几年前我做了一些Win32 GUI编程.现在我正在使用Java Swing.
出于好奇,Win32消息循环逻辑的Swing对应物在哪里？在Win32中,它是通过API GetMessage()实现的.我想它肯定已被深深地包裹在某个地方.
Rad*_*def 11
下图概括地说明了Swing/AWT在Windows平台上的工作原理:
Our Listeners
?
? (Events dispatched to our code by EDT)
? ???????????????????????
? Event Dispatch Thread ?
??????????????????????? ?
? (Events pulled from the queue by EDT)
?
Event Queue
?
? (Events posted to the queue by WToolkit)
? ???????????????????????
? WToolkit Thread ?
??????????????????????? ?
? (Messages pulled by WToolkit via PeekMessage)
?
Windows API
事件驱动的抽象几乎完全隐藏了这种体系结构.我们只与最顶层的最终互动时,事件被触发(actionPerformed,paintComponent,等)和偶尔发布自己的活动(invokeLater,repaint,等).
关于这个主题的官方文档往往非常一般,所以我将使用源代码中的(非常复述)摘录.
EDT是Swing事件处理线程,所有Swing程序主要在此线程上运行.在大多数情况下,这只是AWT系统,它位于java.awt.EventDispatchThread.
事件调度系统非常分散,所以我将通过一个特定的例子来假设JButton已经点击了.
为了开始弄清楚发生了什么,我们可能会看一下堆栈跟踪.
class ClickStack {
public static void main(String[] args) {
SwingUtilities.invokeLater(new Runnable() {
@Override
public void run() {
JFrame frame = new JFrame();
JButton button = new JButton("Click for stack trace");
button.addActionListener(new ActionListener() {
@Override
public void actionPerformed(ActionEvent ae) {
new Error().printStackTrace(System.out);
}
});
frame.add(button);
frame.pack();
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setVisible(true);
}
});
}
}
该程序为我们提供了如下调用堆栈:
at sscce.ClickStack$1$1.actionPerformed
at javax.swing.AbstractButton.fireActionPerformed
...
at javax.swing.DefaultButtonModel.setPressed
at javax.swing.plaf.basic.BasicButtonListener.mouseReleased
at java.awt.Component.processMouseEvent
...
at java.awt.Component.processEvent
...
at java.awt.Component.dispatchEventImpl
...
at java.awt.Component.dispatchEvent
at java.awt.EventQueue.dispatchEventImpl
...
at java.awt.EventQueue.dispatchEvent
at java.awt.EventDispatchThread.pumpOneEventForFilters
at java.awt.EventDispatchThread.pumpEventsForFilter
...
at java.awt.EventDispatchThread.pumpEvents
at java.awt.EventDispatchThread.run
如果我们看看这个EventDispatchThread.run方法,我们会看到:
public void run() {
try {
pumpEvents(...);
} finally {
...
}
}
EventDispatchThread.pumpEvents将我们带到EventDispatchThread.pumpEventsForFilter包含外部循环逻辑的内容:
void pumpEventsForFilter(...) {
...
while(doDispatch && ...) {
pumpOneEventForFilters(...);
}
...
}
然后将一个事件从队列中拉出并发送给以下发送EventDispatchThread.pumpOneEventForFilters:
void pumpOneEventForFilters(...) {
AWTEvent event = null;
...
try {
...
EventQueue eq = getEventQueue();
...
event = eq.getNextEvent();
...
eq.dispatchEvent(event);
...
} catch(...) {
...
} ...
}
java.awt.EventQueue包含缩小事件类型并进一步调度事件的逻辑.EventQueue.dispatchEvent调用EventQueue.dispatchEventImpl我们看到以下决策结构:
if (event instanceof ActiveEvent) {
...
((ActiveEvent)event).dispatch();
} else if (src instanceof Component) {
((Component)src).dispatchEvent(event);
...
} else if (src instanceof MenuComponent) {
((MenuComponent)src).dispatchEvent(event);
} else if (src instanceof TrayIcon) {
((TrayIcon)src).dispatchEvent(event);
} else if (src instanceof AWTAutoShutdown) {
...
dispatchThread.stopDispatching();
} else {
...
}
我们熟悉的大多数事件都经历了这Component条路.
Component.dispatchEvent调用Component.dispatchEventImpl它,对大多数听众类型的事件,称Component.processEvent该事件被缩小,再进行转发:
/**
* Processes events occurring on this component. By default this
* method calls the appropriate process<event type>Event
* method for the given class of event.
* ...
*/
protected void processEvent(AWTEvent e) {
if (e instanceof FocusEvent) {
processFocusEvent((FocusEvent)e);
} else if (e instanceof MouseEvent) {
switch(e.getID()) {
case MouseEvent.MOUSE_PRESSED:
case MouseEvent.MOUSE_RELEASED:
case MouseEvent.MOUSE_CLICKED:
case MouseEvent.MOUSE_ENTERED:
case MouseEvent.MOUSE_EXITED:
processMouseEvent((MouseEvent)e);
break;
case ...:
...
}
} else if (e instanceof KeyEvent) {
processKeyEvent((KeyEvent)e);
} else if (e instanceof ComponentEvent) {
processComponentEvent((ComponentEvent)e);
} else if (...) {
...
} ...
}
对于JButton点击,我们跟随MouseEvent.
这些低级事件最终在内部有一个处理程序Component.例如,我们可能会看看javax.swing.plaf.BasicButtonListener哪些实现了许多侦听器接口.
BasicButtonListener使用鼠标事件来更改按钮模型的按下状态.最后,按钮模型确定它是否被点击DefaultButtonModel.setPressed,触发ActionEvent并且我们的监听器actionPerformed被调用.
如何实现实际的本机窗口当然是特定于平台的,但我可以稍微浏览一下Windows平台,因为它就是你所问的内容.您将在以下目录中找到Windows平台的内容:
Windows实现java.awt.Toolkit,它为sun.awt.windows.WToolkit实际的消息循环启动一个单独的线程.WToolkit.run调用JNI方法eventLoop.源文件中的注释解释了:
/*
* eventLoop() begins the native message pump which retrieves and processes
* native events.
* ...
这导致我们进入C++ AwtToolkit类,位于awt_Toolkit.h和awt_Toolkit.cpp(其他类遵循相同的文件名约定).
调用的本机实现eventLoopAwtToolkit::MessageLoop:
AwtToolkit::GetInstance().MessageLoop(AwtToolkit::PrimaryIdleFunc,
AwtToolkit::CommonPeekMessageFunc);
(AwtToolkit::CommonPeekMessageFunc调用PeekMessage,这是非阻塞的另一个自我GetMessage.)
这是外环所在的位置:
UINT
AwtToolkit::MessageLoop(IDLEPROC lpIdleFunc,
PEEKMESSAGEPROC lpPeekMessageFunc)
{
...
m_messageLoopResult = 0;
while (!m_breakMessageLoop) {
(*lpIdleFunc)();
PumpWaitingMessages(lpPeekMessageFunc); /* pumps waiting messages */
...
}
...
}
AwtToolkit::PumpWaitingMessages实际上有一个熟悉的消息循环,调用TranslateMessage和DispatchMessage:
/*
* Called by the message loop to pump the message queue when there are
* messages waiting. Can also be called anywhere to pump messages.
*/
BOOL AwtToolkit::PumpWaitingMessages(PEEKMESSAGEPROC lpPeekMessageFunc)
{
MSG msg;
BOOL foundOne = FALSE;
...
while (!m_breakMessageLoop && (*lpPeekMessageFunc)(msg)) {
foundOne = TRUE;
ProcessMsg(msg); // calls TranslateMessage & DispatchMessage (below)
}
return foundOne;
}
void AwtToolkit::ProcessMsg(MSG& msg)
{
if (msg.message == WM_QUIT) {
...
}
else if (msg.message != WM_NULL) {
...
::TranslateMessage(&msg);
::DispatchMessage(&msg);
}
}
(并回想起那个DispatchMessage叫WindowProc回调的人.)
本机窗口由C++对象包装,该对象具有特定于平台的内容,以及Java代码中的一些API的松散并行.
似乎有几个WindowProc功能.一个只是由工具包内部使用AwtToolkit::WndProc,以及一个空窗口.
WindowProc我们真正感兴趣的功能是AwtComponent::WndProc.WndProc调用一个名为的虚函数AwtComponent::WindowProc.一些子类覆盖WindowProc(例如AwtFrame::WindowProc),但大多数消息由处理AwtComponent::WindowProc.例如,它包含以下开关案例:
case WM_LBUTTONDOWN:
case WM_LBUTTONDBLCLK:
mr = WmMouseDown(static_cast<UINT>(wParam), myPos.x, myPos.y,
LEFT_BUTTON);
break;
AwtComponent::WmMouseDown开始了一系列的职位调用java.awt.MouseEvent到EventQueueJava中:
SendMouseEvent(java_awt_event_MouseEvent_MOUSE_PRESSED, now, x, y,
GetJavaModifiers(), clickCount, JNI_FALSE,
GetButton(button), &msg);
活动结束后,我们最终被带回到EDT上可以看到活动的顶端.