第一个pdf页面的图像ios sdk [英] Image of the first pdf page ios sdk
问题描述
你知道如何在UfmageView中保存pdf文件的第一页吗?
我必须为pdf创建预览。
您有什么想法吗?
Do you know how to save into a UIImageView the first page of a pdf file? I have to create the preview for the pdf. Do you have any idea?
感谢您的帮助
Nicco
Thanks for help Nicco
推荐答案
以下方法将从PDF文件构建缩略图。它是RetinaDisplay识别的,因此缩略图在这些设备上应该特别清晰。
The following method will build a thumbnail from a PDF file. It is RetinaDisplay-aware, so the thumbnails should be especially crisp on such devices.
- (UIImage *)buildThumbnailImage
{
BOOL hasRetinaDisplay = FALSE; // by default
CGFloat pixelsPerPoint = 1.0; // by default (pixelsPerPoint is just the "scale" property of the screen)
if ([UIScreen instancesRespondToSelector:@selector(scale)]) // the "scale" property is only present in iOS 4.0 and later
{
// we are running iOS 4.0 or later, so we may be on a Retina display; we need to check further...
if ((pixelsPerPoint = [[UIScreen mainScreen] scale]) == 1.0)
hasRetinaDisplay = FALSE;
else
hasRetinaDisplay = TRUE;
}
else
{
// we are NOT running iOS 4.0 or later, so we can be sure that we are NOT on a Retina display
pixelsPerPoint = 1.0;
hasRetinaDisplay = FALSE;
}
size_t imageWidth = 320; // width of thumbnail in points
size_t imageHeight = 460; // height of thumbnail in points
if (hasRetinaDisplay)
{
imageWidth *= pixelsPerPoint;
imageHeight *= pixelsPerPoint;
}
size_t bytesPerPixel = 4; // RGBA
size_t bitsPerComponent = 8;
size_t bytesPerRow = bytesPerPixel * imageWidth;
void *bitmapData = malloc(imageWidth * imageHeight * bytesPerPixel);
// in the event that we were unable to mallocate the heap memory for the bitmap,
// we just abort and preemptively return nil:
if (bitmapData == NULL)
return nil;
// remember to zero the buffer before handing it off to the bitmap context:
bzero(bitmapData, imageWidth * imageHeight * bytesPerPixel);
CGContextRef theContext = CGBitmapContextCreate(bitmapData, imageWidth, imageHeight, bitsPerComponent, bytesPerRow,
CGColorSpaceCreateDeviceRGB(), kCGImageAlphaPremultipliedLast);
CGPDFDocumentRef pdfDocument = MyGetPDFDocumentRef(); // NOTE: you will need to modify this line to supply the CGPDFDocumentRef for your file here...
CGPDFPageRef pdfPage = CGPDFDocumentGetPage(pdfDocument, 1); // get the first page for your thumbnail
CGAffineTransform shrinkingTransform =
CGPDFPageGetDrawingTransform(pdfPage, kCGPDFMediaBox, CGRectMake(0, 0, imageWidth, imageHeight), 0, YES);
CGContextConcatCTM(theContext, shrinkingTransform);
CGContextDrawPDFPage(theContext, pdfPage); // draw the pdfPage into the bitmap context
CGPDFDocumentRelease(pdfDocument);
//
// create the CGImageRef (and thence the UIImage) from the context (with its bitmap of the pdf page):
//
CGImageRef theCGImageRef = CGBitmapContextCreateImage(theContext);
free(CGBitmapContextGetData(theContext)); // this frees the bitmapData we malloc'ed earlier
CGContextRelease(theContext);
UIImage *theUIImage;
// CAUTION: the method imageWithCGImage:scale:orientation: only exists on iOS 4.0 or later!!!
if ([UIImage respondsToSelector:@selector(imageWithCGImage:scale:orientation:)])
{
theUIImage = [UIImage imageWithCGImage:theCGImageRef scale:pixelsPerPoint orientation:UIImageOrientationUp];
}
else
{
theUIImage = [UIImage imageWithCGImage:theCGImageRef];
}
CFRelease(theCGImageRef);
return theUIImage;
}
您需要提供与您的PDF文件相对应的CGPDFDocumentRef,类似于以下。 (这个假定文件test.pdf存在于你的应用程序的主包中。)
You will need to supply a CGPDFDocumentRef corresponding to your PDF file, something like the following. (This one assumes that the file test.pdf exists in your app's main bundle.)
CGPDFDocumentRef MyGetPDFDocumentRef()
{
NSString *inputPDFFile = [[[NSBundle mainBundle] bundlePath] stringByAppendingPathComponent:@"test.pdf"];
const char *inputPDFFileAsCString = [inputPDFFile cStringUsingEncoding:NSASCIIStringEncoding];
//NSLog(@"expecting pdf file to exist at this pathname: \"%s\"", inputPDFFileAsCString);
CFStringRef path = CFStringCreateWithCString(NULL, inputPDFFileAsCString, kCFStringEncodingUTF8);
CFURLRef url = CFURLCreateWithFileSystemPath(NULL, path, kCFURLPOSIXPathStyle, 0);
CFRelease (path);
CGPDFDocumentRef document = CGPDFDocumentCreateWithURL(url);
CFRelease(url);
if (CGPDFDocumentGetNumberOfPages(document) == 0)
{
printf("Warning: No pages in pdf file \"%s\" or pdf file does not exist at this path\n", inputPDFFileAsCString);
return NULL;
}
return document;
}
最后,您可以在UIImageView中显示缩略图,如下所示:
Finally, you can display the thumbnail image in an UIImageView, like so:
UIImageView *thumbnailImageView = [[UIImageView alloc] initWithImage:[self buildThumbnailImage]];
[self.view addSubview:thumbnailImageView];
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