QML 和 QQuickWidget

问题描述

我是qml的新手，但我想通过参考QT示例的仪表板向QQuickWidget添加一个圆规。 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

mainwindow.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;
} 

test.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,ctx.canvas.width,ctx.canvas.height / 2);
            ctx.clip();
        }

        ctx.beginPath();
        ctx.fillStyle = "black";
        ctx.ellipse(0,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,Math.PI * 2);
        ctx.stroke();

        ctx.beginPath();
        ctx.linewidth = tickmarkInset / 2;
        ctx.strokeStyle = "#222";
        ctx.arc(xCenter,Math.PI * 2);
        ctx.stroke();

        ctx.beginPath();
        var gradient = ctx.createradialGradient(xCenter,xCenter,outerRadius * 1.5);
        gradient.addColorStop(0,Qt.rgba(1,1,0));
        gradient.addColorStop(0.7,0.13));
        gradient.addColorStop(1,1));
        ctx.fillStyle = gradient;
        ctx.arc(xCenter,outerRadius - tickmarkInset,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(0.66,0.66);
            ctx.fill();

            ctx.beginPath();
            ctx.moveto(xCenter,height)
            ctx.lineto(width,height - needleBaseWidth / 2);
            ctx.lineto(xCenter + needleTipwidth / 2,0);
            ctx.closePath();
            ctx.fillStyle = Qt.lighter(Qt.rgba(0.66,0.66));
            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这条消息以及如何解决。 以及如何更改 QQuickWidget 的背景颜色？

请帮帮我。

解决方法

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

Item {
    id: container
    width: 500
    height: 300

或者，如果您不想给出一个恒定的大小，而是使大小完全适合内容，则可以使用 childrenRect。在使用之前，请确保您的内容大小不依赖于 root 并且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。但由于您的场景将涵盖它，我怀疑这是否是您所需要的。

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

还有一个问题：

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

我不知道 valueSource 是什么，要么确保你拥有它，要么摆脱它。