代码在这里可能会有所帮助。一旦您了解了这些宏的作用以及如何将 java 和 cocoa 关注点相互分离，这并不像您想象的那么困难。
您需要记住的是，JNF_COCOA_ENTER 和 JNF_COCOA_EXIT 为您做了两件主要的事情：
他们建立了一个本地范围（因此内部定义的变量在外部不可用 - 这是为了帮助您不要用您不应该接触的变量做“愚蠢”的事情）并设置一个自动释放池，所以当范围消失时，在该范围内“自动释放”的可可对象将消失。 （这是局部作用域有用/有帮助的部分原因）他们还将进行一些异常解析，以便您可以在 Java 中捕获 Cocoa 异常。
也就是说，以下代码是合法的，您只需要非常小心地管理内存访问和数据的所有权。尽可能避免混合 Java 所有权和 Objective-C 所有权，否则让您的对象管理所有权，并在 Java 对象被 GC 时清理。
jbyteArray bytes;
JNF_COCOA_ENTER(env);
// Assign and full the bytes array here, doing any requisite transformations.
// Remember to COPY any data out of COCOA objects, as references will be dead soon!
JNF_COCOA_EXIT(env);
return bytes;
从 C 中使用 Java 对象很复杂，但并非不可行。尽管如此，方法调用的次数还是很重要的，并且向后跳转和第四次跳转非常耗时，因此如果您会经常调用此方法，或者时间紧迫，请尽可能坚持使用基本类型。
如果您需要从委托将数据从 Cocoa 推送到 Java，事情会稍微复杂一些，但并非不可行。这是我管理的一个名为 QTCubed 的项目的一部分，它就是这样做的。 didOutputVideoFrame 是委托方法，该对象必须使用目标 Java 对象引用和来自 JNI 调用方法的 Java 环境进行初始化。初始化后，它会被设置为委托对象，并从相机接收更新。
@implementation QTKitCaptureDecompressedVideoOutput
- (QTKitCaptureDecompressedVideoOutput *)initWithEnv:(JNIEnv *) env javaObject:(jobject) javaObjectRef {
[super init];
// Save a reference to the VM
(*env)->GetJavaVM(env,&g_vm);
// Create a global reference to this object so we can access it later
objectRef = (*env)->NewGlobalRef(env,javaObjectRef);
return self;
}
- (void)captureOutput:(QTCaptureOutput *)captureOutput didOutputVideoFrame:(CVImageBufferRef)videoFrame withSampleBuffer:(QTSampleBuffer *)sampleBuffer fromConnection:(QTCaptureConnection *)connection {
// Move into Java to deliver the data
JNIEnv *env;
(*g_vm)->AttachCurrentThread (g_vm, (void **) &env, NULL);
void * rawData = [sampleBuffer bytesForAllSamples];
int length = [sampleBuffer lengthForAllSamples];
QTFormatDescription * formatDescription = [sampleBuffer formatDescription];
QTTime duration = [sampleBuffer duration];
float frameDuration = duration.timeValue/duration.timeScale;
float fps = 1/frameDuration;
jint format = [formatDescription formatType];
NSValue * pixelSize = [formatDescription attributeForKey:QTFormatDescriptionVideoEncodedPixelsSizeAttribute];
NSSize size = [pixelSize sizeValue];
jint width = size.width;
jint height = size.height;
//NSLog(@"Outputting frame sized %d x %d of length %d with format: %#x",width,height,length,format);
switch (format) {
// 8 bit codecs
case kCVPixelFormatType_1Monochrome:
case kCVPixelFormatType_2Indexed:
case kCVPixelFormatType_4Indexed:
case kCVPixelFormatType_8Indexed:
case kCVPixelFormatType_1IndexedGray_WhiteIsZero:
case kCVPixelFormatType_2IndexedGray_WhiteIsZero:
case kCVPixelFormatType_4IndexedGray_WhiteIsZero:
case kCVPixelFormatType_8IndexedGray_WhiteIsZero:
case kCVPixelFormatType_422YpCbCr8:
case kCVPixelFormatType_4444YpCbCrA8:
case kCVPixelFormatType_4444YpCbCrA8R:
case kCVPixelFormatType_444YpCbCr8:
case kCVPixelFormatType_420YpCbCr8Planar:
case kCVPixelFormatType_422YpCbCr_4A_8BiPlanar:
case kCVPixelFormatType_24RGB:
case kCVPixelFormatType_24BGR:
default:
{
// Re-use the existing array if possible
if (byteFrameData == nil || (*env)->GetArrayLength(env,byteFrameData) < length) {
// Clean up the previously allocated global reference
if (byteFrameData != nil) {
(*env)->DeleteGlobalRef(env,byteFrameData);
byteFrameData = nil;
}
// Create an appropriately sized byte array to hold the data
byteFrameData = (*env)->NewGlobalRef(env,(*env)->NewByteArray(env,length));
}
if (byteFrameData) {
// Copy the raw data into the byteArray
(*env)->SetByteArrayRegion(env,byteFrameData,0,length,rawData);
// Get the class reference for our object
jclass classRef = (*env)->GetObjectClass(env,objectRef);
// Get the pushFrame methodId
jmethodID methodId = (*env)->GetMethodID(env,classRef,"pushFrame","([BIIIF)V");
// Call pushFrame with the byte array
(*env)->CallVoidMethod(env,objectRef,methodId,byteFrameData,format,width,height,fps);
}
break;
}
// 16 bit (short) storage of values
case kCVPixelFormatType_16BE555:
case kCVPixelFormatType_16LE555:
case kCVPixelFormatType_16LE5551:
case kCVPixelFormatType_16BE565:
case kCVPixelFormatType_16LE565:
case kCVPixelFormatType_16Gray:
case kCVPixelFormatType_422YpCbCr16:
case kCVPixelFormatType_422YpCbCr10:
case kCVPixelFormatType_444YpCbCr10:
{
// Re-use the existing array if possible
if (shortFrameData == nil || (*env)->GetArrayLength(env,shortFrameData) < length/2) {
// Clean up the previously allocated global reference
if (shortFrameData != nil) {
(*env)->DeleteGlobalRef(env,shortFrameData);
shortFrameData = nil;
}
// Create an appropriately sized byte array to hold the data
shortFrameData = (*env)->NewGlobalRef(env,(*env)->NewShortArray(env,length/2));
}
if (shortFrameData) {
// Copy the raw data into the byteArray
(*env)->SetShortArrayRegion(env,shortFrameData,0,length/2,rawData);
// Get the class reference for our object
jclass classRef = (*env)->GetObjectClass(env,objectRef);
// Get the pushFrame methodId
jmethodID methodId = (*env)->GetMethodID(env,classRef,"pushFrame","([SIIIF)V");
// Call pushFrame with the short array
(*env)->CallVoidMethod(env,objectRef,methodId,shortFrameData,format,width,height,fps);
}
break;
}
// 32 bit (int) storage of values
case kCVPixelFormatType_32ABGR:
case kCVPixelFormatType_32AlphaGray:
case kCVPixelFormatType_32ARGB:
case kCVPixelFormatType_32BGRA:
case kCVPixelFormatType_32RGBA:
{
// Re-use the existing array if possible
if (intFrameData == nil || (*env)->GetArrayLength(env,intFrameData) < length/4) {
// Clean up the previously allocated global reference
if (intFrameData != nil) {
(*env)->DeleteGlobalRef(env,intFrameData);
intFrameData = nil;
}
// Create an appropriately sized byte array to hold the data
intFrameData = (*env)->NewGlobalRef(env,(*env)->NewIntArray(env,length/4));
}
if (intFrameData) {
// Copy the raw data into the byteArray
(*env)->SetByteArrayRegion(env,intFrameData,0,length/4,rawData);
// Get the class reference for our object
jclass classRef = (*env)->GetObjectClass(env,objectRef);
// Get the pushFrame methodId
jmethodID methodId = (*env)->GetMethodID(env,classRef,"pushFrame","([IIIIF)V");
// Call pushFrame with the int array
(*env)->CallVoidMethod(env,objectRef,methodId,intFrameData,format,width,height,fps);
}
break;
}
}
// Detatch from Java
(*g_vm)->DetachCurrentThread (g_vm);
}
/* Clean up java references so they can be properly GCed in java */
- (void) dealloc {
// Attach to java so we can release references
JNIEnv *env;
(*g_vm)->AttachCurrentThread (g_vm, (void **) &env, NULL);
// release the references we hold
if (objectRef != nil) {
(*env)->DeleteGlobalRef(env,objectRef);
objectRef = nil;
}
if (byteFrameData != nil) {
(*env)->DeleteGlobalRef(env,byteFrameData);
byteFrameData = nil;
}
if (shortFrameData != nil) {
(*env)->DeleteGlobalRef(env,shortFrameData);
shortFrameData = nil;
}
if (intFrameData != nil) {
(*env)->DeleteGlobalRef(env,intFrameData);
intFrameData = nil;
}
// Detatch from Java
(*g_vm)->DetachCurrentThread (g_vm);
g_vm = nil;
[super dealloc];
}
@end
这是传入的 java 对象引用在 java 端的方法签名：
protected void pushFrame(byte[] frameData, int formatInt, int width, int height, float frameRate);
protected void pushFrame(short[] frameData, int formatInt, int width, int height, float frameRate);
protected void pushFrame(int[] frameData, int formatInt, int width, int height, float frameRate);
一旦你有一个正在运行的应用程序，使用工具来确保你正确地处理引用！