一、Qt?Widgets 問題交流

1.

二、Qt Quick?問題交流

1.QML單例動態創建的對象，訪問外部id提示undefined

先定義一個窗口組件，打印外部的id：

// MyWindow.qml
import QtQuick 2.15
import QtQuick.Window 2.15Window {id: controlwidth: 400height: 300visible: falseMouseArea {anchors.fill: parentonClicked: {// transientParent設置parent后可以正常訪問console.log(control.transientParent)// 單例創建的不能訪問外部的idconsole.log(root)}}
}

單例動態創建MyWindow :

// MySingleton.qml
pragma Singleton
import QtQuick 2.15Item {function createWindow(parent = null){let comp = Qt.createComponent("MyWindow.qml", Component.PreferSynchronous, parent)let win = comp.createObject(parent)return win}
}

測試可以看到在非單例動態創建的對象可以訪問外部id，動態創建的不行：

import QtQuick 2.15
import QtQuick.Window 2.15
import QtQuick.Controls 2.15Window {id: rootwidth: 640height: 480visible: truetitle: qsTr("GongJianBo")Row {anchors.fill: parentspacing: 10Button {text: "Singleton"onClicked: {let win = MySingleton.createWindow(root)win.show()}}Button {text: "Normal"onClicked: {let comp = Qt.createComponent("MyWindow.qml")let win = comp.createObject(root)win.show()}}}
}

將Window類型替換成Rectangle也是一樣的結果。

三、其他

1.Qt5 QImage?SmoothTransformation 縮放后格式改變

Qt Bug Tracker：https://bugreports.qt.io/browse/QTBUG-49719

測試代碼：

    QImage img = QImage(100, 100, QImage::Format_RGB888);img.fill(Qt::red);qDebug() << img.format();// 輸出：QImage::Format_RGB888img = img.scaled(50, 50, Qt::KeepAspectRatio, Qt::SmoothTransformation);qDebug() << img.format();// Qt5輸出：QImage::Format_RGB32// Qt6輸出：QImage::Format_RGB888

如RGB888變成了RGB32，ARGB32變成了ARGB32_Premultiplied等

從源碼一探究竟，scaled函數中調用了transformed函數：?

QImage QImage::scaled(const QSize& s, Qt::AspectRatioMode aspectMode, Qt::TransformationMode mode) const
{if (!d) {qWarning("QImage::scaled: Image is a null image");return QImage();}if (s.isEmpty())return QImage();QSize newSize = size();newSize.scale(s, aspectMode);newSize.rwidth() = qMax(newSize.width(), 1);newSize.rheight() = qMax(newSize.height(), 1);if (newSize == size())return *this;Q_TRACE_SCOPE(QImage_scaled, s, aspectMode, mode);QTransform wm = QTransform::fromScale((qreal)newSize.width() / width(), (qreal)newSize.height() / height());QImage img = transformed(wm, mode);return img;
}

transformed函數中調用了smoothScaled函數：

QImage QImage::transformed(const QTransform &matrix, Qt::TransformationMode mode ) const
{... ...// Make use of the optimized algorithm when we're scalingif (scale_xform && mode == Qt::SmoothTransformation) {if (mat.m11() < 0.0F && mat.m22() < 0.0F) { // horizontal/vertical flipreturn smoothScaled(wd, hd).mirrored(true, true);} else if (mat.m11() < 0.0F) { // horizontal flipreturn smoothScaled(wd, hd).mirrored(true, false);} else if (mat.m22() < 0.0F) { // vertical flipreturn smoothScaled(wd, hd).mirrored(false, true);} else { // no flippingreturn smoothScaled(wd, hd);}}... ...
}

smoothScaled中就需要轉換成固定的幾種格式來縮放了：

QImage QImage::smoothScaled(int w, int h) const {QImage src = *this;switch (src.format()) {case QImage::Format_RGB32:case QImage::Format_ARGB32_Premultiplied:
#if Q_BYTE_ORDER == Q_LITTLE_ENDIANcase QImage::Format_RGBX8888:
#endifcase QImage::Format_RGBA8888_Premultiplied:
#if QT_CONFIG(raster_64bit)case QImage::Format_RGBX64:case QImage::Format_RGBA64_Premultiplied:break;case QImage::Format_RGBA64:src = src.convertToFormat(QImage::Format_RGBA64_Premultiplied);break;
#endifdefault:if (src.hasAlphaChannel())src = src.convertToFormat(QImage::Format_ARGB32_Premultiplied);elsesrc = src.convertToFormat(QImage::Format_RGB32);}src = qSmoothScaleImage(src, w, h);if (!src.isNull())copyMetadata(src.d, d);return src;
}QImage qSmoothScaleImage(const QImage &src, int dw, int dh)
{QImage buffer;if (src.isNull() || dw <= 0 || dh <= 0)return buffer;int w = src.width();int h = src.height();QImageScaleInfo *scaleinfo =qimageCalcScaleInfo(src, w, h, dw, dh, true);if (!scaleinfo)return buffer;buffer = QImage(dw, dh, src.format());if (buffer.isNull()) {qWarning("QImage: out of memory, returning null");qimageFreeScaleInfo(scaleinfo);return QImage();}#if QT_CONFIG(raster_64bit)if (src.depth() > 32)qt_qimageScaleRgba64(scaleinfo, (QRgba64 *)buffer.scanLine(0),dw, dh, dw, src.bytesPerLine() / 8);else
#endifif (src.hasAlphaChannel())qt_qimageScaleAARGBA(scaleinfo, (unsigned int *)buffer.scanLine(0),dw, dh, dw, src.bytesPerLine() / 4);elseqt_qimageScaleAARGB(scaleinfo, (unsigned int *)buffer.scanLine(0),dw, dh, dw, src.bytesPerLine() / 4);qimageFreeScaleInfo(scaleinfo);return buffer;
}

查看Qt6的代碼，發現調用smoothScaled后又轉換回原格式了：

QImage Q_TRACE_INSTRUMENT(qtgui) QImage::transformed(const QTransform &matrix, Qt::TransformationMode mode ) const
{... ...if (scale_xform && mode == Qt::SmoothTransformation) {switch (format()) {case QImage::Format_RGB32:case QImage::Format_ARGB32_Premultiplied:
#if Q_BYTE_ORDER == Q_LITTLE_ENDIANcase QImage::Format_RGBX8888:
#endifcase QImage::Format_RGBA8888_Premultiplied:
#if QT_CONFIG(raster_64bit)case QImage::Format_RGBX64:case QImage::Format_RGBA64_Premultiplied:
#endifcase QImage::Format_CMYK8888:// Use smoothScaled for scaling when we can do so without conversion.if (mat.m11() > 0.0F && mat.m22() > 0.0F)return smoothScaled(wd, hd);break;default:break;}// Otherwise only use it when the scaling factor demands it, or the image is large enough to scale multi-threadedif (nonpaintable_scale_xform
#if QT_CONFIG(thread) && !defined(Q_OS_WASM)|| (ws * hs) >= (1<<20)
#endif) {QImage scaledImage;if (mat.m11() < 0.0F && mat.m22() < 0.0F) { // horizontal/vertical flipscaledImage = smoothScaled(wd, hd).mirrored(true, true);} else if (mat.m11() < 0.0F) { // horizontal flipscaledImage = smoothScaled(wd, hd).mirrored(true, false);} else if (mat.m22() < 0.0F) { // vertical flipscaledImage = smoothScaled(wd, hd).mirrored(false, true);} else { // no flippingscaledImage = smoothScaled(wd, hd);}switch (format()) {case QImage::Format_Mono:case QImage::Format_MonoLSB:case QImage::Format_Indexed8:return scaledImage;default:return scaledImage.convertToFormat(format());}}}... ...
}

2.Qt Creator 15/16 等新版本工具菜單沒有翻譯相關選項

Qt Creator 15/16 等新版本的工具菜單中，外部選項里沒有翻譯相關選項了，但是可以手動添加回去，參考：https://blog.csdn.net/weixin_53735713/article/details/144442073

在外部配置選項里選擇添加工具：

// 新增工具-更新翻譯lupdate
%{CurrentDocument:Project:QT_INSTALL_BINS}\lupdate
%{CurrentDocument:Project:FilePath}
%{CurrentDocument:Project:Path}// 新增工具-發布翻譯lrelease
%{CurrentDocument:Project:QT_INSTALL_BINS}\lrelease
%{CurrentDocument:Project:FilePath}
%{CurrentDocument:Project:Path}

三行分別對應：執行檔，參數，工作目錄，在測試時參數前面多加了個空格導致執行參數有問題。

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