如果在Ubuntu QML應用中在應用一啟動時就得到螢幕的解析度，ubuntuqml

如果在Ubuntu QML應用中在應用一啟動時就得到螢幕的解析度，ubuntuqml

對於有些應用來說，擷取螢幕解析度這個資訊可能是重要的。比如有些遊戲或閱讀器應用，希望在應用啟動後，馬上得到螢幕的解析度，這樣可以和容易地適配不同螢幕尺寸的手機或裝置。有些應用可以是用QtQuick.Window的Screen來得到這個資訊，但是我們可以看一下在文章中如下的提醒：

Note that the Screen type is not valid at Component.onCompleted, because the Item or Window has not been displayed on a screen by this time.

這也就是說我們不能使用上述的方法來得到螢幕的尺寸。通過我的實驗。顯示的結果為“0”。

為了能夠在應用啟動時得到螢幕的解析度，我們可以使用C++的代碼來實現。

screen.h

#ifndef SCREEN_H#define SCREEN_H#include <QObject>#include <QGuiApplication>#include <QScreen>#include <QDebug>class Screen : public QObject{    Q_OBJECTpublic:    Q_PROPERTY(int height READ height)    Q_PROPERTY(int width READ width)    explicit Screen(QObject *parent = 0);     int height() { return m_height; };    int width() { return m_width; };private:    int m_height;    int m_width;};#endif // FILEIO_H

screen.cpp

#include "screen.h"Screen::Screen(QObject *parent) : QObject(parent){QScreen* screen = QGuiApplication::primaryScreen();QSize screenSize =  screen->size();qDebug() << "width: " << screenSize.width();m_width = screenSize.width();m_height = screenSize.height();}

我們可以使用Ubuntu SDK提供的“QML App with C++ plugin (cmake)”來建立一個應用來測試。測試應用的代碼如下：

import QtQuick 2.0import Ubuntu.Components 1.1import Screen 1.0import QtQuick.Window 2.0/*!    \brief MainView with Tabs element.           First Tab has a single Label and           second Tab has a single ToolbarAction.*/MainView {    // objectName for functional testing purposes (autopilot-qt5)    objectName: "mainView"    // Note! applicationName needs to match the "name" field of the click manifest    applicationName: "screen.liu-xiao-guo"    /*     This property enables the application to change orientation     when the device is rotated. The default is false.    */    //automaticOrientation: true    // Removes the old toolbar and enables new features of the new header.    useDeprecatedToolbar: false    width: units.gu(50)    height: units.gu(76)    MyScreen {        id: screen    }    Page {        title: i18n.tr("App with backend")        MyType {            id: myType            Component.onCompleted: {                myType.helloWorld = i18n.tr("Hello world..")            }        }        Column {            spacing: units.gu(1)            anchors {                margins: units.gu(2)                fill: parent            }            Label {                id: label                objectName: "label"                text: myType.helloWorld            }            Button {                objectName: "button"                width: parent.width                text: i18n.tr("Tap me!")                onClicked: {                    myType.helloWorld = i18n.tr("..from Cpp Backend")                }            }        }        Component.onCompleted: {            console.log("screen width: " + screen.width);            console.log("screen height: " + screen.height);            console.log("SCREEN width: " + Screen.width );            console.log("SCREEN height: " + Screen.height)        }    }}

我們應用的輸出為：

qml: screen width: 768qml: screen height: 1280qml: SCREEN width: 0qml: SCREEN height: 0

我們可以看出來，MyScreen得到了正確的解析度，但是“Screen.width”及“Screen.height”得到的是“０”。

整個項目的源碼在：git clone https://gitcafe.com/ubuntu/screen.git