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<P><B><FONT SIZE=+2>A basic example</FONT></B>
<PRE>


#include &ltX11/Xlib.h&gt
#define HELLO "hello world"

main(int argc, char **argv)
{

	Display *display;  // X server connection
	Window *win;       //  Window ID

	GC  gc;                // Grpahics context
	int bw = 2 		// Border width
	int bc = BlackPixel;  // Border color
	int bgc = WhitePixel;  // Window background color
	XSizeHints   hints;     // Window sizing hints
	XEvent  event;            // Event data Structure

	// Open the display
	display = XOpenDisplay(NULL);

	// Set hints for window size and position
	hints.x = 200; hints.y = 200;
	hints.width=300; hints.height=200;
	hints.flags= PPosition| PSize;

	// Create the window
	win = XCreateSimpleWindow(display, DefaultRootWindow(display), hints.x, hints.y,  hints.width, hints.heigth, bw, bc, bgc);

	XSetStandardProperties(display, win, HELLO, HELLO, argv, argc, &hints);

	// Create a grpahics context for writing the text
	gc = XCreateGC(dispaly, win, NULL, NULL);

	// Specify events of interest (only exposure)
	XSelectInput(display, win, ExposureMask);

	// Show the window
	XMapWindow(display, win);  

	// Event loop
	while (TRUE) {
	   XNextEvent(display, &event);
	   // Discard all but the most recent expose event
	   if (event.type == Expose && event.xexpose.count == 0){
               int x, y;
               while (XCheckTypedEvent(display, Expose, &Event));
               XClearWindow(display, win);
               //********  Print "hello world" !! ******
               XDrawImageString(display, win, gc, 50, 50, HELLO, strlen(HELLO));
       }  //End if
    }  // end while

    exit(0);

}

</PRE>
<P><B><FONT SIZE=+2>A Motif example</FONT></B>
<PRE>
<CENTER><P><IMG SRC="push.gif"><P>
图2：一个Motif编程的例子</CENTER>
<P>
#include &lt;Xm/Xm.h&gt; 
#include &lt;Xm/PushB.h&gt;

main(int argc, char **argv) 

{   Widget top_wid, button;
    XtAppContext  app;
   
    top_wid = XtVaAppInitialize(&amp;app, &quot;Push&quot;, NULL, 0,
        &amp;argc, argv, NULL, NULL);

    button = XmCreatePushButton(top_wid, &quot;Push_me&quot;, NULL, 0);

<P>  

    /* tell Xt to manage button */
	XtManageChild(button);
   
				/* attach fn to widget */
    XtAddCallback(button, XmNactivateCallback, pushed_fn, NULL);

    XtRealizeWidget(top_wid); /* display widget hierarchy */
    XtAppMainLoop(app); /* enter processing loop */ 

}

void pushed_fn(Widget w, XtPointer client_data, 
               XmPushButtonCallbackStruct *cbs) 
  {   
     printf(&quot;Don't Push Me!!\n&quot;);
  }
</PRE>
</SMALL>

Event dispatching can be handled in one of three ways.



<ul>

<li> Polling: Widgets or application programs poll the devices
for input.

<li> Messages: Events are asynchronously sent by devices to
widgets.

<li> A widget may register all callback, which is a pointer to a
function or method  that handles the event type. The window
manager will call the specified function whenever the event
occurs.

</ul>
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