Qt是一個跨平臺框架，通常用作圖形工具包，它不僅創(chuàng)建CLI應(yīng)用程序中非常有用。而且它也可以在三種主要的臺式機(jī)操作系統(tǒng)以及移動操作系統(tǒng)（如Symbian，Nokia Belle，Meego Harmattan，MeeGo或BB10）以及嵌入式設(shè)備，Android（Necessitas）和iOS的端口上運(yùn)行?，F(xiàn)在我們?yōu)槟闾峁┝嗣赓M(fèi)的試用版。趕快點(diǎn)擊下載Qt最新試用版吧>>

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在本文的第1部分中，我們展示了如何在Visual Studio中針對Windows和嵌入式Linux創(chuàng)建多平臺Qt Quick應(yīng)用程序項(xiàng)目?，F(xiàn)在，我們將展示如何在嵌入式設(shè)備上運(yùn)行該應(yīng)用程序。然后，我們將繼續(xù)將該項(xiàng)目開發(fā)為我們打算創(chuàng)建的完整嵌入式應(yīng)用程序。最后，我們將使用VS調(diào)試器對應(yīng)用程序的C ++和QML代碼進(jìn)行遠(yuǎn)程調(diào)試。

在嵌入式設(shè)備上運(yùn)行

我們已經(jīng)展示了如何交叉編譯在Visual Studio中創(chuàng)建的“ hello world” Qt Quick應(yīng)用程序。現(xiàn)在，我們將看到如何在Raspberry Pi上運(yùn)行該應(yīng)用程序。由于我們將以全屏模式運(yùn)行，因此我們必須首先向應(yīng)用程序窗口中添加一些內(nèi)容。

Window {
    visible: true
    title: qsTr("Hello World")
    Text {
        id: clock
        font.pointSize: 72
        Timer {
            interval: 1000; running: true; repeat: true
            onTriggered: clock.text = (new Date).toLocaleTimeString(Qt.locale("de_DE"), "hh:mm:ss");
        }
    }
}

和以前一樣，選擇Linux項(xiàng)目配置，然后按F7鍵開始交叉編譯。

1>------ Build started: Project: QuickMirror, Configuration: Debug_RPi x64 ------
1>rcc qml.qrc
1>Invoking 'mkdir -p $(dirname qml.qrc); mkdir -p $(dirname /mnt/c/Users/user/Source/Repos/QuickMirror/main.qml); mkdir -p $(dirname /mnt/c/Users/user/Source/Repos/QuickMirror/obj/x64/Debug_RPi/rcc/qrc_qml.cpp); (/home/user/raspi/qt5/bin/rcc /mnt/c/Users/user/Source/Repos/QuickMirror/qml.qrc --name qml -o /mnt/c/Users/user/Source/Repos/QuickMirror/obj/x64/Debug_RPi/rcc/qrc_qml.cpp)', working directory: '/mnt/c/Users/user/Source/Repos/QuickMirror'
1>Starting remote build
1>Compiling sources:
1>qrc_qml.cpp
1>Linking objects
1>QuickMirror.vcxproj -> C:\Users\user\Source\Repos\QuickMirror\bin\x64\Debug_RPi\QuickMirror.out
========== Build: 1 succeeded, 0 failed, 0 up-to-date, 0 skipped ==========

要在每次構(gòu)建結(jié)束時自動復(fù)制應(yīng)用程序文件，可以在“ WSL構(gòu)建后事件”屬性頁中設(shè)置以下命令（ATTN： 這將以明文形式保存設(shè)備密碼）。

C:\Users\user> scp C:\Users\user\Source\Repos\QuickMirror\bin\x64\Debug_RPi\QuickMirror.out pi@192.168.1.98:/home/pi/

pi@192.168.1.98's password:

QuickMirror.out 100% 465KB 1.6MB/s 00:00

C:\Users\user>

在啟動Qt Quick應(yīng)用程序之前，我們需要設(shè)置一些必需的環(huán)境變量：

• LD_LIBRARY_PATH
  Qt二進(jìn)制文件安裝目錄的路徑。
  
  
• QT_QPA_PLATFORM
  平臺插件。
  
  
• QT_QPA_PLATFORM_PLUGIN_PATH
  平臺插件安裝目錄的路徑。
  
  
• QT_QPA_EGLFS_PHYSICAL_WIDTH
  QT_QPA_EGLFS_PHYSICAL_HEIGHT
  物理屏幕的寬度和高度，以毫米為單位。
  
  
• QML2_IMPORT_PATH
  安裝的QML模塊的路徑。

pi@raspberry-pi:~$ export LD_LIBRARY_PATH="/usr/local/qt5pi/lib"
pi@raspberry-pi:~$ export QT_QPA_PLATFORM="eglfs"
pi@raspberry-pi:~$ export QT_QPA_PLATFORM_PLUGIN_PATH="/usr/local/qt5pi/plugins/platforms"
pi@raspberry-pi:~$ export QT_QPA_EGLFS_PHYSICAL_WIDTH="326"
pi@raspberry-pi:~$ export QT_QPA_EGLFS_PHYSICAL_HEIGHT="520"
pi@raspberry-pi:~$ export QML2_IMPORT_PATH="/usr/local/qt5pi/qml"
pi@raspberry-pi:~$ ./QuickMirror.out

樹莓派顯示器

在Raspberry Pi中運(yùn)行“ Hello World”應(yīng)用程序

開發(fā)應(yīng)用程序

我們的應(yīng)用程序的要求包括顯示以下信息：

• 當(dāng)前時間
• 當(dāng)前日期
• 周年紀(jì)念
• 天氣預(yù)報
• 下次出發(fā)的公共交通工具
• 新聞

我們將把每個項(xiàng)目封裝為專用的QML類型。為此，我們必須首先將QML模塊定義（qmldir）文件添加到項(xiàng)目中：

• 選擇“項(xiàng)目>添加新項(xiàng)。。> Qt> QML模塊定義”。
• 在位置字段中，指示將包含QML文件的文件夾的路徑。

向項(xiàng)目添加新的QML模塊定義

按下“添加”后，qmldir 文件將在項(xiàng)目樹中可用。我們將使用此文件來定義每種QML類型到其對應(yīng)源文件的映射。

ApiCall         1.0 QuickMirror.ApiCall.qml
Calendar        1.0 QuickMirror.Calendar.qml
Clock           1.0 QuickMirror.Clock.qml
NewsTicker      1.0 QuickMirror.NewsTicker.qml
OnThisDay       1.0 QuickMirror.OnThisDay.qml
PublicTransport 1.0 QuickMirror.PublicTransport.qml
Weather         1.0 QuickMirror.Weather.qml

要將新的QML源文件添加到項(xiàng)目中：

• 選擇“項(xiàng)目>添加新項(xiàng)...> Qt> QML文件”。
• 將位置設(shè)置qmldir為創(chuàng)建文件的相同目錄。
• 設(shè)置QML文件名。
• 按“添加”。

我們將首先添加QML類型以顯示當(dāng)前時間，當(dāng)前日期和重要的周年紀(jì)念日。該Clock類型將顯示當(dāng)前時間，每秒刷新一次。

QuickMirror.Clock.qml

  function refresh() {
        text = (new Date).toLocaleTimeString(Qt.locale("de_DE"), "hh:mm");
    }
    Component.onCompleted : refresh();
    Timer {
        interval: 1000; running: true; repeat: true onTriggered: parent.refresh();
    }
} 

該Calendar類型將顯示當(dāng)前日期，并在不同語言環(huán)境之間循環(huán)。

QuickMirror.Calendar.qml

Text {
    renderType: Text.NativeRendering
    id: calendar
    color: "white"
    font.family: FontFamily_Bold
    font.styleName: FontStyle_Bold
    font.pointSize: 72
    property var locales: ["en_US", "de_DE", "pt_PT"]
    property var localeIdx: 0
    function capitalize(s) {
        return s.replace(/(^|-)./g, function(c) { return c.toUpperCase(); });
    }
    function setNextLocale() {
        localeIdx = (localeIdx + 1) % locales.length;
    }
    function getCurrentText() {
        var date = new Date;
        var locale = Qt.locale(locales[localeIdx]);
        var calendarText = capitalize(date.toLocaleDateString(locale, "dddd, dd"));
        var monthShort = date.toLocaleDateString(locale, "MMM");
        var monthLong = date.toLocaleDateString(locale, "MMMM");
        if (monthLong.length <= 5) { calendarText += capitalize(monthLong); } else { calendarText += capitalize(monthShort); if (!monthShort.endsWith(".")) calendarText += "."; } calendarText += date.toLocaleDateString(locale, " yyyy"); return calendarText; } Component.onCompleted: { text = getCurrentText(); } Timer { interval: 15000; running: true; repeat: true onTriggered: { setNextLocale(); text = getCurrentText(); } } Behavior on text { SequentialAnimation { NumberAnimation { target: calendar; property: "opacity"; to: 0.0; duration: 1000 } PropertyAction { target: calendar; property: "text" } NumberAnimation { target: calendar; property: "opacity"; to: 1.0; duration: 500 } } } }

除了日期/時間，我們的應(yīng)用程序還將依靠Web API來檢索信息。我們將curl在一個單獨(dú)的過程中運(yùn)行以連接到Web API。流程創(chuàng)建將由名為的C ++類處理Process。然后，QML類型ApiCall將使用一個Process對象以curl必要的參數(shù)開始并收集其輸出。

QuickMirror.ApiCall.qml

Item {
    property var url: ""
    property var path: []
    property var query: []
    signal response(var response)
    signal error(var error)
    Process {
        id: curl
        property var path: Q_OS_WIN ? "C:\\Windows\\System32\\curl.exe" : "/usr/bin/curl"
        property var request: ""
        command: path + " -s \"" + request + "\""
    }
    function sendRequest() {
        curl.request = url;
        if (path.length > 0)
            curl.request += "/" + path.join("/");
         if (query.length > 0)
            curl.request += "?" + query.join("&");
        curl.start();
    }
    Connections {
        target: curl
        onExit /*(int exitCode, QByteArray processOutput)*/ : {
            if (exitCode != 0) {
                console.log("ApiCall: exit " + exitCode);
                console.log("==== ApiCall: request: " + curl.request);
                return error("exit " + exitCode);
            }
            try {
                return response(JSON.parse(processOutput));
            } catch (err) {
                console.log("ApiCall: error: " + err.toString());
                console.log("==== ApiCall: request: " + curl.request);
                console.log("==== ApiCall: response: " + processOutput);
                return error(err);
            }
        }
    }
}

要創(chuàng)建ProcessC ++類：

• 選擇“項(xiàng)目>添加Qt類> Qt類”
• 將類名設(shè)置為Process
• 按“添加”

class Process : public QProcess
{
    Q_OBJECT
    Q_PROPERTY(QString command READ command WRITE setCommand NOTIFY commandChanged)

public:
    Process(QObject* parent = 0);
    ~Process();

public:
    Q_INVOKABLE void start();
    void setCommand(const QString& cmd);
    QString command() const;

signals:
    void commandChanged();
    void exit(int exitCode, QByteArray processOutput);

protected:
    void onFinished(int exitCode, QProcess::ExitStatus status);
    void onErrorOccurred(QProcess::ProcessError error);

private:
    QString m_command;
};

Process.cpp

Process(QObject* parent) : QProcess(parent)
{
    connect(
        this, QOverload::of(&QProcess::finished),
        this, &Process::onFinished);
    connect(
        this, &QProcess::errorOccurred,
        this, &Process::onErrorOccurred);
}

Process::~Process()
{
}

void Process::setCommand(const QString& cmd)
{
    if (cmd != m_command) {
        m_command = cmd;
        emit commandChanged();
    }
}

QString Process::command() const
{
    return m_command;
}

void Process::start()
{
    if (state() == ProcessState::NotRunning)
        QProcess::start(m_command);
    else
        qInfo() << "==== QProcess: ERROR already running:" << m_command; } void Process::onFinished(int exitCode, QProcess::ExitStatus status) { emit exit((status == ExitStatus::NormalExit) ? exitCode : -1, readAll()); } void Process::onErrorOccurred(QProcess::ProcessError error) { qInfo() << "==== QProcess: ERROR " << error; }

main.cpp

int main(int argc, char* argv[])
{
    qmlRegisterType("Process", 1, 0, "Process");
...

該OnThisDay QML類型將使用的實(shí)例，通過它們來獲取顯著的紀(jì)念日列表和循環(huán)每隔幾秒鐘。 ApiCall

QuickMirror.OnThisDay.qml

Item {
    id: onThisDay
    clip: true
    property int viewportHeight
    property var events: []
    property var births: []
    property var deaths: []
    property int idxEventType: -1
    ApiCall {
        id: onThisDayApi
        property int month: 0
        property int day: 0
        property string eventType: ""
        url: "http://byabbe.se"; path: ["on-this-day", month, day, eventType + ".json" ]
        onResponse: {
            if ("events" in response) {
                events = shuffle(response.events);
                eventType = "births";
                sendRequest();
            } else if ("births" in response) {
                births = shuffle(response.births);
                for (var i in births)
                    births[i].year = "*" + births[i].year;
                eventType = "deaths";
                sendRequest();
            } else if ("deaths" in response) {
                deaths = shuffle(response.deaths);
                for (var i in deaths)
                    deaths[i].year = "?" + deaths[i].year;
                next();
            }
        }
    }
    function init() {
        events = [];
        births = [];
        deaths = [];
        idxEventType = -1;
        var today = new Date;
        onThisDayApi.month = today.getMonth() + 1;
        onThisDayApi.day = today.getDate();
        onThisDayApi.eventType = "events";
        onThisDayApi.sendRequest();
    }
    function next() {
        if (events.length + births.length + deaths.length == 0)
            return;
        var today = new Date;
        if (onThisDayApi.month != today.getMonth() + 1 || onThisDayApi.day != today.getDate())
            return init();
        onThisDayText.color = "white";
        idxEventType = (idxEventType + 1) % 3;
        var event;
        switch (idxEventType) {
            case 0:
                if (events.length == 0)
                    return next();
                event = events.shift();
                events = shuffle(events);
                events.push(event);
                break;
            case 1:
                if (births.length == 0)
                    return next();
                event = births.shift();
                births = shuffle(births);
                births.push(event);
                break;
            case 2:
                if (deaths.length == 0)
                    return next();
                event = deaths.shift();
                deaths = shuffle(deaths);
                deaths.push(event);
                break;
        }
        onThisDayText.text = event.year + " – " + event.description;
        showText.start();
    }
    Component.onCompleted: {
        init();
    }
    Timer {
        id: timerRetry
        interval: 10000; running: true; repeat: true
        onTriggered: {
            if (events.length + births.length + deaths.length == 0)
                init();
        }
    }
    SequentialAnimation {
        id: showText
        PropertyAction { target: onThisDayText; property: "y"; value: 25 }
        NumberAnimation { target: onThisDayText; property: "opacity"; to: 1.0; duration: 500 }
        PauseAnimation { duration: 3000 }
        NumberAnimation {
            target: onThisDayText
            property: "y"
            to: Math.min(-(25 + onThisDayText.contentHeight) + viewportHeight, 25)
            duration: Math.max(0, (Math.abs(to - from) * 1000) / 25)
        }
        PauseAnimation { duration: 3000 }
        NumberAnimation { target: onThisDayText; property: "opacity"; to: 0.0; duration: 1000 }
        onFinished: {
            onThisDay.next();
        }
    }
    Text {
        renderType: Text.NativeRendering
        id: onThisDayText
        wrapMode: Text.WordWrap
        font.family: FontFamily_Normal
        font.styleName: FontStyle_Normal
        font.pointSize: 40
        textFormat: Text.RichText
        color: "white"
        y: 25
        anchors.left: parent.left
        width: parent.width
        height: contentHeight
        opacity: 0
    }
    Rectangle {
        id: top
        anchors.top: parent.top
        anchors.left: parent.left
        width: parent.width
        height: 10
        gradient: Gradient {
            orientation: Gradient.Vertical
            GradientStop { position: 0.0; color: "black" }
            GradientStop { position: 0.5; color: "transparent" }
        }
    }
    Rectangle {
        id: bottomFade
        anchors.top: parent.top
        anchors.topMargin: viewportHeight
        anchors.left: parent.left
        width: parent.width
        height: 0.1 * viewportHeight
        gradient: Gradient {
            orientation: Gradient.Vertical
            GradientStop { position: 0.0; color: "transparent" }
            GradientStop { position: 0.5; color: "black" }
        }
    }
    Rectangle {
        anchors.top: bottomFade.bottom
        anchors.bottom: parent.bottom
        anchors.left: parent.left
        width: parent.width
        color: "black"
    }
}

現(xiàn)在，我們已經(jīng)定義了一些應(yīng)用程序的QML類型，我們將它們排列在主QML文件上。

main.qml

import "QuickMirrorTypes"

Window {
    visible: true
    title: qsTr("Quick Mirror")
    Flickable {
        anchors.fill: parent
        contentWidth: mirror.width
        contentHeight: mirror.height
        Rectangle {
            id: mirror
            width: 1080
            height: 1920
            color: "black"

            Clock {
                id: clock
                anchors.top: mirror.top
                anchors.left: mirror.left
            }

            Calendar {
                id: calendar
                anchors.top: clock.bottom
                anchors.topMargin: -20
                anchors.left: mirror.left
            }

            Rectangle {
                anchors.top: calendar.bottom
                anchors.topMargin: -5
                anchors.left: mirror.left
                width: 800
                height: 2
                color: "white"
            }

            OnThisDay {
                id: onThisDay
                anchors.top: calendar.bottom
                anchors.left: mirror.left
                anchors.leftMargin: 10
                anchors.bottom: mirror.bottom
                width: 780
                viewportHeight: 260
            }
        }
    }
}

最后，qmldir 必須將QML文件和該文件全部添加到應(yīng)用程序的資源文件中：

• 雙擊項(xiàng)目樹中的QRC文件
• 在“ Qt資源編輯器”窗口中，按“添加>添加文件”
• 選擇所有QML文件和qmldir文件
• 在Qt資源編輯器中按“保存”

構(gòu)建和部署后，我們將能夠啟動應(yīng)用程序并查看顯示的信息。

樹莓派顯示器

在Raspberry Pi上運(yùn)行的應(yīng)用程序

在Visual Studio中進(jìn)行調(diào)試

VS支持通過調(diào)試在WSL上運(yùn)行的應(yīng)用程序gdb。要在Raspberry Pi上運(yùn)行時進(jìn)行調(diào)試，我們將使用啟動應(yīng)用程序gdbserver，然后配置gdb為連接到設(shè)備并啟動遠(yuǎn)程調(diào)試會話。

為此，gdb WSL中安裝的組件必須支持目標(biāo)設(shè)備體系結(jié)構(gòu)。一種簡單的方法是安裝gdb-multiarch。為了確保VS使用正確的調(diào)試器，我們將創(chuàng)建從gdb到的符號鏈接gdb-multiarch。

WSL命令外殼

user@buildhost:~$ sudo apt-get install gdb-multiarch
...
user@buildhost:~$ cd /usr/bin
user@buildhost:/usr/bin$ sudo mv gdb gdb-bkup
user@buildhost:/usr/bin$ sudo ln -s gdb-multiarch gdb
user@buildhost:/usr/bin$ ls -go gdb*
lrwxrwxrwx 1 13 Sep 2 11:31 gdb -> gdb-multiarch
-rwxr-xr-x 1 8440200 Feb 11 2020 gdb-bkup
-rwxr-xr-x 1 15192808 Feb 11 2020 gdb-multiarch
user@buildhost:/usr/bin$

要在Visual Studio中設(shè)置遠(yuǎn)程調(diào)試會話，必須將兩個附加命令傳遞給gdb。這是在“ GDB調(diào)試器”屬性頁面中配置的。

Project Properties > Debugging > Additional Debugger Commands

target extended-remote 192.168.1.98:2345
set remote exec-file /home/pi/QuickMirror.out

在開始遠(yuǎn)程調(diào)試會話之前，我們必須設(shè)置所需的環(huán)境變量并gdbserver在設(shè)備上啟動。

Raspberry Pi命令外殼

pi@raspberry-pi:~$ export LD_LIBRARY_PATH="/usr/local/qt5pi/lib"
pi@raspberry-pi:~$ export QT_QPA_PLATFORM="eglfs"
pi@raspberry-pi:~$ export QT_QPA_PLATFORM_PLUGIN_PATH="/usr/local/qt5pi/plugins/platforms"
pi@raspberry-pi:~$ export QT_QPA_EGLFS_PHYSICAL_WIDTH="326"
pi@raspberry-pi:~$ export QT_QPA_EGLFS_PHYSICAL_HEIGHT="520"
pi@raspberry-pi:~$ export QML2_IMPORT_PATH="/usr/local/qt5pi/qml"
pi@raspberry-pi:~$ gdbserver --once --multi :2345
Listening on port 2345

按F5將啟動遠(yuǎn)程調(diào)試會話。

在遠(yuǎn)程調(diào)試期間在C ++代碼中的斷點(diǎn)處停止

遠(yuǎn)程QML調(diào)試

在嵌入式設(shè)備上運(yùn)行應(yīng)用程序時，也可以調(diào)試QML代碼。

• 在Qt設(shè)置中啟用QML調(diào)試：項(xiàng)目屬性> Qt項(xiàng)目設(shè)置
  
  
• 用于啟動QML調(diào)試會話的安裝程序參數(shù)

項(xiàng)目屬性>調(diào)試>程序參數(shù)

-qmljsdebugger=port:8989,host:192.168.1.98,block

打包

我們已經(jīng)展示了如何使用Qt VS Tools擴(kuò)展在帶有Qt Quick的Visual Studio中創(chuàng)建多平臺嵌入式應(yīng)用程序。這包括：

• 從頭開始創(chuàng)建Qt Quick項(xiàng)目
• 用QML編寫應(yīng)用程序代碼
• 交叉編譯應(yīng)用程序
• 在嵌入式設(shè)備上部署和運(yùn)行
• 在Visual Studio中對C ++和QML代碼進(jìn)行遠(yuǎn)程調(diào)試

該項(xiàng)目，包括所有源代碼，可從以下網(wǎng)址獲得：https : //github.com/micosta/quickmirror。

應(yīng)用程序在嵌入式設(shè)備上運(yùn)行

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