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我是 qml 的新手，但我想通过参考 QT 示例的仪表板向 QQuickWidget 添加一个圆形仪表。下面是我的代码。

guagetest.pro

QT       += core gui
greaterThan(QT_MAJOR_VERSION, 4): QT += widgets quickwidgets
CONFIG += c++11

DEFINES += QT_DEPRECATED_WARNINGS

SOURCES += \
    main.cpp \
    mainwindow.cpp

HEADERS += \
    mainwindow.h

FORMS += \
    mainwindow.ui

# Default rules for deployment.
qnx: target.path = /tmp/$${TARGET}/bin
else: unix:!android: target.path = /opt/$${TARGET}/bin
!isEmpty(target.path): INSTALLS += target

RESOURCES += \
    dashboard.qrc

主窗口.cpp

#include "mainwindow.h"
#include "ui_mainwindow.h"

MainWindow::MainWindow(QWidget *parent)
    : QMainWindow(parent)
    , ui(new Ui::MainWindow)
{
    ui->setupUi(this);

    ui->quickWidget->setSource(QUrl("qrc:/qml/qml/test.qml"));
    ui->quickWidget->show();
}

MainWindow::~MainWindow()
{
    delete ui;
}

测试.qml

import QtQuick 2.2
import QtQuick.Window 2.1
import QtQuick.Controls 1.4
import QtQuick.Controls.Styles 1.4
import QtQuick.Extras 1.4

Item {
    id: container
    width: parent.width
    height: parent.height
    anchors.centerIn: parent.Center

    Row {
        id: gaugeRow
        spacing: container.width * 0.2
        anchors.centerIn: parent

        CircularGauge {
            id: speedometer
            value: valueSource.kph
            anchors.verticalCenter: parent.verticalCenter
            maximumValue: 280
            // We set the width to the height, because the height will always be
            // the more limited factor. Also, all circular controls letterbox
            // their contents to ensure that they remain circular. However, we
            // don't want to extra space on the left and right of our gauges,
            // because they're laid out horizontally, and that would create
            // large horizontal gaps between gauges on wide screens.
            width: height
            height: container.height * 0.8

            style: DashboardGaugeStyle {}
        }
    }
}

DashboardGaugeStyle.qml

import QtQuick 2.2
import QtQuick.Controls.Styles 1.4

CircularGaugeStyle {
    tickmarkInset: toPixels(0.04)       // gauge graduation radius
    minorTickmarkInset: tickmarkInset
    labelStepSize: 20                   // gauge graduation text
    labelInset: toPixels(0.23)          // gauge graduation text position

    property real xCenter: outerRadius
    property real yCenter: outerRadius
    property real needleLength: outerRadius - tickmarkInset * 1.25
    property real needleTipWidth: toPixels(0.02)
    property real needleBaseWidth: toPixels(0.06)
    property bool halfGauge: false

    function toPixels(percentage) {
        return percentage * outerRadius;
    }

    function degToRad(degrees) {
        return degrees * (Math.PI / 180);
    }

    function radToDeg(radians) {
        return radians * (180 / Math.PI);
    }

    function paintBackground(ctx) {
        if (halfGauge) {
            ctx.beginPath();
            ctx.rect(0, 0, ctx.canvas.width, ctx.canvas.height / 2);
            ctx.clip();
        }

        ctx.beginPath();
        ctx.fillStyle = "black";
        ctx.ellipse(0, 0, ctx.canvas.width, ctx.canvas.height);
        ctx.fill();

        ctx.beginPath();
        ctx.lineWidth = tickmarkInset;
        ctx.strokeStyle = "black";
        ctx.arc(xCenter, yCenter, outerRadius - ctx.lineWidth / 2, outerRadius -ctx.lineWidth / 2, 0, Math.PI * 2);
        ctx.stroke();

        ctx.beginPath();
        ctx.lineWidth = tickmarkInset / 2;
        ctx.strokeStyle = "#222";
        ctx.arc(xCenter, yCenter, outerRadius - ctx.lineWidth / 2, outerRadius -ctx.lineWidth / 2, 0, Math.PI * 2);
        ctx.stroke();

        ctx.beginPath();
        var gradient = ctx.createRadialGradient(xCenter, yCenter, 0, xCenter, yCenter, outerRadius * 1.5);
        gradient.addColorStop(0, Qt.rgba(1, 1, 1, 0));
        gradient.addColorStop(0.7, Qt.rgba(1, 1, 1, 0.13));
        gradient.addColorStop(1, Qt.rgba(1, 1, 1, 1));
        ctx.fillStyle = gradient;
        ctx.arc(xCenter, yCenter, outerRadius - tickmarkInset, outerRadius - tickmarkInset, 0, Math.PI * 2);
        ctx.fill();
    }

    background: Canvas {
        onPaint: {
            var ctx = getContext("2d");
            ctx.reset();
            paintBackground(ctx);
        }

        Text {
            id: speedText
            font.pixelSize: toPixels(0.3)
            text: kphInt
            color: "white"
            horizontalAlignment: Text.AlignRight
            anchors.horizontalCenter: parent.horizontalCenter
            anchors.top: parent.verticalCenter
            anchors.topMargin: toPixels(0.1)

            readonly property int kphInt: control.value
        }
        Text {
            text: "km/h"
            color: "white"
            font.pixelSize: toPixels(0.09)
            anchors.top: speedText.bottom
            anchors.horizontalCenter: parent.horizontalCenter
        }
    }

    needle: Canvas {
        implicitWidth: needleBaseWidth
        implicitHeight: needleLength

        property real xCenter: width / 2
        property real yCenter: height / 2

        onPaint: {
            var ctx = getContext("2d");
            ctx.reset();

            ctx.beginPath();
            ctx.moveTo(xCenter, height);
            ctx.lineTo(xCenter - needleBaseWidth / 2, height - needleBaseWidth / 2);
            ctx.lineTo(xCenter - needleTipWidth / 2, 0);
            ctx.lineTo(xCenter, yCenter - needleLength);
            ctx.lineTo(xCenter, 0);
            ctx.closePath();
            ctx.fillStyle = Qt.rgba(0.66, 0, 0, 0.66);
            ctx.fill();

            ctx.beginPath();
            ctx.moveTo(xCenter, height)
            ctx.lineTo(width, height - needleBaseWidth / 2);
            ctx.lineTo(xCenter + needleTipWidth / 2, 0);
            ctx.lineTo(xCenter, 0);
            ctx.closePath();
            ctx.fillStyle = Qt.lighter(Qt.rgba(0.66, 0, 0, 0.66));
            ctx.fill();
        }
    }

    foreground: null
}

当我编译时，出现以下消息。

qrc:/qml/qml/test.qml:9: TypeError: Cannot read property 'width' of null
qrc:/qml/qml/test.qml:10: TypeError: Cannot read property 'height' of null
qrc:/qml/qml/test.qml:20: ReferenceError: valueSource is not defined
qrc:/qml/qml/test.qml:11: TypeError: Cannot read property 'Center' of null

我想知道为什么会出现该消息以及如何解决它。 以及如何更改 QQuickWidget 的背景颜色？

请帮我。

4

1 回答 1

1

根对象需要一个初始大小。并且不需要以父母为中心，因为没有父母。假设尺寸为 500x300。

Item {
    id: container
    width: 500
    height: 300

或者，如果您不想给出恒定大小，但childrenRect可以使用完全适合内容的大小。确保您的内容大小不依赖于根目录并且在使用前具有有效的宽度和高度。它可能会导致“检测到宽度/高度的绑定循环”。警告。

Item {
    id: container
    width: childrenRect.width
    height: childrenRect.height

如果您希望您的场景根据 QQuickWidget 的大小调整大小，请动态设置调整大小模式。

ui->quickWidget->setResizeMode(QQuickWidget::SizeRootObjectToView);

让我们进入着色点。要更改根项目的颜色，我们可以使用Rectangle.color属性。因此，将根对象从 Item 更改为 Rectangle。让我们将背景设为红色。

Rectangle {
    id: container
    width: childrenRect.width
    height: childrenRect.height
    color: "red"

或者如果你想改变 QQuickWidget 的窗口颜色，设置调色板。但既然你的场景会覆盖它，我怀疑这就是你所需要的。

auto palette = ui->quickWidget->palette();
palette.setColor(QPalette::Window, QColor(Qt::red));
ui->quickWidget->setPalette(palette);

你还有一个问题：

qrc:/qml/qml/test.qml:20: ReferenceError: valueSource is not defined

我不知道是什么valueSource，要么确保你拥有它，要么摆脱它。

于 2021-01-29T16:21:59.927 回答