将UIImage/CGImage渲染为CGPDFContext的结果为...一片空白！

Question

我正在尝试获取图像对象中的图像，并将其呈现到Core Graphics PDF上下文中--恰好在iPhone上，但这个问题肯定也适用于桌面Quartz。这个UIImage是一张简单的白底彩色图像，分辨率约为600x800。如果我(比方说)将其转换为PNG文件，则该文件看起来与预期的完全一样--因此数据是正确的。

下面是我用来生成PDF的方法：

NSMutableData * outputData = [[NSMutableData alloc] init];
CGDataConsumerRef dataConsumer = CGDataConsumerCreateWithCFData((CFMutableDataRef)outputData);

CFMutableDictionaryRef attrDictionary = NULL;    
attrDictionary = CFDictionaryCreateMutable(NULL, 0,
                                         &kCFTypeDictionaryKeyCallBacks,
                                         &kCFTypeDictionaryValueCallBacks);
CFDictionarySetValue(attrDictionary, kCGPDFContextTitle, @"My Awesome Document");
CGContextRef pdfContext = CGPDFContextCreate(dataConsumer, NULL, attrDictionary); 
CFRelease(dataConsumer);
CFRelease(attrDictionary);
CGImageRef pageImage = [myUIImage CGImage];
CGPDFContextBeginPage(pdfContext, NULL);
CGContextDrawImage(pdfContext, CGRectMake(0, 0, [myUIImage size].width, [myUIImage size].height), pageImage);
CGPDFContextEndPage(pdfContext);
CGPDFContextClose(pdfContext);
CGContextRelease(pdfContext);

生成的outputData文件看起来像是一个有效的PDF文件(正确打开，文档标题显示在元数据中)，但它只由一个空白页面组成。

我做错了什么？

谢谢。

更新:哈！这都是我的错。我只生成PNG文件的测试代码通过一个不同的路径来获取数据。PDF路径确实接收到了一个空图像。

Answer 1

我测试了你的代码，它似乎可以工作。

您确定您的UIImage是有效的，并且在将其绘制到上下文中时不为空吗？

我的测试方法从主包加载一个.png，并将最终的pdf写入应用程序文档文件夹中的一个文件：

- (IBAction)outputPDF:(id)sender
{
    NSMutableData* outputData = [[NSMutableData alloc] init];
    CGDataConsumerRef dataConsumer = CGDataConsumerCreateWithCFData((CFMutableDataRef)outputData);
    CFMutableDictionaryRef attrDictionary = NULL;    
    attrDictionary = CFDictionaryCreateMutable(NULL, 0, &kCFTypeDictionaryKeyCallBacks, &kCFTypeDictionaryValueCallBacks);
    CFDictionarySetValue(attrDictionary, kCGPDFContextTitle, @"My Awesome Document");
    CGContextRef pdfContext = CGPDFContextCreate(dataConsumer, NULL, attrDictionary); 
    CFRelease(dataConsumer);
    CFRelease(attrDictionary);
    UIImage* myUIImage = [UIImage imageNamed:@"tmp.png"];
    CGImageRef pageImage = [myUIImage CGImage];
    CGPDFContextBeginPage(pdfContext, NULL);
    CGContextDrawImage(pdfContext, CGRectMake(0, 0, [myUIImage size].width, [myUIImage size].height), pageImage);
    CGPDFContextEndPage(pdfContext);
    CGPDFContextClose(pdfContext);
    CGContextRelease(pdfContext);   
    NSArray* paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
    NSString* documentsDirectory = [paths objectAtIndex:0];
    NSString* appFile = [documentsDirectory stringByAppendingPathComponent:@"tmp.pdf"];
    [outputData writeToFile:appFile atomically:YES];
}

Answer 2

这个问题似乎已经在iphone dev sdk论坛上得到了解决：PDF creation tutorial

所有的功劳都归功于danielb21:这是他们的CreatePDFFile方法的重印本：

// Our method to create a PDF file natively on the iPhone
// This method takes two parameters, a CGRect for size and
// a const char, which will be the name of our pdf file
void CreatePDFFile (CGRect pageRect, const char *filename) {

    // This code block sets up our PDF Context so that we can draw to it
    CGContextRef pdfContext;
    CFStringRef path;
    CFURLRef url;
    CFMutableDictionaryRef myDictionary = NULL;
    // Create a CFString from the filename we provide to this method when we call it
    path = CFStringCreateWithCString (NULL, filename,
                                      kCFStringEncodingUTF8);
    // Create a CFURL using the CFString we just defined
    url = CFURLCreateWithFileSystemPath (NULL, path,
                                         kCFURLPOSIXPathStyle, 0);
    CFRelease (path);
    // This dictionary contains extra options mostly for 'signing' the PDF
    myDictionary = CFDictionaryCreateMutable(NULL, 0,
                                             &kCFTypeDictionaryKeyCallBacks,
                                             &kCFTypeDictionaryValueCallBacks);
    CFDictionarySetValue(myDictionary, kCGPDFContextTitle, CFSTR("My PDF File"));
    CFDictionarySetValue(myDictionary, kCGPDFContextCreator, CFSTR("My Name"));
    // Create our PDF Context with the CFURL, the CGRect we provide, and the above defined dictionary
    pdfContext = CGPDFContextCreateWithURL (url, &pageRect, myDictionary);
    // Cleanup our mess
    CFRelease(myDictionary);
    CFRelease(url);
    // Done creating our PDF Context, now it's time to draw to it

    // Starts our first page
    CGContextBeginPage (pdfContext, &pageRect);

    // Draws a black rectangle around the page inset by 50 on all sides
    CGContextStrokeRect(pdfContext, CGRectMake(50, 50, pageRect.size.width - 100, pageRect.size.height - 100));

    // This code block will create an image that we then draw to the page
    const char *picture = "Picture";
    CGImageRef image;
    CGDataProviderRef provider;
    CFStringRef picturePath;
    CFURLRef pictureURL;

    picturePath = CFStringCreateWithCString (NULL, picture,
                                      kCFStringEncodingUTF8);
    pictureURL = CFBundleCopyResourceURL(CFBundleGetMainBundle(), picturePath, CFSTR("png"), NULL);
    CFRelease(picturePath);
    provider = CGDataProviderCreateWithURL (pictureURL);
    CFRelease (pictureURL);
    image = CGImageCreateWithPNGDataProvider (provider, NULL, true, kCGRenderingIntentDefault);
    CGDataProviderRelease (provider);
    CGContextDrawImage (pdfContext, CGRectMake(200, 200, 207, 385),image);
    CGImageRelease (image);
    // End image code

    // Adding some text on top of the image we just added
    CGContextSelectFont (pdfContext, "Helvetica", 16, kCGEncodingMacRoman);
    CGContextSetTextDrawingMode (pdfContext, kCGTextFill);
    CGContextSetRGBFillColor (pdfContext, 0, 0, 0, 1);
    const char *text = "Hello World!";
    CGContextShowTextAtPoint (pdfContext, 260, 390, text, strlen(text));
    // End text

    // We are done drawing to this page, let's end it
    // We could add as many pages as we wanted using CGContextBeginPage/CGContextEndPage
    CGContextEndPage (pdfContext);

    // We are done with our context now, so we release it
    CGContextRelease (pdfContext);
}