问：请问如何限制应用程序只运行一次呢？
答：利用Windows的API函数FindWindow()、BringWindowToTop()、ShowWindow()可实现上述功能。

①定义API：
    Funtion ulong FindWindowA( ulong winhandle, string wintitle ) Library "user32"
    Funtion uLong BringWindowToTop( ulong hwnd ) Library "user32"
    Funtion uLong ShowWindow( ulong winhandle, int wincommand ) Library "user32"

②创建主窗口"w_test"，将title设置为"Test Window"

③在application的Open事件中加入如下代码:
    ulong ulng_winhandle
    ulng_winhandle = FindWindowA( 0,"Test Window" )
    If ulng_winhandle > 0 Then
        BringWindowToTop( ulng_winhandle )
        ShowWindow( ulng_winhandle, 5 )
        Return
    End If
    Open( w_test )

 

来自：https://www.cnblogs.com/lenya/archive/2010/11/12/3706967.html