Iphone 尝试在后台保存图像

我试图在主线程之外的其他线程中调用

UIImagePNGRepresentation

，但只得到EXC\u BAD\u访问异常

这是代码

UIImage *imageToSave = [UIImage imageWithCGImage:imageRef];

dispatch_queue_t taskQ = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);

dispatch_async(taskQ,
               ^{
                   NSData *binaryImage = UIImagePNGRepresentation(imageToSave);

                   if (![binaryImage writeToFile:destinationFilePath atomically:YES]) {
                       SCASSERT(assCodeCannotCreateFile, @"Write of image file failed!");
                   };
               });

尝试访问imageToSave变量时发生异常

编辑： 我想把OpenGLSCeene保存到PNG文件中，里面有整个函数的代码

- (void)saveImage:(NSString *)destinationFilePath {

NSUInteger width  = (uint)self.frame.size.width;
NSUInteger height = (uint)self.frame.size.height;

NSUInteger myDataLength = width * height * 4;

// allocate array and read pixels into it.
GLubyte *buffer = (GLubyte *)malloc(myDataLength);
glReadPixels(0, 0, width, height, GL_RGBA, GL_UNSIGNED_BYTE, buffer);

// gl renders "upside down" so swap top to bottom into new array.
// there's gotta be a better way, but this works.
GLubyte *buffer2 = (GLubyte *)malloc(myDataLength);

for (int y = 0; y <height; y++) {
    for (int x = 0; x <width * 4; x++) {
        buffer2[((int)height - 1 - y) * (int)width * 4 + x] = buffer[y * 4 * (int)width + x];
    }
}

JFFree(buffer);

// make data provider with data.
CGDataProviderRef provider = CGDataProviderCreateWithData(NULL, buffer2, myDataLength, NULL);

// prep the ingredients
int bitsPerComponent = 8;
int bitsPerPixel = 32;
int bytesPerRow = 4 * width;
CGColorSpaceRef colorSpaceRef = CGColorSpaceCreateDeviceRGB();
CGBitmapInfo bitmapInfo = kCGImageAlphaPremultipliedLast;
CGColorRenderingIntent renderingIntent = kCGRenderingIntentDefault;

// make the cgimage
CGImageRef imageRef = CGImageCreate(width, 
                                    height, 
                                    bitsPerComponent, 
                                    bitsPerPixel,
                                    bytesPerRow,
                                    colorSpaceRef,
                                    bitmapInfo,
                                    provider,
                                    NULL,
                                    NO,
                                    renderingIntent);

UIImage *imageToSave = [UIImage imageWithCGImage:imageRef];

dispatch_queue_t taskQ = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);

dispatch_async(taskQ,
               ^{
                   NSData *binaryImage = UIImagePNGRepresentation(imageToSave);

                   if (![binaryImage writeToFile:destinationFilePath atomically:YES]) {
                       SCASSERT(assCodeCannotCreateFile, @"Write of image file failed!");
                   };
               });

// release resources
CGColorSpaceRelease(colorSpaceRef);
CGDataProviderRelease(provider);
CGImageRelease(imageRef);
JFFree(buffer2);
}

-（void）saveImage:（NSString*）destinationFilePath{
NSUInteger width=（uint）self.frame.size.width；
NSU整数高度=（uint）self.frame.size.height；
NSUInteger myDataLength=宽度*高度*4；
//分配数组并将像素读入其中。
GLubyte*buffer=（GLubyte*）malloc（myDataLength）；
glReadPixels（0，0，宽度，高度，GL_RGBA，GL_无符号字节，缓冲区）；
//gl呈现“倒置”，以便从上到下交换到新阵列中。
//肯定有更好的办法，但这是可行的。
GLubyte*buffer2=（GLubyte*）malloc（myDataLength）；
对于（int y=0；y省略CGImageRelease调用，因为UIImage不保留CGImageRef

请参见
检查您的imageToSave是否为零？？？您是否使用ARC？我使用的是ARC，imageToSave不是零。它是UIImage对象。我检查了它在主线程上时是否工作？是的，就是这样。当我在
调度\u async
中移动“//release resources”之后的所有释放代码时，它工作了。感谢您的帮助