inside SWT: start from OS
SWT程序设计中，Display充当SWT与底层操作系统、UI线程之间的桥梁，而OS类是Display实现的基础。OS对界面部分操作系统底层API进行了封装，其父类C实现了内存操作函数，从而使得java中也可以像C/C++一样设计界面。
我们知道，基本的windows程序设计一般需要注册窗口类、创建窗口、处理消息循环三个过程，通过OS我们完全可以用java代码实现以上过程，看例子：纯OS实现的hello world！
import org.eclipse.swt.SWT;import org.eclipse.swt.internal.Callback;import org.eclipse.swt.internal.win32.MSG;import org.eclipse.swt.internal.win32.OS;import org.eclipse.swt.internal.win32.PAINTSTRUCT;import org.eclipse.swt.internal.win32.RECT;import org.eclipse.swt.internal.win32.TCHAR;import org.eclipse.swt.internal.win32.WNDCLASS;public class App {public static void main(String[] args) {App app = new App();app.registerClass();app.InitInstance();app.readAndDispatchMessage();}private TCHAR windowClass;private int hInstance;private Callback windowCallback;private int windowProc;private int hwndMessage;private boolean quit;private final PAINTSTRUCT lpPaint = new PAINTSTRUCT();private final RECT rect = new RECT();private void error(int errorNoMoreCallbacks) {throw new RuntimeException("error");}private void InitInstance() {// 创建窗口hwndMessage = OS.CreateWindowEx(0, windowClass, null, OS.WS_BORDER | OS.WS_VISIBLE | OS.WS_SYSMENU, 0, 0, 0, 0, 0, 0, hInstance, null);String title = "SWT_Window";OS.SetWindowText(hwndMessage, new TCHAR(0, title, true));OS.SetWindowPos(hwndMessage, 0, 100, 100, 400, 300, 0);OS.ShowWindow(hwndMessage, OS.SW_SCROLLCHILDREN);OS.UpdateWindow(hwndMessage);}// 消息循环public void readAndDispatchMessage() {MSG msg = new MSG();while (!quit) {if (OS.PeekMessage(msg, 0, 0, 0, OS.PM_REMOVE)) {OS.TranslateMessage(msg);OS.DispatchMessage(msg);}OS.WaitMessage();}}// 注册窗口类protected void registerClass() {// 回调函数windowCallback = new Callback(this, "windowProc", 4); //$NON-NLS-1$windowProc = windowCallback.getAddress();if (windowProc == 0) {error(SWT.ERROR_NO_MORE_CALLBACKS);}// 注册窗口类windowClass = new TCHAR(0, "SWT_Window", true);int hHeap = OS.GetProcessHeap();hInstance = OS.GetModuleHandle(null);WNDCLASS lpWndClass = new WNDCLASS();lpWndClass.hInstance = hInstance;lpWndClass.lpfnWndProc = windowProc;lpWndClass.style = OS.CS_HREDRAW | OS.CS_VREDRAW | OS.CS_GLOBALCLASS;lpWndClass.hCursor = OS.LoadCursor(0, OS.IDC_ARROW);lpWndClass.hbrBackground = OS.BLACK_BRUSH;int byteCount = windowClass.length() * TCHAR.sizeof;lpWndClass.lpszClassName = OS.HeapAlloc(hHeap, OS.HEAP_ZERO_MEMORY, byteCount);OS.MoveMemory(lpWndClass.lpszClassName, windowClass, byteCount);OS.RegisterClass(lpWndClass);OS.HeapFree(hHeap, 0, lpWndClass.lpszClassName);}// 回调函数int windowProc(int hwnd, int msg, int wParam, int lParam) {String helloWorld = "hello World!";switch (msg) {case OS.WM_PAINT:int hDC = OS.BeginPaint(hwnd, lpPaint);OS.GetWindowRect(hwndMessage, rect);rect.right -= rect.left;rect.left = 0;rect.bottom -= rect.top;rect.top = 0;OS.DrawTextW(hDC, helloWorld.toCharArray(), helloWorld.length(), rect, OS.DT_CENTER);OS.EndPaint(hwnd, lpPaint);break;case OS.WM_CLOSE:quit = true;break;default:return OS.DefWindowProc(hwnd, msg, wParam, lParam);}return 0;}} 运行上面的程序生成窗口如下：
http://dl.iteye.com/upload/picture/pic/66228/81844c7b-931e-30f5-ab22-daf204f9c2c8.png
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