您知道如何在UfmageView中保存pdf文件的第一页吗？ 我必须为pdf创建预览。 你有什么想法吗？
感谢您的帮助 NICCO
答案 0 :(得分：8)
以下方法将从PDF文件构建缩略图。它具有RetinaDisplay感知功能，因此缩略图在这些设备上应该特别清晰。
- (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PDF文件相对应的CGPDFDocumentRef，如下所示。 （这假设文件test.pdf存在于您应用程序的主包中。）
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：
UIImageView *thumbnailImageView = [[UIImageView alloc] initWithImage:[self buildThumbnailImage]];
[self.view addSubview:thumbnailImageView];
答案 1 :(得分：6)
作为我正在研究的项目的一部分，我修改了inwit的代码，以便在调用中使用变量。我想我会把它们发布在这里，以帮助那些正在寻找类似解决方案的人：
打电话给他们：
//Assume all your PDFs you want to create thumbnails for are in an array. This method saves the paths to all PDFs in your main bundle as NSStrings.
_pdfs = [[NSBundle mainBundle] pathsForResourcesOfType:@"pdf" inDirectory:nil];
//To be called in the cellForItemAtIndexPath method or a similar method where you want to create a thumbnail for the image:
NSString *loc = [_pdfs objectAtIndex:indexPath.row];
UIImage *cellImage = [self buildThumbnailImage:MyGetPDFDocumentRef(loc)];
方法和C函数：
- (UIImage *)buildThumbnailImage:(CGPDFDocumentRef)pdfDocument
{
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;
}
CGPDFDocumentRef MyGetPDFDocumentRef(NSString *inputPDFFile)
{
//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;
}
答案 2 :(得分：0)
有很多方法可以截取UIViews的截图：
看这里 http://www.icodeblog.com/2009/07/27/1188/
另见： How Do I Take a Screen Shot of a UIView?
这可能很麻烦，但您可以在UIWebview中打开PDF，使用上面链接到UIImageView的代码中的第一页的屏幕截图。然后关闭PDF。
答案 3 :(得分：0)
这是你要找的吗？ - http://ipdfdev.com/2011/03/28/convert-a-pdf-page-to-image-on-the-iphone-and-ipad/。输出是UIImage，因此您应该能够在UIImageView中显示它。