SWT源码分析 (六)
第一篇文章中，有一个问题我没有解释，在Display中的runDeferedEvents方法中：boolean runDeferredEvents () {boolean run = false;/** Run deferred events.This code is always* called in the Display's thread so it must* be re-enterant but need not be synchronized.*/while (eventQueue != null) {/* Take an event off the queue */Event event = eventQueue ;if (event == null) break;int length = eventQueue.length;System.arraycopy (eventQueue, 1, eventQueue, 0, --length);eventQueue = null;/* Run the event */Widget widget = event.widget;if (widget != null && !widget.isDisposed ()) {Widget item = event.item;if (item == null || !item.isDisposed ()) {run = true;widget.sendEvent (event);}}/** At this point, the event queue could* be null due to a recursive invocation* when running the event.*/}/* Clear the queue */eventQueue = null;return run;} 事件event是从eventQueue中取出来的，eventQueue是Display中的一个Event数组：
Event [] eventQueue; 我自然就会想到，系统中的各种事件，是怎么放入这个eventQueue中的呢？
继续从上文的按钮程序入手，现在监听按钮1的鼠标按下事件：
package com.edgar;import org.eclipse.swt.SWT;import org.eclipse.swt.events.MouseAdapter;import org.eclipse.swt.events.MouseEvent;import org.eclipse.swt.widgets.Button;import org.eclipse.swt.widgets.Display;import org.eclipse.swt.widgets.Shell;class TestMultButton { public static void main(String[] args) { Display display = new Display();// 创建一个display对象。 final Shell shell = new Shell(display);// shell是程序的主窗体 shell.setText("Java应用程序"); // 设置主窗体的标题 shell.setSize(300, 300); // 设置主窗体的大小 Button b1 = new Button(shell,SWT.NONE); b1.setText("按钮1"); b1.setBounds(100,50, 100, 50); Button b2 = new Button(shell,SWT.NONE); b2.setText("按钮2"); b2.setBounds(100,150, 100, 50); b1.addMouseListener(new MouseAdapter() {@Overridepublic void mouseDown(MouseEvent e) {// TODO Auto-generated method stubSystem.out.println("mousedown");}}); shell.open(); // 打开主窗体 while (!shell.isDisposed()) { // 如果主窗体没有关闭则一直循环 if (!display.readAndDispatch()) { // 如果display不忙 display.sleep(); // 休眠 } } display.dispose(); // 销毁display }} 我在System.out.println("mousedown");这行代码加上断点，然后运行程序，然后点击按钮一，程序暂停，运行上下文如下：
http://dl.iteye.com/upload/attachment/424716/c5c8e2c0-899e-3df9-85c5-c7f8ad0f2157.png
程序执行的流程和分析一中的一样，我们并没有看到上下文中看到windowProc，这是“意料之中”的，因为我们在利用SWT这个GUI类库编程，几乎搜有GUI类库都会对消息循环，窗口过程函数进行封装，让我们能以OO的方式来编程。现在为了知道SWT是怎么进行封装的，我找到Control类中的 windowProc 方法：
int /*long*/ windowProc (int /*long*/ hwnd, int msg, int /*long*/ wParam, int /*long*/ lParam) {LRESULT result = null;switch (msg) {......case OS.WM_KILLFOCUS:result = WM_KILLFOCUS (wParam, lParam); break;case OS.WM_LBUTTONDBLCLK:result = WM_LBUTTONDBLCLK (wParam, lParam); break;case OS.WM_LBUTTONDOWN:result = WM_LBUTTONDOWN (wParam, lParam); break;case OS.WM_LBUTTONUP:result = WM_LBUTTONUP (wParam, lParam); break;......}if (result != null) return result.value;return callWindowProc (hwnd, msg, wParam, lParam);} 对应左键点击按钮来说，windowProc中会接收到WM_LBUTTONDOWN消息，然后会调用WM_LBUTTONDOWN(wParam,lParam)函数，所以我在WM_LBUTTONDOWN函数加一个断点：
http://dl.iteye.com/upload/attachment/424722/2d766406-6898-36f7-ad5b-bfafe111c30a.png
运行程序，点击按钮一后，程序果然停在return wmLButtonDown (handle, wParam, lParam);这行！
现在我们就进入wmLButtonDown(handle,wParam,lParam)方法里面，看看都有什么操作:
LRESULT wmLButtonDown (int /*long*/ hwnd, int /*long*/ wParam, int /*long*/ lParam) {Display display = this.display;LRESULT result = null;int x = OS.GET_X_LPARAM (lParam);int y = OS.GET_Y_LPARAM (lParam);boolean [] consume = null, detect = null;boolean dragging = false, mouseDown = true;int count = display.getClickCount (SWT.MouseDown, 1, hwnd, lParam);if (count == 1 && (state & DRAG_DETECT) != 0 && hooks (SWT.DragDetect)) {if (!OS.IsWinCE) {/** Feature in Windows.It's possible that the drag* operation will not be started while the mouse is* down, meaning that the mouse should be captured.* This can happen when the user types the ESC key* to cancel the drag.The fix is to query the state* of the mouse and capture the mouse accordingly.*/detect = new boolean ;consume = new boolean ;dragging = dragDetect (hwnd, x, y, true, detect, consume);if (isDisposed ()) return LRESULT.ZERO;mouseDown = OS.GetKeyState (OS.VK_LBUTTON) < 0;}}display.captureChanged = false;boolean dispatch = sendMouseEvent (SWT.MouseDown, 1, count, 0, false, hwnd, OS.WM_LBUTTONDOWN, wParam, lParam);if (dispatch && (consume == null || !consume )) {result = new LRESULT (callWindowProc (hwnd, OS.WM_LBUTTONDOWN, wParam, lParam));} else {result = LRESULT.ZERO;}if (OS.IsPPC) {/** Note: On WinCE PPC, only attempt to recognize the gesture for* a context menu when the control contains a valid menu or there* are listeners for the MenuDetect event.*/Menu menu = getMenu ();boolean hasMenu = menu != null && !menu.isDisposed ();if (hasMenu || hooks (SWT.MenuDetect)) {SHRGINFO shrg = new SHRGINFO ();shrg.cbSize = SHRGINFO.sizeof;shrg.hwndClient = hwnd;shrg.ptDown_x = x;shrg.ptDown_y = y; shrg.dwFlags = OS.SHRG_RETURNCMD;int type = OS.SHRecognizeGesture (shrg);if (type == OS.GN_CONTEXTMENU) showMenu (x, y);}}if (mouseDown) {if (!display.captureChanged && !isDisposed ()) {if (OS.GetCapture () != hwnd) OS.SetCapture (hwnd);}}if (dragging) {sendDragEvent (1, x, y);} else {if (detect != null && detect ) {/** Feature in Windows.DragDetect() captures the mouse* and tracks its movement until the user releases the* left mouse button, presses the ESC key, or moves the* mouse outside the drag rectangle.If the user moves* the mouse outside of the drag rectangle, DragDetect()* returns true and a drag and drop operation can be* started.When the left mouse button is released or* the ESC key is pressed, these events are consumed by* DragDetect() so that application code that matches* mouse down/up pairs or looks for the ESC key will not* function properly.The fix is to send the missing* events when the drag has not started.* * NOTE: For now, don't send a fake WM_KEYDOWN/WM_KEYUP* events for the ESC key.This would require computing* wParam (the key) and lParam (the repeat count, scan code,* extended-key flag, context code, previous key-state flag,* and transition-state flag) which is non-trivial.*/if (OS.GetKeyState (OS.VK_ESCAPE) >= 0) {OS.SendMessage (hwnd, OS.WM_LBUTTONUP, wParam, lParam);}}}return result;} 方法有点长，但是真正执行的地方并不长。一开始得到点击事件的x坐标和y坐标，然后得到点击的次数，然后调用sendMouseEvent方法：
boolean dispatch = sendMouseEvent (SWT.MouseDown, 1, count, 0, false, hwnd, OS.WM_LBUTTONDOWN, wParam, lParam); 看方法的名字是“发送鼠标事件”进入该方法：
boolean sendMouseEvent (int type, int button, int count, int detail, boolean send, int /*long*/ hwnd, int msg, int /*long*/ wParam, int /*long*/ lParam) {if (!hooks (type) && !filters (type)) return true;Event event = new Event ();event.button = button;event.detail = detail;event.count = count;event.x = OS.GET_X_LPARAM (lParam);event.y = OS.GET_Y_LPARAM (lParam);setInputState (event, type);mapEvent (hwnd, event);if (send) {sendEvent (type, event);if (isDisposed ()) return false;} else {postEvent (type, event);}return event.doit;} 我们看到方法里面将系统的消息 “转换”成了SWT自己的事件对象。给event对象的属性赋值之后，因为send的值是false(看调用的代码和形参对应起来！)，所以调用postEvent(type,event)方法：
void postEvent (int eventType, Event event) {sendEvent (eventType, event, false);} 又调用了sendEvent方法：
void sendEvent (int eventType, Event event, boolean send) {if (eventTable == null && !display.filters (eventType)) {return;}if (event == null) event = new Event ();event.type = eventType;event.display = display;event.widget = this;if (event.time == 0) {event.time = display.getLastEventTime ();}if (send) {sendEvent (event);} else {display.postEvent (event);}} 给属性赋值之后，因为send是false，继续调用display.postEvent(event):
void postEvent (Event event) {/** Place the event at the end of the event queue.* This code is always called in the Display's* thread so it must be re-enterant but does not* need to be synchronized.*/if (eventQueue == null) eventQueue = new Event ;int index = 0;int length = eventQueue.length;while (index < length) {if (eventQueue == null) break;index++;}if (index == length) {Event [] newQueue = new Event ;System.arraycopy (eventQueue, 0, newQueue, 0, length);eventQueue = newQueue;}eventQueue = event;} postEvent方法，正是把此时的事件event存入了eventQueue。好了，文章一遗留的问题解决了。
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