); var width = canvas.width; var height = canvas.height; // 清除画布 ctx.clearRect(0, 0, width, height); // 绘制网格线 ctx.strokeStyle = "black"; for (var x = 0; x <= width; x += gridSize) { ctx.beginPath(); ctx.moveTo(x, 0); ctx.lineTo(x, height); ctx.stroke(); } for (var y = 0; y <= height; y += gridSize) { ctx.beginPath(); ctx.moveTo(0, y); ctx.lineTo(width, y); ctx.stroke(); } } } MouseArea { anchors.fill: parent // wheelEnabled: true onWheel: { // 根据滚轮事件的delta属性，计算缩放比例 scaleFactor += wheel.angleDelta.y / 120; scaleFactor = Math.max(scaleFactor, 10); // 最小值为10% canvas.width = width * scaleFactor / 100; canvas.height = height * scaleFactor / 100; canvas.requestPaint(); } } } }这段代码不能够成功实现可伸缩的网格画布，应该如何优化

这段代码中的问题在于，缩放时只改变了canvas的宽度和高度，但是没有改变gridSize，导致网格线的间距没有随之缩放。为了实现可伸缩的网格画布，可以在缩放时同时改变gridSize和canvas的宽度和高度，使得网格线的间距也跟着缩放。修改后的代码如下：

import QtQuick 2.4
import QtQuick.Controls 2.5
import QtQuick.Window 2.3

ApplicationWindow {
    visible: true
    width: 800
    height: 600
    title: "Drawing Board Example"

    Item {
        width: 400
        height: 400

        property int gridSize: 20
        property int scaleFactor: 100

        Canvas {
            id: canvas
            anchors.fill: parent

            onPaint: {
                var ctx = getContext("2d");
                var width = canvas.width;
                var height = canvas.height;

                // 清除画布
                ctx.clearRect(0, 0, width, height);

                // 绘制网格线
                ctx.strokeStyle = "black";
                for (var x = 0; x <= width; x += gridSize) {
                    ctx.beginPath();
                    ctx.moveTo(x, 0);
                    ctx.lineTo(x, height);
                    ctx.stroke();
                }
                for (var y = 0; y <= height; y += gridSize) {
                    ctx.beginPath();
                    ctx.moveTo(0, y);
                    ctx.lineTo(width, y);
                    ctx.stroke();
                }
            }
        }

        MouseArea {
            anchors.fill: parent
            onWheel: {
                // 根据滚轮事件的delta属性，计算缩放比例
                scaleFactor += wheel.angleDelta.y / 120;
                scaleFactor = Math.max(scaleFactor, 10); // 最小值为10%

                // 根据缩放比例重新计算gridSize和canvas的宽度和高度
                gridSize = scaleFactor / 5;
                canvas.width = width * scaleFactor / 100;
                canvas.height = height * scaleFactor / 100;

                canvas.requestPaint();
            }
        }
    }
}

在这段代码中，我们在缩放时通过计算缩放比例来同时改变gridSize和canvas的宽度和高度，从而实现了可伸缩的网格画布。