c++ - 将 QtConcurrent 用于 QImage::fill 时 Unresolved 重载函数类型

Question

我正在尝试调用QImage::fill()异步使用 QtConcurrent模块。 invert pixels example工作正常，但填充方法的类似语法不能:

#include <QApplication>
#include <QImage>
#include <QFuture>
#include <QtConcurrent/QtConcurrentRun>

int main(int argc, char *argv[])
{
  QApplication app(argc, argv);
  QImage image(1920, 1080, QImage::Format_ARGB32_Premultiplied);
  QFuture<void> future = QtConcurrent::run(&image, &QImage::fill, Qt::transparent); // ko
  //QFuture<void> future = QtConcurrent::run(&image, &QImage::invertPixels, QImage::InvertRgba); // ok
  future.waitForFinished();
  return app.exec();
}

编译失败并出现以下错误:

error: no matching function for call to ‘run(QImage*, <unresolved overloaded function type>, Qt::GlobalColor)’
   10 |   QFuture<void> future = QtConcurrent::run(&img, &QImage::fill, Qt::transparent); // ko
      |                                                                                ^
In file included from /usr/include/x86_64-linux-gnu/qt5/QtConcurrent/QtConcurrentRun:1,
                 from /home/romain/code/qt/main.cc:4:
/usr/include/x86_64-linux-gnu/qt5/QtConcurrent/qtconcurrentrun.h:72:12: note: candidate: ‘template<class T> QFuture<T> QtConcurrent::run(T (*)())’
   72 | QFuture<T> run(T (*functionPointer)())
      |            ^~~
/usr/include/x86_64-linux-gnu/qt5/QtConcurrent/qtconcurrentrun.h:72:12: note:   template argument deduction/substitution failed:
/home/romain/code/qt/main.cc:10:80: note:   mismatched types ‘T()’ and ‘QImage’
   10 |   QFuture<void> future = QtConcurrent::run(&img, &QImage::fill, Qt::transparent); // ko
      |                                                                                ^

是否可以通过显式标记某些模板类型来帮助编译器？

Answer 1

问题是 QImage::fill有多个重载。您需要使用 static_cast 来消除歧义。 ...

QFuture<void> future = QtConcurrent::run(&image, static_cast<void(QImage::*)(Qt::GlobalColor)>(&QImage::fill), Qt::transparent);

或(因为这是 Qt ) QOverload ...

QFuture<void> future = QtConcurrent::run(&image, qOverload<Qt::GlobalColor>(&QImage::fill), Qt::transparent);