property int keyboardModifiers: Qt.NoModifier Item { focus: true Keys.onPressed: { keyboardModifiers = Qt.keyboardModifiers } Keys.onReleased: { keyboardModifiers = Qt.NoModifier } }这个函数未能正确使用，报错原因是Error: Cannot assign [undefined] to int

这个错误提示表明 keyboardModifiers 在某些情况下未能被正确赋值，因此在尝试将 undefined 赋值给 int 类型的属性时出现了错误。

这可能是因为在未按下任何键时，Qt.keyboardModifiers 返回的是 undefined。为了避免这个问题，你可以在属性定义时为 keyboardModifiers 指定一个默认值，例如：

property int keyboardModifiers: Qt.NoModifier

Item {
    focus: true

    Keys.onPressed: {
        keyboardModifiers = Qt.keyboardModifiers || Qt.NoModifier
    }
    Keys.onReleased: {
        keyboardModifiers = Qt.NoModifier
    }
}

这个代码片段中使用了逻辑或运算符，如果 Qt.keyboardModifiers 返回 undefined，则使用 Qt.NoModifier 作为默认值。这样可以确保 keyboardModifiers 总是被正确赋值。

如果问题依然存在，请检查你的键盘事件是否正确设置并且键盘焦点是否被正确分配。

相关问题

我的qt版本是5.13.2，无法正确使用keyboardModifiers，给出的报错信息是ReferenceError: keyboardModifiers is not defined，报错程序是import QtQuick 2.12 import QtQuick.Window 2.12 Window { visible: true width: 640 height: 480 title: qsTr("Hello World") Rectangle { width: 200 height: 200 color: "lightgray" Text { text: "Press and hold the Shift key" anchors.centerIn: parent } Rectangle { width: 100 height: 100 color: "red" MouseArea { anchors.fill: parent onClicked: { if (keyboardModifiers & Qt.ShiftModifier) { console.log("Shift key is pressed") } else { console.log("Shift key is not pressed") } } } } } }

从错误信息来看，似乎是 keyboardModifiers 未被定义。这个问题通常出现在引入 QtQuick 时，因为 keyboardModifiers 并不是 QtQuick 组件的一部分。

你可以通过在 import 语句中添加 QtQuick.Controls 2.0 来解决这个问题。这个组件库中包含了一些常用组件，包括 MouseArea，同时也定义了 keyboardModifiers。

下面是修改后的代码示例：

import QtQuick 2.12
import QtQuick.Window 2.12
import QtQuick.Controls 2.0

Window {
    visible: true
    width: 640
    height: 480
    title: qsTr("Hello World")

    Rectangle {
        width: 200
        height: 200
        color: "lightgray"

        Text {
            text: "Press and hold the Shift key"
            anchors.centerIn: parent
        }

        Rectangle {
            width: 100
            height: 100
            color: "red"

            MouseArea {
                anchors.fill: parent

                onClicked: {
                    if (keyboardModifiers & Qt.ShiftModifier) {
                        console.log("Shift key is pressed")
                    } else {
                        console.log("Shift key is not pressed")
                    }
                }
            }
        }
    }
}

注意：如果你在使用 Qt Quick 1.x，这个解决方法可能会不起作用。在这种情况下，你需要手动定义 keyboardModifiers。在你的代码中添加以下内容即可：

property int keyboardModifiers: Qt.NoModifier
Item {
    focus: true
    Keys.onPressed: {
        keyboardModifiers = Qt.keyboardModifiers
    }
    Keys.onReleased: {
        keyboardModifiers = Qt.NoModifier
    }
}

这会在你的代码中创建一个新的属性 keyboardModifiers，通过捕捉按键事件并使用 Qt.keyboardModifiers 来更新它。

Use c # to complete the following code,Creating a Car class A class is a self-contained piece of software that is able to function on it own. We will model a car in software. Car Class Properties Year : int «private set» Manufacturer : string «private set» Model : string «private set» IsDrivable : bool «private set» Price : double «private set» Methods«constructor» Car(year : int, manufacturer : string, model : string, price : double, isDrivable: bool = true) PrintInfo() : void Description of field members: 1. year: this private member represents the year value of this object 2. manufacturer: this private member represents the manufacturer of this car 3. model: this private member represents the model of this car 4. isDrivable: this private member indicates if this car be driven 5. price: this private member represents the selling price of this car Constructor: 1. public Car(int year, string manufacturer, string model, double price, bool isDrivable = true): this is the constructor of this class. It takes five arguments and assigns them to the appropriate fields. You will assume that all the arguments will be sane (i.e. the values will not break your program). Apology: UML and some newer languages specify the type after the identifier. C# on the other hand requires that you specify the type and then the identifier. To restrict access fields are normally decorated with the private modifier. Programming II Car: fields, constructor, ToString() n.k.p Page 2 of 2 Description of action member: 1. public void PrintInfo(): this method does not take any argument but it will print all information about this object. You get to decide how the output will look like. It is expected that all the values be displayed. In your main method write the code to do the following: 1. Create at least four cars and print them. Remember to call the constructor with 4 or 5 parameters.

Here's the code to create a Car class in C#:

using System;

class Car
{
    private int year;
    private string manufacturer;
    private string model;
    private bool isDrivable;
    private double price;

    public Car(int year, string manufacturer, string model, double price, bool isDrivable = true)
    {
        this.year = year;
        this.manufacturer = manufacturer;
        this.model = model;
        this.price = price;
        this.isDrivable = isDrivable;
    }

    public void PrintInfo()
    {
        Console.WriteLine("Year: " + year);
        Console.WriteLine("Manufacturer: " + manufacturer);
        Console.WriteLine("Model: " + model);
        Console.WriteLine("Is Drivable: " + isDrivable);
        Console.WriteLine("Price: " + price);
    }
}

In your main method, you can create four Car objects and print their information like this:

static void Main(string[] args)
{
    Car car1 = new Car(2021, "Toyota", "Camry", 25000.0);
    Car car2 = new Car(2019, "Honda", "Civic", 20000.0, false);
    Car car3 = new Car(2018, "Ford", "Mustang", 35000.0);
    Car car4 = new Car(2020, "Tesla", "Model S", 80000.0);

    car1.PrintInfo();
    car2.PrintInfo();
    car3.PrintInfo();
    car4.PrintInfo();
}

This will output the information for all four cars.