我正在尝试创建一个简单的 Java 应用程序，该应用程序显示一个包含 JButton 的框架。我正在使用 JNI 为窗口添加透明度。窗口是透明的，但按钮不是。此外，当我移动窗口时，按钮不会随窗口移动。JLabel 也会发生同样的事情。如果我使用 Button 而不是 JButton 它工作得很好。
本机代码：
#include <windows.h>
#include <jawt_md.h>
#include <jawt.h>
#include <jni.h>
// Don't mangle names for the JVM
extern "C" {
BOOL APIENTRY DllMain( HMODULE hModule,
DWORD ul_reason_for_call,
LPVOID lpReserved
)
{
switch (ul_reason_for_call)
{
case DLL_PROCESS_ATTACH:
case DLL_THREAD_ATTACH:
case DLL_THREAD_DETACH:
case DLL_PROCESS_DETACH:
break;
}
return TRUE;
}
/**
* Gets the window handle for the Java window.
* Procedure for obtaining the handle:
* 1. Get the structure (JAWT) that contains the native methods.
* 2. Get the drawing surface (JAWT_DrawingSurface).
* 3. Using the drawing surface, get the drawing surface info (JAWT_DrawingSurfaceInfo).
* 4. Get the drawing info that's specific to Win32 (JAWT_Win32DrawingSurfaceInfo).
* 5. Using the drawing surface info, get the hwnd.
*/
/*
* Class: test_Transparency
* Method: getWindowHandle
* Signature: (Ljava/awt/Component;)J
*/
JNIEXPORT jlong JNICALL Java_test_Transparency_getWindowHandle
(JNIEnv * env, jclass cls, jobject component)
{
JAWT awt;
JAWT_DrawingSurface* ds;
JAWT_DrawingSurfaceInfo* dsi;
JAWT_Win32DrawingSurfaceInfo* dsi_win;
jint dsLock;
jboolean result = JNI_FALSE;
// Get the AWT
awt.version = JAWT_VERSION_1_4;
result = JAWT_GetAWT(env, &awt);
if ( result == JNI_FALSE )
{
printf( "%s:%i - JAWT_GetAWT() failed.\n", __FILE__, __LINE__ );
return 0;
}
// Get the drawing surface
ds = awt.GetDrawingSurface(env, component);
if ( ds == NULL )
{
printf( "%s:%i - GetDrawingSurface() failed.\n", __FILE__, __LINE__ );
return 0;
}
dsLock = ds->Lock(ds);
// Get the drawing surface info
dsi = ds->GetDrawingSurfaceInfo(ds);
// Get the platform-specific drawing info
dsi_win = (JAWT_Win32DrawingSurfaceInfo*)dsi->platformInfo;
HWND handle = dsi_win->hwnd;
ds->FreeDrawingSurfaceInfo(dsi);
ds->Unlock(ds);
awt.FreeDrawingSurface(ds);
return (jlong)handle;
}
void printLastError()
{
LPTSTR pszMessage;
DWORD dwLastError = GetLastError();
FormatMessage(
FORMAT_MESSAGE_ALLOCATE_BUFFER |
FORMAT_MESSAGE_FROM_SYSTEM |
FORMAT_MESSAGE_IGNORE_INSERTS,
NULL,
dwLastError,
MAKELANGID(LANG_NEUTRAL, SUBLANG_DEFAULT),
(LPTSTR)&pszMessage,
0, NULL );
// Display the error message
wprintf(L"failed with error %d: %s\n", dwLastError, pszMessage);
LocalFree(pszMessage);
}
/*
* Class: test_Transparency
* Method: setTransparency
* Signature: (JF)V
*/
JNIEXPORT void JNICALL Java_test_Transparency_setTransparency
(JNIEnv * env, jclass cls, jlong windowHandle, jfloat alpha)
{
HWND hwnd = (HWND)windowHandle;
// Get the current window style
LONG currentStyle = GetWindowLong(hwnd, GWL_EXSTYLE);
if ( currentStyle == 0 )
{
printf( "Error calling GetWindowLong() ");
printLastError();
}
if ( alpha == 0 )
{
// No transparency.
// Remove WS_EX_LAYERED from this window style
SetWindowLong(hwnd, GWL_EXSTYLE, currentStyle & ~WS_EX_LAYERED);
}
else
{
// Calculate the transparency value. Should be in the range 0-255
unsigned char transparency = (unsigned char)(255 * alpha);
// Set window style to WS_EX_LAYERED. This is required for windows to be transparent.
SetWindowLong(hwnd, GWL_EXSTYLE, currentStyle | WS_EX_LAYERED );
// set the transparency level
SetLayeredWindowAttributes(hwnd, 0, transparency, LWA_ALPHA);
}
}
} // extern "C"
MyFrame.java
package test;
import javax.swing.*;
import javax.swing.SwingUtilities;
import java.awt.event.*;
public class MyFrame implements ActionListener
{
private JFrame frame;
private Transparency trans; // = new Transparency();
private float t = 1.0f;
public MyFrame()
{
frame = new JFrame("My transparent window");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setBounds( 10, 10, 200, 200 );
JButton button = new JButton("My button");
button.setBounds( 20, 20, 50, 10 );
button.addActionListener( this );
JPanel panel = new JPanel();
panel.add( button );
frame.setContentPane( panel );
//Display the window.
frame.setVisible(true);
trans = new Transparency();
}
/**
* @param args
*/
public static void main( String[] args )
{
MyFrame f = new MyFrame();
}
public void actionPerformed(ActionEvent e)
{
t -= 0.05f;
trans.setWindowOpacity( frame, t );
}
}
透明度.java
package test;
import java.awt.Window;
import java.awt.Component;
public class Transparency
{
static boolean libLoaded = false;
/**
* Sets the transparency for a window.
* @param hwnd Handle for the window.
* @param opacity Transparency level, from 0.0 to 1.0.
* 1.0 is completely transparent. 0.0 is completely opaque.
*/
private static native void setTransparency( long hwnd, float opacity );
/**
* Get the window handle for the component.
* @param component
* @return HWND value obtained from the OS.
*/
private static native long getWindowHandle( Component component );
static
{
try
{
System.loadLibrary("transJNI");
libLoaded = true;
}
catch ( Exception e )
{
e.printStackTrace();
libLoaded = false;
}
}
/**
* @param window The window whose opacity will be adjusted.
* @param opacity The opacity level, from 0.0 (opaque) to 1.0 (completely transparent).
*/
public void setWindowOpacity(Window window, float opacity)
{
if ( !libLoaded )
{
return;
}
if ( !window.isVisible() )
{
return;
}
long hwnd = getWindowHandle( window );
setTransparency(hwnd, opacity);
}
}