問題描述

我必須從暴露 DLLStart 和 DLLStop 的 dll 啟動 Qt GUI.main中正常的(.exe)方式如下:

I have to start a Qt GUI from a dll exposing DLLStart and DLLStop. The normal (.exe) approach in main is as follows:

int main(int argc, char *argv[]) {
    QApplication a(argc, argv); Dialog w;
    w.show();
    return a.exec();
}

問題是阻塞 a.exec() 調(diào)用，因為在 dll 中 DLLStart 需要立即返回(見下文).有什么解決方法嗎?備注:該問題與將 Qt GUI 添加到一個動態(tài)庫 "，但它不是完全重復(fù)的.

The problem is the blocking a.exec() call, since in the dll DLLStart needs to return immediately (see below). Any workaround for this? Remark: The question is sharing some common ground with " Adding a Qt GUI to a Dynamic Library ", but it is no exact duplicate.

/** start module  */
int __stdcall DLLStart(void) {
    .. 
    QApplication qaDll(ac, av); Dialog w;
    w.show();
    qaDll.exec();
    return 0; // never reached
}

/** stop module */
void __stdcall DLLStop(void) { }

推薦答案

在 Windows 上工作的一種方法是在單獨的 QThread 中啟動 QApplication.它不可移植——它不適用于 OS X(我正在研究修復(fù)).

One way works on Windows is to start QApplication in a separate QThread. It's not portable -- it doesn't work on OS X (I'm researching a fix).

但是，您不需要單獨的線程.如果您將代碼注入到正在運行的應(yīng)用程序中，則它已經(jīng)有一個事件循環(huán).你只需要創(chuàng)建一個全局的 QApplication 對象就可以了.事件循環(huán)已在運行，因此您無需調(diào)用 exec().Qt 的窗口與本機事件循環(huán)集成，在這方面一切都很好.

But, you don't need a separate thread. If you inject your code into a running application, it already has an event loop. You only need to create a global QApplication object and you're done. The event loop is already running, so you don't need to call exec(). Qt's windows integrate with the native event loop, and everything is good on that front.

您確實需要調(diào)用一次 QCoreApplication::processEvents.它將當(dāng)前的應(yīng)用程序?qū)嵗傻?windows 事件循環(huán)中，就是這樣.

You do need to call QCoreApplication::processEvents once. It will integrate the current application instance into the windows event loop, and that's it.

因此，您的啟動代碼可能如下所示:

Thus, your startup code could look as follows:

static struct Data {
  int argc = 1;
  char *argv[2] = {strdup("dummy"), {}};
  QApplication app{argc, argv};
  MainWindow win;
} *d;

static void startup() {
  d = new Data;
  d->win.show();
  d->app.processEvents();
}

static void shutdown() {
  delete d;
}

startup() 和 shutdown() 應(yīng)該在適當(dāng)?shù)臅r間(在進(jìn)程附加和分離時)調(diào)用.

The startup() and shutdown() should be called at appropriate times (on process attach and detach).

舊答案如下.這不再是完全最新的.

Old answer follows. This is not completely up to date anymore.

下面是一個簡短的例子，一個完整的自包含例子見我的其他答案.

A short example is below, for a complete self-contained example see my other answer.

它不可移植，這就是 Qt 文檔反對它的原因.它在 Windows 上運行良好.主線程不是魔術(shù)——不是在 Windows 上.OS X 上的 Cocoa 在某種程度上很笨拙，顯然是不可能的:(.

It is not portable and that's why Qt documentation advises against it. It works just fine on Windows. The main thread is not magic -- not on Windows. Cocoa on OS X is clumsy in a way and makes it impossible, apparently :(.

請注意，如果加載 DLL 的應(yīng)用程序已經(jīng)使用 Qt，那么您無需再執(zhí)行任何操作.確保使用相同的 C++ 編譯器編譯 DLL，鏈接到相同的 C++ 運行時，并使用與應(yīng)用程序使用的二進(jìn)制兼容的 Qt 版本.這樣您就不需要自己的 QApplication 實例.要完成一些有用的工作，請顯示一個 Widget 或使用計時器實例化一些 QObjects 以使它們忙碌.您也可以使用 QMetaObject::invokeMethod(obj, "mySlot", Qt::QueuedConnection) 而不是使用計時器:當(dāng)控制返回到事件循環(huán)時將進(jìn)行調(diào)用.

Note that if the application that loads the DLL already uses Qt, then there's nothing further for you to do. Ensure you compile your DLL with the same C++ compiler, link against the same C++ runtime, and use a version of Qt that's binary compatible with the one used by application. You then don't need your own instance of QApplication. To get some useful work done, show a Widget or instantiate some QObjects with timers that will get them busy. You can also use QMetaObject::invokeMethod(obj, "mySlot", Qt::QueuedConnection) instead of using timers: the call will be made when control returns to the event loop.

如果這是不可能的，那么下面是您唯一的選擇.據(jù)我所知，效果很好.

If that's not possible, then the below is your only option. Works just fine, as far as I can tell.

請注意，我在這里有點諷刺:如果您是使用 DLL 的應(yīng)用程序的作者，則上一段中的條件將可靠地滿足.否則——忘記它.

Note that I'm a bit sarcastic here: The conditions in the previous paragraph will be met reliably maybe if you are the author of the application that uses the DLL. Otherwise -- forget about it.

class AppThread : public QThread {
  int & argc;
  char ** argv;
  int result;
  void run() {
    QApplication a(argc, argv);
    Dialog d;
    d.show();
    result = a.exec();
  }
public:
  AppThread(int & argc, char ** argv) : argc(argc), argv(argv) {}
  ~AppThread() { quit(); wait(); }
}

extern "C" int __stdcall DLLStart(void) {
  auto *thread = new AppThread(argc, argv);
  thread->start();
  return 0;
}

extern "C" void __stdcall DLLStop(void) {
  delete qApp->thread();
}

這篇關(guān)于從 dll 啟動 Qt GUI(在 DLLStart 函數(shù)中)的文章就介紹到這了，希望我們推薦的答案對大家有所幫助，也希望大家多多支持html5模板網(wǎng)！