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// __________ Imports __________

import java.awt.*;

// __________ Implementation __________

/**
 * Class to pass the system window handle to the OpenOffice.org toolkit.
 * It use special JNI methods to get the system handle of used java window.
 *
 * Attention!
 * Use JNI functions on already visible canvas objects only!
 * Otherwise they can make some trouble.
 *
 */

public class NativeView extends java.awt.Canvas
{


    /**
     * ctor
     * Does nothing really.
     * We can use our JNI mechanism for an already visible
     * canvas only. So we override the method for showing ("setVisible()")
     * and make our initialization there. But we try to show an empty clean
     * window till there.
     */
    public NativeView()
    {
        maHandle = null;
        maSystem = 0;
        this.setBackground(Color.white);
    }



    /**
     * Override this method to make necessary initializations here.
     * (e.g. get the window handle and necessary system information)
     *
     * Why here?
     * Because the handle seems to be available for already visible windows
     * only. So it's the best place to get it. Special helper method
     * can be called more than ones - but call native code one times only
     * and safe the handle and the system type on our members maHandle/maSystem!
     */
    @Override
    public void setVisible(boolean bState)
    {
        getHWND();
    }



    /**
     * to guarantee right resize handling inside a swing container
     * (e.g. JSplitPane) we must provide some information about our
     * preferred/minimum and maximum size.
     */
    @Override
    public Dimension getPreferredSize()
    {
        return new Dimension(500,300);
    }

    @Override
    public Dimension getMaximumSize()
    {
        return new Dimension(1024,768);
    }

    @Override
    public Dimension getMinimumSize()
    {
        return new Dimension(100,100);
    }



    /**
     * Override paint routine to show provide against
     * repaint errors if no office view is really plugged
     * into this canvas.
     * If handle is present - we shouldn't paint anything further.
     * May the remote window is already plugged. In such case we
     * shouldn't paint it over.
     */
    @Override
    public void paint(Graphics aGraphic)
    {
        if(maHandle==null)
        {
            Dimension aSize = getSize();
            aGraphic.clearRect(0,0,aSize.width,aSize.height);
        }
    }



    /**
     * JNI interface of this class
     * These two methods are implemented by using JNI mechanismen.
     * The will be used to get the platform dependent window handle
     * of a java awt canvas. This handle can be used to create an office
     * window as direct child of it. So it's possible to plug Office
     * windows in a java UI container.
     *
     * Note:
     * Native code for Windows registers a special function pointer to handle
     * window messages... But if it doesn't check for an already-registered
     * instance of this handler it will do it twice and produce a stack overflow
     * because such method calls itself in a never-ending loop...
     * So we try to use the JNI code one time only and save already-obtained
     * information inside this class.
     */
    public  native int  getNativeWindowSystemType();
    private native long getNativeWindow(); // private! => use getHWND() with cache mechanism!

    public Integer getHWND()
    {
        if(maHandle==null)
        {
            maHandle = Integer.valueOf((int)getNativeWindow());
            maSystem = getNativeWindowSystemType();
        }
        return maHandle;
    }



    /**
     * for using of the JNI methods it's necessary to load
     * system library which exports it.
     */
    static
    {
        System.loadLibrary("nativeview");
    }



    /**
     * @member  maHandle    system window handle
     * @member  maSystem    info about currently used platform
     */
    public Integer maHandle ;
    public int     maSystem ;
}

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