JNA - How to convert LPARAM pointer to a Class object?

Question

I am novice jn JNA and am getting a bit confused with mixture of java and C++. In the WNDPROC callback method, the LPARAM is sent to the callback has to be used to retrive the DEV_BROADCAST_DEVICEINTERFACE class object. This is my code:

    public static User32.WNDPROC WndProc = new User32.WNDPROC() {    
        @Override     
        public LRESULT callback(HWND hWnd, int uMSG, WPARAM uParam, LPARAM lParam)    
        {
             User32.DEV_BROADCAST_DEVICEINTERFACE b = (User32.DEV_BROADCAST_DEVICEINTERFACE)      lParam;                                      

             if(b != null){ 
                 System.out.println("Device Name: " + b.dbcc_name.toString ());           System.out.println("New Volume GUID:" +     b.dbcc_classguid.toString());
             }
        }

The compiler begins to complain when I try to convert the lParam to class object, for obvious reasons. How do I achieve this?

technomage · Accepted Answer · 2012-08-27 15:38:50Z

1

You don't have to use LPARAM; if you're being passed a structure (or other specific type) by the native code, you can define the appropriate method signature and JNA will do the right thing, converting the native value into something useful in Java.

public LRESULT callback(HWND hWnd, int uMSG, WPARAM uParam, User32.DEV_BROADCAST_DEVICEINTERFACE lParam);

answered Aug 27, 2012 at 15:38

technomage

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